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• #1 Turner syndrome // Middlesex Health

  https://middlesexhealth.org/learning-center/diseases-and-conditions/turner-syndrome

  Turner syndrome, a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing. […] In females who have Turner syndrome, one copy of the X chromosome is missing, partially missing or changed. […] The genetic changes of Turner syndrome may be one of the following: Monosomy. The complete absence of an X chromosome generally occurs because of an error in the father’s sperm or in the mother’s egg. This results in every cell in the body having only one X chromosome. […] Mosaicism. In some cases, an error occurs in cell division during early stages of fetal development. This results in some cells in the body having two complete copies of the X chromosome. Other cells have only one copy of the X chromosome. […] X chromosome changes. Changed or missing parts of one of the X chromosomes can occur. Cells have one complete and one altered copy. This error can occur in the sperm or egg with all cells having one complete and one altered copy. Or the error can occur in cell division in early fetal development so that only some cells contain the changed or missing parts of one of the X chromosomes (mosaicism).

• #2 Turner Syndrome: What It Is, Causes, Symptoms & Treatment

  https://my.clevelandclinic.org/health/diseases/15200-turner-syndrome

  Turner syndrome happens when a female baby is born with one missing or partial X chromosome. […] Turner syndrome (TS) is a congenital condition (present from birth) that only affects females. It happens when one of two of the X chromosomes is missing, either partially or completely. […] Turner syndrome happens when one of a babys two X chromosomes is missing or incomplete. Researchers dont yet understand why this happens. […] About 45% of people with TS have monosomy X. The chromosomal abnormality happens randomly during the formation of reproductive cells (eggs or sperm) in the affected persons biological parent. If one of these atypical reproductive cells contributes to the genetic makeup of a fetus during conception, the baby will have a single X chromosome in each cell at birth. […] Some of your childs cells have a pair of X chromosomes, while other cells only have one. It happens randomly during cell division early in pregnancy. […] In rare cases, babies may have inherited TS, meaning their biological parent was born with it and passed it on. This type usually happens because of a missing part of the X chromosome.

• #2 Turner syndrome: Symptoms, causes, and treatment

  https://www.medicalnewstoday.com/articles/176083

  Turner syndrome is a chromosomal disorder that affects only females. It involves a lack of part or all of a second sex chromosome in some or all cells. […] When a female has TS, one X chromosome copy is either absent or significantly altered. […] A number of genetic alterations are possible in TS. […] Monosomy: One X chromosome is completely missing. Experts believe this is caused by an error either in the fathers sperm or the mothers egg. Every cell in the offsprings body has one X chromosome missing. […] Mosaic Turner syndrome, also called mosaicism or Turner mosaicism: During the early stages of fetal development, an error may occur in cell division, resulting in some cells having two X chromosome copies, while others only have one. Sometimes, there may be some cells with both X chromosome copies, and others with one altered copy.

• #3 Turner Syndrome – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK554621/

  Turner syndrome results from a deletion or the non-functioning of one X chromosome in females. About half of the population with Turner syndrome have monosomy X (45,XO). The other 50% of the population has a mosaic chromosomal component (45,X with mosaicism). […] Some types of anomalies in the X chromosome that can lead to a nonfunctioning X chromosome are as follows: Isochromosome Xq, where there are two copies of the long arm of the chromosome that are connected head to head. Ring chromosome, where a part of the ends of short and long arms of the X chromosome is missing. Xp or Xq deletion, where the deletion of part of the short arm of the X chromosome takes place. […] Some patients with Turner syndrome can have a Y chromosome mosaicism. Although not a cause of Turner syndrome, the SHOX (short stature homeobox-containing gene on the X- chromosome) is associated with the short stature found in Turner syndrome. Turner syndrome is usually not inherited but is a random event during reproduction.

• #4 Turner syndrome: Symptoms, causes, and treatment

  https://www.medicalnewstoday.com/articles/176083

  Turner syndrome is a chromosomal disorder that affects only females. It involves a lack of part or all of a second sex chromosome in some or all cells. […] When a female has TS, one X chromosome copy is either absent or significantly altered. […] A number of genetic alterations are possible in TS. […] Monosomy: One X chromosome is completely missing. Experts believe this is caused by an error either in the fathers sperm or the mothers egg. Every cell in the offsprings body has one X chromosome missing. […] Mosaic Turner syndrome, also called mosaicism or Turner mosaicism: During the early stages of fetal development, an error may occur in cell division, resulting in some cells having two X chromosome copies, while others only have one. Sometimes, there may be some cells with both X chromosome copies, and others with one altered copy.

• #5 Turner syndrome: Clinical manifestations and diagnosis – UpToDate

  https://www.uptodate.com/contents/turner-syndrome-clinical-manifestations-and-diagnosis

  Turner syndrome (TS) is a sex chromosome disorder that affects phenotypic females with one intact X chromosome and complete or partial absence of the second sex chromosome in association with one or more specific clinical manifestations. It is one of the more commonly occurring chromosomal aneuploidies. […] Most individuals with TS have a karyotype consisting of only 45,X cells (monosomy X). Approximately one-half of all patients with TS have mosaic genotypes. In these cases, 45,X cells co-occur with cells containing other chromosome complements (eg, 45,X/46,XX or 45,X/47,XXX) or abnormally rearranged X chromosomes. These structural abnormalities are described using the following notation: Partial deletion of an X chromosome: del(p22.3).

• #6 Turner syndrome // Middlesex Health

  https://middlesexhealth.org/learning-center/diseases-and-conditions/turner-syndrome

  Y chromosome material. In a small percentage of Turner syndrome cases, some cells have one copy of the X chromosome and other cells have one copy of the X chromosome and some Y chromosome material. These individuals develop biologically as female, but the presence of Y chromosome material increases the risk of developing a type of cancer called gonadoblastoma. […] The missing or changed X chromosome of Turner syndrome causes problems during fetal development and other developmental problems after birth for example, short stature, ovarian insufficiency and heart defects.

• #7 What is Turner Syndrome? And Why Does It Affect Only Females?

  https://www.webmd.com/children/what-is-turner-syndrome

  These can happen when your cells have one complete copy and one abnormal or missing copy of the X chromosome. […] In a few cases, some cells get one copy of the X chromosome, while other cells get one copy of the X chromosome and some Y chromosome material. Biologically, you develop as a female. The Y chromosome material increases your risk of a type of cancer called gonadoblastoma.

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

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

  Turner syndrome occurs when part or all of an X chromosome is missing from most or all of the cells in a girls body. […] The error that leads to the missing chromosome appears to happen during the formation of the egg or sperm. […] Most commonly, a girl with Turner syndrome has only one X chromosome. […] Because she is missing part or all of a chromosome, certain genes are missing. The loss of these genes leads to the symptoms of Turner syndrome. […] Sometimes, girls with Turner syndrome have some cells that are missing one X chromosome (45,X) and some that are normal. […] This condition is called mosaicism (pronounced moh-ZEY-uh-siz-uhm). If the second sex chromosome is lost from most of a girls cells, then its likely that she will have symptoms of Turner syndrome. If the chromosome is missing from only some of her cells, she may have no symptoms or only mild symptoms.

• #9 Turner syndrome: Symptoms, causes, and treatment

  https://www.medicalnewstoday.com/articles/176083

  The loss or abnormality of the X chromosome occurs spontaneously at conception when the egg is fertilized. The missing or altered X chromosome causes errors during fetal development and in development after birth. […] Having one child with TS does not increase the risk of having other children with the condition. […] It is thought that the risk of having TS is the same for all females, regardless of ethnicity or location. It occurs randomly, it is not associated with parental age, and there are no known toxins or environmental factors that appear to affect the risk.

• #10 Turner syndrome – Wikipedia

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

  Turner syndrome is caused by one X chromosome (45,X), a ring X chromosome, 45,X/46,XX mosaicism, or a small piece of the Y chromosome in what should be an X chromosome. […] The abnormal cells may have only one X (monosomy) (45,X) or they may be affected by one of several types of partial monosomy like a deletion of the short p arm of one X chromosome (46,X,del(Xp)) or the presence of an isochromosome with two q arms (46,X,i(Xq)). […] In the majority of cases where monosomy occurs, the X chromosome comes from the mother. […] This may be due to a nondisjunction in the father. […] Meiotic errors that lead to the production of X with p arm deletions or abnormal Y chromosomes are also mostly found in the father. […] Isochromosome X or ring chromosome X on the other hand are formed equally often by both parents. […] Overall, the functional X chromosome usually comes from the mother.

• #11 Turner syndrome | Endocrine Conditions

  https://www.yourhormones.info/endocrine-conditions/turner-syndrome/

  Turner syndrome is a genetic disorder due to having only one of the usual two female X sex chromosomes (XO rather than XX). […] An abnormality in one of the two X chromosomes in girls causes Turner syndrome. In around 50% of cases there is an entire X chromosome missing, or parts of the chromosome may be missing or rearranged. […] The cause is unknown, but it occurs very early in foetal life. […] In the vast majority of girls, there are no other affected family members. One of each chromosome pair comes from either parent and in 80% of cases, the missing X-chromosome comes from the father.

• #12 What is Turner syndrome? Its causes, characteristics and pregnancy

  https://www.invitra.com/en/turner-syndrome/

  Turner syndrome is a chromosomal alteration characterized by a complete or partial loss of one of the sex chromosomes in the female sex. As a result, the karyotype of those women is 45,XO instead of the usual karyotype 46,XX. […] The main cause of Turner syndrome is the complete or, as explained above, partial absence of an X sex chromosome. The exact mechanism that leads to this genetic alteration in embryos is unknown, but two possible theories are currently being considered: Meiosis the cause would be an alteration in the gametogenesis (formation of eggs and sperm) of the parents. This would result in gametes that do not carry the X chromosome and that, when fertilized, would result in embryos with karyotype 45,XO. Mitosis the loss of the X chromosome would not take place in the gametes but would get lost due to a failure in the first embryonary divisions after the fertilisation. […] The majority of researches support this second theory, the mitotic one, although they do not completely dismiss the first one.

• #13 Turner Syndrome: Diagnosis and Management | AAFP

  https://www.aafp.org/pubs/afp/issues/2007/0801/p405.html

  Turner syndrome is caused by a reduced complement of genes that are typically expressed from both X chromosomes in females. Normally one X chromosome is randomly inactivated during the first week of life (when there are fewer than 200 embryonic cells); therefore, it may seem paradoxical that having a single X chromosome would cause clinical consequences. However, not all genes from the second chromosome are inactivated in Turner syndrome. Some genes escape X-inactivation via a process initiated by the X-inactivation-specific transcript (XIST) gene that is transcribed exclusively from the inactive genes. The loss of these noninactivated X genes causes the phenotypic manifestations characteristic of Turner syndrome, such as short stature. […] Turner syndrome occurs in one out of 2,500 to 3,000 live female births; however, many more 45,X conceptuses do not survive past the first trimester. Ninety-nine percent of conceptuses with a 45,X karyotype abort spontaneously; Turner syndrome causes 10 percent of all first-trimester miscarriages. Unlike with Down syndrome, maternal age does not increase the risk of Turner syndrome, and there are no clearly established risk factors. Recurrence in subsequent pregnancies is rare.

• #14 The role of the SHOX gene in the pathophysiology of Turner syndrome | Endocrinología y Nutrición (English Edition)

  https://www.elsevier.es/en-revista-endocrinologia-nutricion-english-edition–412-articulo-the-role-shox-gene-in-S2173509311000286

  Turner syndrome (TS) affects 1:2500 live females. It is caused by partial or complete absence of a sex chromosome. Patients with deletions of the distal segment of the short arm of X chromosome (Xp-) including haploinsufficiency of the SHOX (short stature homeobox) have, more often, short stature, skeletal abnormalities and hearing impairments. […] The genetic anomaly is determined by the absence of genes on the X chromosome. That is, the TS phenotype can be determined by a haploinsufficiency of genes bound to the X chromosome that escapes inactivation. […] Patients with TS and deletions at the end of the short arm of X-chromosome (Xp-), including haploinsufficiency of the SHOX gene (short stature homeobox), have short stature and orthopedic abnormalities (e.g.: cubitus valgus, Madelung deformity, micrognatia, and high-arched palate) and hearing impairment.

• #15 About Turner Syndrome

  http://www.genome.gov/Genetic-Disorders/Turner-Syndrome

  Turner syndrome is a chromosomal condition related to the X chromosome. […] Researchers have not yet determined which genes on the X chromosome are responsible for most signs and symptoms of Turner syndrome. They have, however, identified one gene called SHOX that is important for bone development and growth. Missing one copy of this gene likely causes short stature and skeletal abnormalities in women with Turner syndrome. […] Turner syndrome occurs when one of the two X chromosomes normally found in women is missing or incomplete. Although the exact cause of Turner syndrome is not known, it appears to occur as a result of a random error during the formation of either the eggs or sperm. […] In Turner syndrome, the girl does not have the usual pair of two complete X chromosomes. The most common scenario is that the girl has only one X chromosome in her cells. Some girls with Turner syndrome do have two X chromosomes, but one of the X chromosomes is incomplete. In another scenario, the girl has some cells in her body with two X chromosomes, but other cells have only one. This is called mosaicism.

• #16 Turner Syndrome Clinical Presentation: History, Physical, Causes

  https://emedicine.medscape.com/article/949681-clinical

  Patients with Turner syndrome may present with a cystic hygroma on a fetal ultrasound or may have swollen hands and feet owing to lymphedema at birth. […] The diagnosis of Turner syndrome requires the presence of typical phenotypic features and the complete or partial absence of a second sex chromosome. […] In patients with a single X chromosome, the chromosome is of maternal origin in two thirds of cases. […] Many of the features of Turner syndrome, including the short stature, are due to the lack of a second SHOX gene, which is on the X chromosome.

• #17 Turner Syndrome where are we? | Orphanet Journal of Rare Diseases | Full Text

  https://ojrd.biomedcentral.com/articles/10.1186/s13023-024-03337-0

  Turner Syndrome (TS) is a chromosomal disorder characterized by the partial or total loss of one of the two X-chromosomes in female cells due to sporadic nondisjunction. […] The exact cause remains incompletely understood. However, it is believed to result from both genomic imbalances induced by sex chromosome genes and the additive effect of epigenetic factors on linked genes within gene networks. […] The short stature homeobox-containing gene (SHOX) regulates growth, and its haploinsufficiency contributes to the characteristic short stature in TS. […] TS is primarily not inherited, with most cases involving monosomy involving the mothers X chromosome. […] However, if a balanced translocation occurs or if the mother has 45, X mosaicism is restricted to her germ cells. […] In rare cases, partial deletion of the X chromosome can result in TS inheritance by the next generation.

• #18 The role of the SHOX gene in the pathophysiology of Turner syndrome | Endocrinología y Nutrición (English Edition)

  https://www.elsevier.es/en-revista-endocrinologia-nutricion-english-edition–412-articulo-the-role-shox-gene-in-S2173509311000286

  The high frequency of repetitions in the PAR1 region makes this genomic region more prone to recombination and that is why the deletions are found in 70% of the affected individuals. […] Turner syndrome is almost always associated with the loss of one SHOX gene because of the numerical or structural aberration of the X chromosome associated with this syndrome. The loss of both SHOX alleles causes the complete lack of SHOX and an extreme phenotype of osteodysplasia called Langer syndrome. […] The deficiency of the SHOX gene seems to be one of the main causes of short stature in patients with Leri-Weill syndrome (LWS), Langer mesomelic dysplasia and also of proportional short stature in patients with isolated short stature. […] Most TS individuals have only two copies of the SHOX gene. Nevertheless, the haploinsufficiency of the SHOX gene does not explain all the anomalies in TS, suggesting that other genes take part in this process.

• #19 Epigenetics in Turner syndrome | Clinical Epigenetics | Full Text

  https://clinicalepigeneticsjournal.biomedcentral.com/articles/10.1186/s13148-018-0477-0

  Evidence collected in recent years does not seem to indicate only one proposed mechanism to explain the clinical findings and the associated complications in TS, but instead the concurrence of several of them. […] A unifying hypothesis to help explain the findings in the embryonic, fetal, neonatal, and adolescent periods, as well as in adulthood, and the pathogenesis of this disorder, relates to changes in DNA conformation and its assembly without modifying its nucleotide sequence. […] The Gene Dosage Effect hypothesis is mainly supported by rare cases of partial Xp deletion, linking TS phenotypes to a small number of loci in specific segments of the Xp chromosome. […] Thus, the TS phenotype may not merely be due to genomic imbalance from deleted genes linked to the second sex chromosome but may also be due to additive influences on associated genes within a given gene network with an altered regulation of gene expression triggered by epigenetic factors.

• #20 Turner Syndrome – GenTAC Alliance

  https://www.gentacalliance.org/conditions/turner-syndrome/

  Turner syndrome (TS) is a genetic condition occurring predominantly in girls and women. It is caused by the absence of all or part of the second sex chromosome. […] While TS is a genetic condition because it involves an abnormality of a chromosome, it is typically not an inherited condition or one that runs in families. TS occurs by chance early in pregnancy and is due to the loss of a sex chromosome. This loss leaves the baby with only a single X chromosome or an X chromosome and only part of a second X chromosome (there are usually two) in each of their cells. […] Importantly, there is nothing that either parent can do before or at the start of pregnancy that will prevent or decrease the risk of having a child with TS.

• #21 What Is Turner Syndrome? Symptoms, Causes, Diagnosis, Treatment, and Prevention

  https://www.everydayhealth.com/turner-syndrome/guide/

  It’s possible, but rare, for this form of Turner syndrome to be passed from one generation to the next. […] The loss or alteration of the X chromosome that causes Turner syndrome occurs randomly sometimes as a result of problems with the father’s sperm or the mother’s egg and, for others, as a result of something that happens early in fetal development. […] In general, it’s unlikely that parents of one child with Turner syndrome will have another child with the disorder, or that any family history of the condition increases a person’s risk of developing it. […] There’s no way to prevent Turner syndrome. It’s caused by a random genetic error that leads to a missing X chromosome in the father’s sperm or the mother’s egg.

• #22 Turner syndrome

  https://dermnetnz.org/topics/turner-syndrome

  Turner syndrome develops when there is only one entire functional X chromosome. In approximately 50% of patients there is a single X chromosome ie 45,X. The other 50% may have one of a number of structural defects in the second sex chromosome. The commonest structural abnormality is called isochromosome Xq. Up to 10% have a marker (ring) X chromosome. There are some correlations between the genetic defect and the clinical presentation. 45,X is associated with the most severe clinical presentation. […] The X chromosome from the mother is found in the majority of girls with Turner syndrome. Whereas the X chromosome from the father is more commonly associated with spontaneous miscarriages. […] Turner syndrome is not associated with advanced parental age.

• #23

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

  Turner syndrome is a female-only genetic disorder that affects about 1 in every 2,000 baby girls. […] This chromosome variation happens randomly when the baby is conceived in the womb. It is not linked to the mother’s age.

• #24 Epigenetics in Turner syndrome | Clinical Epigenetics | Full Text

  https://clinicalepigeneticsjournal.biomedcentral.com/articles/10.1186/s13148-018-0477-0

  Monosomy of the X chromosome is the most frequent genetic abnormality in human as it is present in approximately 2% of all conceptions, although 99% of these embryos are spontaneously miscarried. […] Turner syndrome is due to a partial or total loss of the second sexual chromosome, resulting in the development of highly variable clinical features. […] Current studies in human and mouse models have demonstrated that this chromosomal abnormality leads to epigenetic changes, including differential DNA methylation in specific groups of downstream target genes in pathways associated with several clinical and metabolic features, mostly on autosomal chromosomes. […] Although researchers have tried to explain the clinical findings in TS based on cytogenetic and gene changes, everything seems to indicate that other causes for this disorder, beyond the nucleotide sequence of a gene or the global impact of the chromosomal imbalance, exist.

• #25 Turners Syndrome – Birth Defect Fact Sheet

  https://birthdefects.org/turners-syndrome/

  Turners Syndrome is caused by the complete or partial absence of one of the two X chromosomes. […] While it is not known what causes this, it is believed to be due to abnormalities in cell division. […] Turners Syndrome appears to be a random event that has not been associated with any environmental factors.

• #26

  https://www.exonpublications.com/index.php/exon/article/view/turner-syndrome-risk-factors-causes-symptoms-treatment

  Turner Syndrome is a genetic condition that affects females, caused by the complete or partial loss of one X chromosome. […] Turner Syndrome is not inherited and usually occurs randomly during the formation of reproductive cells or early embryonic development. […] Turner Syndrome is caused by a genetic abnormality involving the X chromosome, typically the complete or partial loss of one X chromosome. This condition is not inherited from parents but occurs as a random event during the formation of reproductive cells or early embryonic development. […] Turner Syndrome is not caused by environmental or lifestyle factors. The primary cause is a random genetic error that results in the complete or partial absence of one X chromosome. There are no known risk factors for Turner Syndrome, as it occurs unpredictably during the formation of eggs or sperm or early in embryonic development. Unlike many genetic conditions, it is not passed down from one generation to the next.

• #27 Epigenetics in Turner syndrome | Clinical Epigenetics | Full Text

  https://clinicalepigeneticsjournal.biomedcentral.com/articles/10.1186/s13148-018-0477-0

  While haploinsufficiency of genes on the X chromosome has been the focus of recent research, underlying epigenetic mechanisms have been poorly studied in TS. […] It is has become clear that epigenetic processes are altered in TS, so that by modulating gene expression, epigenetics could play a crucial role in altered growth and in the development of abnormalities of lipid and glucose metabolism associated with TS. […] The clarification of these possible causal pathways may have future implications in increasing the life expectancy of these patients and may provide informative targets for early pharmaceutical intervention.

• #28 Orphanet: Turner syndrome

  https://www.orpha.net/en/disease/detail/881

  A rare chromosomal anomaly syndrome characterized by complete or partial loss of an X chromosome in phenotypic females, clinically manifesting with short stature, primary ovarian insufficiency as well as cardiovascular, renal, liver, autoimmune diseases, hearing loss and neurocognitive abnormalities. […] X monosomy is the most common underlying etiology, while some cases have mosaicism or structural X chromosome anomalies. Clinical signs are more severe in patients with 45,X monosomy than in 45,X/46,XX or 45,X/46,XX/47,XXX mosaicism. Patients with an X isochromosome have a higher risk of liver and autoimmune diseases, while those with a ring chromosome are more prone to growth retardation and metabolic disorders. Haploinsufficiency of the SHOX gene is a well-established cause of short stature. The presence of Y material is related to the occurrence of gonadoblastoma.

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