Materiały źródłowe

• #1 What causes Down syndrome? | NICHD – Eunice Kennedy Shriver National Institute of Child Health and Human Development

  http://www.nichd.nih.gov/health/topics/down/conditioninfo/causes

  Down syndrome is caused by a random error in cell division that results in the presence of an extra copy of chromosome 21. […] The type of error is called nondisjunction. […] Most of the time, the error occurs at random during the formation of an egg or sperm. To date, no behavioral activity of the parents or environmental factor is known to cause Down syndrome. […] In the majority of cases, the extra copy of chromosome 21 comes from the mother through the egg. […] In a small percentage (less than 5%) of cases, the extra copy of chromosome 21 comes from the father through the sperm. […] In the remaining cases, the error occurs after fertilization, as the embryo grows. […] Research shows that three types of chromosomal changes can lead to Down syndrome. […] Complete trisomy 21. In this case, an error during the formation of the egg or the sperm results in either one having an extra chromosome.

• #1 What causes Down syndrome? | NICHD – Eunice Kennedy Shriver National Institute of Child Health and Human Development

  http://www.nichd.nih.gov/health/topics/down/conditioninfo/causes

  Almost all Down syndrome cases result from complete trisomy 21. […] Mosaic trisomy 21. […] In a small percentage (less than 5%) of Down syndrome cases, most of the cells in the body have the extra chromosome, but some of them don’t. […] Translocation trisomy 21. In this type of chromosomal change, only part of an extra copy of chromosome 21 is in the cells. […] Sometimes, a parent who does not have Down syndrome may carry a translocation in chromosome 21 that can be passed on to children and cause Down syndrome.

• #2 Down Syndrome: Symptoms & Causes

  https://my.clevelandclinic.org/health/diseases/17818-down-syndrome

  Down syndrome is a genetic condition where a person is born with an extra copy of chromosome 21. This means that they have a total of 47 chromosomes instead of 46. This can affect how their brain and body develop. […] Down syndrome can affect anyone. Its a genetic condition, and it doesnt happen as a result of something that the parents did before or during pregnancy. The majority of Down syndrome cases happen randomly (sporadically). People dont usually inherit Down syndrome in an autosomal dominant or recessive pattern during conception when the egg and sperm meet. […] An extra chromosome causes Down syndrome. Each human cell typically contains 23 pairs of chromosomes, which totals 46. Down syndrome occurs because of changes in the way cells in chromosome 21 divide. Every person with Down syndrome has an extra chromosome 21 in some or all of their cells.

• #2 Down Syndrome: Symptoms & Causes

  https://my.clevelandclinic.org/health/diseases/17818-down-syndrome

  There are three types of Down syndrome with different causes, including: Trisomy 21, Translocation, Mosaicism. […] Trisomy 21 is the most common type of Down syndrome. The term trisomy means having an extra copy of a chromosome. Trisomy 21 occurs when a developing fetus has three copies of chromosome 21 in every cell instead of the typical two copies. This type makes up 95% of all cases of Down syndrome. […] Translocation is a type of Down syndrome where theres a partial or full amount of chromosome 21 attached to another chromosome. Unlike trisomy 21, translocation occurs when chromosome 21 isnt separate, but it relocates to another numbered chromosome. This type of Down syndrome accounts for less than 4% of all cases. […] Mosaic Down syndrome is the rarest type of Down syndrome and accounts for less than 1% of all cases. Mosaicism occurs when only some cells contain the usual 46 chromosomes and some cells contain 47. The extra chromosome in some cells is chromosome 21.

• #3 Down Syndrome – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK526016/

  Down syndrome (trisomy 21) is a genetic disorder caused by the presence of all or a portion of a third chromosome 21. […] It is the presence of all or part of the third copy of chromosome 21 that causes Down syndrome, the most common chromosomal abnormality occurring in humans. […] The majority of patients with Down syndrome have an extra copy of chromosome 21. […] Among them is gene dosage imbalance, in which there is an increased dosage or number of genes of Hsa21, which results in increased gene expansion. […] The other popular hypothesis is the amplified development instability hypothesis, according to which the genetic imbalance created by a number of trisomic genes results in a greater impact on the expression and regulation of many genes. […] The critical region hypothesis is also well-known in this list. Down syndrome critical regions (DSCR) are a few chromosomal regions that are associated with partial trisomy for Has21. […] After a thorough study of different analyses, it became clear that a single critical region gene cannot cause all the phenotypical features associated with trisomy 21, rather it is more evident that multiple critical regions or critical genes have a role to play in this phenomenon.

• #4 Down Syndrome: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/943216-overview

  Down syndrome is caused primarily by trisomy of chromosome 21; this is the most common trisomy among live births. […] Down syndrome is caused by the following three cytogenic variants: Three full copies of chromosome 21, Chromosomal translocation that results in three copies of the DSCR, Mosaicism. […] In 94% of patients with Down syndrome, full trisomy 21 is the cause; mosaicism (2.4%) and translocations (3.3%) account for the remaining cases. […] A free trisomy 21 results from nondisjunction during meiosis in one of the parents. This occurrence is correlated with advanced maternal and paternal age. […] Advanced maternal age remains the only well-documented risk factor for maternal meiotic nondisjunction. […] Translocation occurs when genetic material from chromosome 21 becomes attached to another chromosome, resulting in 46 chromosomes, with 1 chromosome having extra material from chromosome 21 attached. […] Mosaicism is considered a postzygotic event (ie, one that occurs after fertilization). […] Cytogenetic and molecular studies suggest that dup21(q22.1-22.2) is sufficient to cause Down syndrome.

• #5 Down syndrome: MedlinePlus GeneticsLock

  https://medlineplus.gov/genetics/condition/down-syndrome/

  Down syndrome occurs in about 1 in 700 newborns. About 5,300 babies with Down syndrome are born in the United States each year, and approximately 200,000 people in this country have the condition. Although women of any age can have a child with Down syndrome, the chance of having a child with this condition increases as a woman gets older. […] Most cases of Down syndrome result from trisomy 21, which means each cell in the body has three copies of chromosome 21 instead of the usual two copies. […] Less commonly, Down syndrome occurs when part of chromosome 21 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) in a parent or very early in fetal development. Affected people have two normal copies of chromosome 21 plus extra material from chromosome 21 attached to another chromosome, resulting in three copies of genetic material from chromosome 21. Affected individuals with this genetic change are said to have translocation Down syndrome.

• #6 About Down Syndrome | National Down Syndrome Society (NDSS)

  https://ndss.org/about

  Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21. […] This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. […] Down syndrome is usually caused by an error in cell division called nondisjunction. Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. […] Regardless of the type of Down syndrome, a person may have, all people with Down syndrome have an extra, critical portion of chromosome 21 present in all or some of their cells. […] The cause of the extra full or partial chromosome is still unknown. […] There is no definitive scientific research that indicates that Down syndrome is caused by environmental factors or the parents activities before or during pregnancy.

• #6 About Down Syndrome | National Down Syndrome Society (NDSS)

  https://ndss.org/about

  The additional partial or full copy of the 21st chromosome which causes Down syndrome can originate from either parent. Approximately 5% of the cases have been traced to the father. […] In translocation, which accounts for about 3% of cases of Down syndrome, the total number of chromosomes in the cells remains 46; however, an additional full or partial copy of chromosome 21 attaches to another chromosome, usually chromosome 14.

• #7 Down syndrome – Wikipedia

  https://en.wikipedia.org/wiki/Down_syndrome

  Translocation Down syndrome is another rare type. […] The cause of the extra full or partial chromosome is still unknown. Most of the time, Down syndrome is caused by a random mistake in cell division during early development of the fetus, but not inherited, and there is no scientific research which shows that environmental factors or the parents’ activities contribute to Down syndrome. […] The only factor that has been linked to the increased chance of having a baby with Down syndrome is advanced parental age. This is mostly associated with advanced maternal age but about 10 per cent of cases are associated with advanced paternal age. […] Down syndrome is caused by having three copies of the genes on chromosome 21, rather than the usual two. […] The extra chromosome content can arise through several different ways. The most common cause (about 92-95% of cases) is a complete extra copy of chromosome 21, resulting in trisomy 21.

• #8 Trisomy 21 Causes Down Syndrome | Learn Science at Scitable

  http://www.nature.com/scitable/topicpage/trisomy-21-causes-down-syndrome-318

  Currently, Down syndrome (DS) is one of the most common birth defects, affecting about one in every 750 live births. […] Then, in the 1950s, researchers finally determined the source of DS: the presence of an extra copy of chromosome 21, a condition often referred to as trisomy 21. […] Trisomy 21 is now accepted to be the major cause of DS, accounting for about 95% of cases. […] Since the late 1950s, scientists have also determined that a smaller number of DS cases (roughly 5%) are caused by chromosomal translocations. […] In these cases, a segment of chromosome 21 is transferred to a second chromosome, usually chromosome 14 or 15. […] Robertsonian translocation, for example, is one of many different types of translocation that cytogeneticists have identified in DS patients over the years.

• #9 Down Syndrome (Trisomy 21) – Pediatrics – Merck Manual Professional Edition

  https://www.merckmanuals.com/professional/pediatrics/chromosome-and-gene-abnormalities/down-syndrome-trisomy-21

  Down syndrome is an abnormality of chromosome 21 that can cause intellectual disability, microcephaly, short stature, and characteristic facies. […] In approximately 95% of cases, Down syndrome is caused by nondisjunction resulting in an extra chromosome 21 (trisomy 21), which is typically maternally derived. […] Approximately 4% of Down syndrome cases are due to a translocation. […] The most common translocation is t(14;21), in which chromosome 21 is attached to chromosome 14; this is an unbalanced translocation, resulting in a chromosome count of 45. […] Theoretically, the chance that a carrier mother will have a child with Down syndrome is 1:3, but the actual risk is lower (approximately 1:10). […] If the father is the carrier, the risk is only 1:20. […] Translocation 21q;21q, which occurs when the extra chromosome 21 is attached to another chromosome 21, is much less common. […] Down syndrome mosaicism presumably results from nondisjunction during cell division in the embryo. […] If a parent has germline mosaicism for trisomy 21, an increased risk, above the maternal age-based risk, exists for a second affected child.

• #10 Down Syndrome – Causes, Symptoms, Treatment, Diagnosis – MedBroadcast.com

  https://medbroadcast.com/condition/getcondition/down-syndrome

  Down syndrome is a genetic condition caused by the presence of an extra whole chromosome, or part of a chromosome, specifically chromosome 21. […] According to the NDSS and the National Association for Down Syndrome (NADS), there is no connection between any type of Down syndrome and parents’ activities before or during pregnancy. […] The most common type of Down syndrome is trisomy 21, which accounts for 95% of all cases. In this type of Down syndrome, abnormal cell division results in an extra chromosome 21 in each cell. […] At present, researchers are not sure what causes the presence of an extra chromosome 21. […] Other less common forms of Down syndrome result from other processes occurring during cell division, which result in an extra partial chromosome.

• #11 Down Syndrome | Birth Defects | CDC

  https://www.cdc.gov/birth-defects/about/down-syndrome.html

  Down syndrome is a genetic condition where a person is born with an extra chromosome. […] Down syndrome is a condition in which a person has an extra copy of chromosome 21. Chromosomes are small „packages” of genes in the body’s cells, which determine how the body forms and functions. […] When babies are growing, the extra chromosome changes how their body and brain develop. This can cause both physical and mental challenges. […] We do not know for sure why Down syndrome occurs or how many different factors play a role. […] One factor is your age when you get pregnant. The risk of having a baby with Down syndrome increases with age. This is especially the case if you are 35 years or older when you get pregnant. […] Parents with one child with Down syndrome have a higher chance of having another child with Down syndrome regardless of age. […] Ghosh S, Feingold E, Dey SK. Etiology of Down syndrome: Evidence for consistent association among altered meiotic recombination, nondisjunction, and maternal age across populations.

• #12 Down Syndrome: Causes, Types, and Symptoms

  https://www.healthline.com/health/down-syndrome

  Down syndrome results from an extra copy of the 21st chromosome. […] This extra chromosome causes problems as the brain and physical features develop. […] In children with Down syndrome, one of the chromosomes doesn’t separate properly. […] According to the National Down Syndrome Society (NDSS), about 1 in 700 babies in the United States is born with Down syndrome. […] Certain parents have a greater chance of giving birth to a child with Down syndrome. […] The probability increases the older the mother is. […] Research shows that paternal age also has an effect. […] Other parents who are more likely to have a child with Down syndrome include people with a family history of Down syndrome and people who carry the genetic translocation.

• #13 Down Syndrome Causes and Risk Factors

  https://www.everydayhealth.com/down-syndrome/causes-risk-factors-babies/

  In a small number of people with Down syndrome cases less than 4 percent the child receives only a partial extra copy of the 21st chromosome. This is called translocation, which occurs when all or part of the 21st chromosome is stuck to another chromosome. […] In very rare cases (less than 1 percent), the extra chromosome is not present in every cell of the childs body this is called mosaicism. […] While experts understand whats going on inside the cells of a person with Down syndrome, they dont have a good explanation for what causes these genetic abnormalities to occur in the first place. […] In the majority of Down syndrome cases, the errors in cell division that lead to the extra 21st chromosome come from the childs mother. […] As maternal age increases, risk for Down syndrome increases, Heller says.

• #13 Down Syndrome Causes and Risk Factors

  https://www.everydayhealth.com/down-syndrome/causes-risk-factors-babies/

  While a mothers age is a well-established risk factor for Down syndrome, the vast majority of children with Down syndrome are born to women who are younger than 35. […] There is some research tying specific gene variations to Down syndrome. […] A shortage of folate a type of B vitamin has been shown to disrupt the way DNA and chromosomes separate and recombine. […] Its possible that a person can carry translocated genetic material. […] If a baby is born to a mother with Down syndrome, there is a 35 to 50 percent chance the child will inherit the condition or another developmental disability. […] As of today, there is nothing a woman can do to lower her odds of having a child with Down syndrome apart from choosing to have children at a younger age.

• #14 Down Syndrome – familydoctor.org

  https://familydoctor.org/condition/down-syndrome/

  Translocation Down syndrome. Translocation (or shift) occurs before or at conception when part of chromosome 21 attaches onto another chromosome. It is the only form of Down syndrome that can be passed down from parent to child. This can happen even if the parent shows no symptoms of Down syndrome. […] There are factors that increase your risk of having a child with Down syndrome: Advanced maternal age. The older the woman is, the older her eggs are. Older eggs are more likely to divide abnormally. At age 35, your risk of having a baby with Down syndrome is about 1 in 350. At age 40, the risk is 1 in 100. By age 45, your risk is 1 in 30. […] Already having a child with Down syndrome. If you have a baby with Down syndrome, you have a 1 in 100 chance of having another one. […] Being a carrier of a chromosomal abnormality. Both men and women can carry the translocation abnormality. If you are a carrier, you risk passing it on to your child.

• #15 Causes and Statistics

  https://cmdss.org/parent-guide/about-down-syndrome/causes-statistics/

  Regardless of the type of Down syndrome a person may have, all people with Down syndrome have an extra, critical portion of chromosome 21 present in some or all of their cells. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. […] The cause of the extra full or partial chromosome is still unknown. Maternal age is the only factor that has been linked to an increased chance of having a baby with Down syndrome resulting from nondisjunction or mosaicism. However, due to higher birth rates in younger women, 80% of children with Down syndrome are born to women under 35 years of age. […] There is no definitive scientific research that indicates that environmental factors or parents activities cause Down syndrome. […] The additional partial or full copy of the 21st chromosome which causes Down syndrome can originate from either the father or the mother. Approximately 5% of the cases are traceable to the father.

• #15 Causes and Statistics

  https://cmdss.org/parent-guide/about-down-syndrome/causes-statistics/

  All 3 types of Down syndrome are genetic conditions (relating to the genes). Only 1% of all cases of Down syndrome have a hereditary component (passed from parent to child through the genes). Heredity is not a factor in trisomy 21 (nondisjunction) and mosaicism. However, in one third of cases of Down syndrome resulting from translocation there is a hereditary component. This accounts for about 1% of all cases of Down syndrome. […] The age of the mother does not seem to be linked to the risk of translocation. Most cases are sporadic chance events. However, in about one third of cases, one parent is a carrier of a translocated chromosome.

• #16 Understanding Down Syndrome: Causes, Types, and Management

  https://www.medlineacademics.com/blog/down-syndrome.php

  Advanced Maternal age is one of the risk factors for having a baby with Down syndrome because as the egg undergoes the aging process, its capacity to divide properly during cell division decreases. After the age of 35, the risk of Down syndrome is significantly high. […] When a couple gives birth to a child with Downs syndrome, the chances of having another baby with the same condition is 1 in 100 until the age of 40. […] The risk of having a second child with Downs syndrome after the first depends on which parent is the carrier. If the mother is the carrier, there is a 10-15% chance of recurrence of translocation and if the father is the carrier, there is a 3% chance of recurrence.

• #17 The link between family health history and Down syndrome | March of Dimes

  https://www.marchofdimes.org/find-support/blog/link-between-family-health-history-and-down-syndrome

  Down syndrome (also called trisomy 21) is the most common chromosomal condition in the United States. […] What causes Down syndrome? […] Babies with Down syndrome have an extra copy of chromosome 21. This extra copy changes the way the brain and body develop. […] We dont know for sure why Down syndrome happens, but these things can affect your risk of having a baby with the condition: […] Your risk of having a baby with Down syndrome increases as you get older, especially if you are age 35 or older. […] If you or your partner are a carrier of translocation Down syndrome, you carry a gene change for the condition, but you dont actually have Down syndrome. […] If you already have a baby with Down syndrome, your risk for having another is higher.

• #18

• #18 “Down syndrome: an insight of the disease” | Journal of Biomedical Science | Full Text

  https://jbiomedsci.biomedcentral.com/articles/10.1186/s12929-015-0138-y

  A critical region within 21q22 was believed to be responsible for several DS phenotypes including craniofacial abnormalities, congenital heart defects of the endocardial cushions, clinodactyly of the fifth finger and mental retardation. […] The various clinical conditions associated with DS are Alzheimers disease, heart defects, leukemia, hypertension and gastrointestinal problems. […] DS patients have greatly increased risk of early onset AD. […] The incidence of CHD in newborn babies with DS is up to 50%. […] Patients with DS display a unique spectrum of malignancies, which include leukemias as well as solid tumors. […] People with DS have been reported to have a reduced incidence of hypertension. […] DS patients constitute ~12% of all cases of HD.

• #19 Gene behind Down syndrome heart defects identified | UCL News – UCL – University College London

  https://www.ucl.ac.uk/news/2024/jan/gene-behind-down-syndrome-heart-defects-identified

  A gene that causes heart defects in Down syndrome has been identified by researchers at UCL and the Francis Crick Institute. […] Down syndrome affects around 1 in 800 new births and is caused by an extra third copy of chromosome 21. […] Consequently, better treatment options are needed, and this must be guided by knowledge of which of the extra 230 genes on chromosome 21 are responsible for the heart defects. […] Using genetic mapping, the researchers identified a gene on human chromosome 21 called Dyrk1a, which causes heart defects when three copies of the gene are present in the mouse model of Down syndrome. […] An extra copy of Dyrk1a turned down the activity of genes required for cell division in the developing heart and the function of the mitochondria, which produce energy for the cells.

• #19 Gene behind Down syndrome heart defects identified | UCL News – UCL – University College London

  https://www.ucl.ac.uk/news/2024/jan/gene-behind-down-syndrome-heart-defects-identified

  The team found that while three copies of Dyrk1a is required to cause heart defects in mice, another unknown gene is also involved. […] Our research shows that inhibiting DYRK1A can partially reverse changes in mouse hearts, suggesting that this may be a useful therapeutic approach. […] It was remarkable that just restoring the copy number of one gene from three to two reversed the heart defects in the mouse model for Down syndrome. […] Even though Dyrk1a isn’t the only gene involved, it’s clearly a major player in many different aspects of Down syndrome.

• #20 The etiology of Down syndrome: Maternal MCM9 polymorphisms increase risk of reduced recombination and nondisjunction of chromosome 21 during meiosis I within oocyte | PLOS Genetics

  https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1009462

  The etiology of Down syndrome: Maternal MCM9 polymorphisms increase risk of reduced recombination and nondisjunction of chromosome 21 during meiosis I within oocyte […] Altered patterns of recombination on 21q have long been associated with the nondisjunction chromosome 21 within oocytes and the increased risk of having a child with Down syndrome. […] We observed that twenty-five out of forty-one single nucleotide polymorphic sites within MCM9 exhibited an association with meiosis I error (N = 700), but not with meiosis II error (N = 125). […] Maternal age stratified characterization of cases revealed that MCM9 risk variants were associated with an increased chance of reduced recombination on 21q within oocytes. […] We hypothesize that the polymorphisms in MCM9 predispose women to experience reduced recombination on chromosome 21 in oocytes at meiosis I, which ultimately leads to the birth of a child with Down syndrome.

• #20 The etiology of Down syndrome: Maternal MCM9 polymorphisms increase risk of reduced recombination and nondisjunction of chromosome 21 during meiosis I within oocyte | PLOS Genetics

  https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1009462

  The risk of NDJ increases gradually with age due to the rapid degradation of protein machinery that includes sister chromatid cohesins and the surveillance system. […] We have selected MCM9 to characterize its polymorphisms as the underlying risk factors of recombination errors on Ch21, considering previous reports on its association with ovarian insufficiency, compromised fertility, and genomic instability in humans and model organisms. […] We observed a strong association of all twenty-five risk variants only with the MI error, and not with the MII error. […] We can only infer that the polymorphic sites exhibit a strong association with each other and impart risk for MI errors and the occurrence of these three genotypes among the women was probably stochastic. […] We report, for the first time, that polymorphic variants of the recombination and DNA repair regulator helicase MCM9 gene are associated with an increased risks for recombination failure in meiosis and most MI errors involving Ch21.

• #21

  https://www.nhs.uk/conditions/downs-syndrome/

  Down’s syndrome is when you’re born with an extra chromosome. […] You usually get an extra chromosome by chance, because of a change in the sperm or egg before you’re born. […] This change does not happen because of anything anyone did before or during pregnancy. […] In almost all cases, Down’s syndrome does not run in families. […] Your chance of having a baby with Down’s syndrome increases as you get older, but anyone can have a baby with Down’s syndrome.

• #22 Commentary: „The Etiology of Down Syndrome”

  https://www.humangeneticsjournal.com/articles/commentary-the-etiology-of-down-syndrome.html

  It is well known that most Down Syndrome cases are of maternal origin, and that the likelihood of having a child with Trisomy 21 increases with maternal age. […] In sharp contrast, the underlying mechanism and origin of the extra chromosome 21 in DS has been a matter of debate for a long time. It has become generally accepted that the major cause is a faulty maternal reductional/meiotic cell division that occurs post-puberty at the monthly ovulation. […] Our research group has instead focused attention on a totally different process, giving rise to oocytes with 24 chromosomes. We have tested the possibility that the extra chromosome 21 may be due to a segregation problem, taking place much earlier than post-puberty meiosis, i.e. during fetal mitotic oogonial cell divisions. […] Substantial statistical support for the mitotic oogonial etiology of T21 has recently been presented by Hornyi et al., i.e. that women, who have used oral contraception pills at young age, have a reduced likelihood of begetting a child with DS at later reproductive age. The implication of this observation is the differentiation between the two alternatives for the etiology of T21 DS, invalidating the meiotic one, which is based on premature loss of centromeric cohesion as the major source of aneuploidy in oocytes from older women, because it is hardly conceivable that use of contraceptives at young age would prevent depletion of oocyte chromosomal cohesins in ageing ovaries.

• #23 Facts, Myths, & Truths About Down Syndrome | National Down Syndrome Society (NDSS)

  https://ndss.org/myths-truths

  Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. […] Translocation, a type of Down syndrome that accounts for 3 to 4% of all cases, is the only type of Down syndrome known to have a hereditary component. Of those, one third (or 1% of all cases of Down syndrome) are hereditary. […] The likelihood of having a child with Down syndrome increases with the age of the mother, especially after age 35. […] Though we know that an extra full or partial copy of chromosome 21 causes the characteristics of Down syndrome, researchers are making great strides in identifying how individual genes on chromosome 21 affect a person with Down syndrome. Scientists now feel strongly that it will be possible to improve, correct, or prevent many of the health problems associated with Down syndrome in the future.

• #24 Down Syndrome (Trisomy 21) – Children’s Health Issues – MSD Manual Consumer Version

  https://www.msdmanuals.com/home/children-s-health-issues/chromosome-and-gene-abnormalities/down-syndrome-trisomy-21

  Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. […] Down syndrome is caused by an extra chromosome 21. […] Trisomy 21 causes about 95% of the cases of Down syndrome. Thus, most people with Down syndrome have 47 chromosomes instead of the normal 46. However, about 4% of people with Down syndrome have 46 chromosomes, but the extra chromosome 21 is attached to another chromosome, creating an abnormal, but not extra, chromosome. This abnormal attachment is called translocation. […] The extra chromosome usually comes from the mother, and a couple’s risk of having a baby with an extra chromosome gradually increases with the mother’s age. […] Women who have Down syndrome have a 50% chance of having a child with Down syndrome. […] There is no cure for Down syndrome. However, some specific symptoms and problems caused by the syndrome can be treated.

• #25 Down Syndrome | Boston Children’s Hospital

  https://www.childrenshospital.org/conditions/down-syndrome

  Down syndrome is a common genetic condition that occurs when a child has an extra copy of chromosome 21. […] In Down syndrome, a change occurs during cellular division such that the egg or sperm has an extra chromosome 21. Researchers are still unsure of what causes the cells to divide in this manner (though the chance of this happening increases with increasing maternal age). […] This extra genetic material causes the health and developmental issues of Down syndrome.

• #26 Health Complications Linked to Down Syndrome

  https://www.everydayhealth.com/down-syndrome/complications-health-problems/

  Down syndrome is a genetic condition that results when a person is born with 47 chromosomes in their cells instead of the usual 46. (1) That extra chromosome affects the way the person develops both physically and cognitively throughout childhood and affects adulthood. The genetic condition is also linked to several other health conditions. […] Down syndrome is defined as being born with extra genetic material (an extra full or partial copy of chromosome 21). This extra genetic material can alter the way brain cells function, which puts people with Down syndrome at increased risk of developing Alzheimers disease. […] Hypothyroidism, or an underactive thyroid, is common among people with Down syndrome and affects up to 7 percent of children and between 39 and 61 percent of adults with Down syndrome. (8)

• #26 Health Complications Linked to Down Syndrome

  https://www.everydayhealth.com/down-syndrome/complications-health-problems/

  People with Down syndrome are also at an elevated risk for developing leukemia. […] The extra chromosome doesnt bring only problems. Vellody says there are a number of health benefits associated with it, too. People with Down syndrome tend not to get solid organ tumors, he says. So we think about lung cancer, brain cancer, and liver cancer these are things adults in the general population can get. But people with Down syndrome dont tend to get them. […] There’s something protective on the 21st chromosome, Vellody says.

• #27 Down Syndrome: Causes, Symptoms, Life Expectancy, & Tests

  https://www.emedicinehealth.com/down_syndrome/article_em.htm

  It is now well known that the extra genes on the additional chromosome 21 are the cause of Down syndrome. […] Scientists are trying to determine which of the genes on chromosome 21 cause different characteristics of the disorder when present in three copies. […] Currently, about 400 genes on chromosome 21 have been identified, but the function of most remains unknown. […] Advanced maternal age is the only known risk factor for Down syndrome. […] The average brain volume of a person with Down syndrome is small and certain brain structures such as the hippocampus and the cerebellum do not function properly. […] Scientists are trying to find out which genes on the extra chromosome 21 affect cognition in Down syndrome.

• #28 Down Syndrome and Alzheimer’s | Symptoms & Treatments | alz.org

  https://www.alz.org/alzheimers-dementia/what-is-dementia/types-of-dementia/down-syndrome

  As they age, those affected by Down syndrome have a greatly increased risk of developing a type of dementia that’s either the same as or very similar to Alzheimer’s disease. […] Scientists think that the increased risk of dementia like other health issues associated with Down syndrome results from the extra genes present. One of the chromosome 21 genes of greatest interest in the Down syndrome/Alzheimer’s connection codes amyloid precursor protein (APP). Scientists don’t yet know APP’s function, but they’ve learned that day-to-day brain activity involves continuous „processing” of APP into shorter pieces. One of the brain’s APP processing pathways produces beta-amyloid, a fragment that’s the chief component of plaques and a prime suspect in Alzheimer’s-related brain changes. Having an extra copy of the APP gene may increase production of beta-amyloid, triggering the chain of biological events leading to Alzheimer’s. […] The fact that APP is strongly implicated in Alzheimer’s through two different mechanisms one involving a whole extra copy of the normal gene and the other involving specific minor changes in the genes chemical code makes the intersection of Down syndrome and Alzheimer’s a strong focus of research.

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