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XX male syndrome

From Wikipedia, the free encyclopedia

XX male syndrome
Classification and external resources
Specialty	medical genetics
ICD-10	(Q98.3)
OMIM	278850
MeSH	D058531
Orphanet	393
[edit on Wikidata]

Schematic of sexual differentiation in mammals.

XX male syndrome (also called de la Chapelle syndrome, for Albert de la Chapelle, who characterized it in 1972) is a rare congenital condition where an individual with a female genotype has phenotypically male characteristics that can vary between cases. In 90% of these individuals the syndrome is caused by unequal crossing over between X and Y chromosomes during meiosis in the father, which results in the X chromosome containing the normally male SRY gene. When this X combines with a normal X from the mother during fertilization, the result is an XX male. Less common are SRY-negative XX males which can be caused by a mutation in an autosomal or X chromosomal gene or undetected mosaicism with a Y-bearing cell line.

This syndrome is diagnosed through various detection methods and occurs in approximately 1:20 000 newborn males, making it less common than Klinefelter syndrome.

Contents

  [[null hide]] 

• 1Presentation
• 2Genetic Profile
• 3Masculinization
• 4Clinical Diagnosis
• 5Treatment
• 6See Also
• 7References

Presentation[edit]

The appearance of XX males can fall into one of three categories: 1) males that have normal internal and external genitalia, 2) males with external ambiguities, and 3) males that have both internal and external genital ambiguities (true hermaphrodites). Genital ambiguities can include hypospadias, micropenis, and clitormegaly. On average, the appearance of XX males differs from that of an XY male in that they are smaller in height and weight. Most XX males have small testes, are sterile, and have an increase in maldescended testicles compared to XY males. Some XX male individuals have decreased amounts of body hair and decreased libido. Individuals with this condition sometimes have feminine characteristics, with varying degrees of gynecomastia but with no intra-abdominal Müllerian tissue. According to research at the University of Oklahomahealth science centers, despite XX males exhibiting feminine characteristics, their behaviours are usually representative of masculinity in their culture.

Genetic Profile[edit]

Males typically have one X chromosome and one Y chromosome in each diploid cell of their bodies. Females typically have two X chromosomes. XX males that are SRY-positive have two X chromosomes, with one of them containing genetic material from the Y chromosome, making them phenotypically male but genetically female.

SRY-Positive

A translocation between two alleles.

The SRY gene plays an important role in sex determination by initiating testicular development. In most XX males the SRY gene is present. The tip of the Y chromosome contains the SRY gene and, during recombination, a translocation occurs in which the SRY gene on the Y chromosome is moved to become part of an X chromosome. The presence of the translocated SRY gene leads to an XX embryo developing male characteristics.

SRY-Negative

In rare cases, an XX male does not have the SRY gene. The exact cause of this condition is unknown but it has been proposed that mutations in the SOX9 gene may contribute to this syndrome since SOX9 plays a role in testes differentiation during development. Another proposed cause is mutations to the DAX1 gene which encodes a nuclear hormone receptor. DAX1 represses masculinizing genes, therefore, if there is a loss of function of DAX1 then testes can develop in an XX individual. Mutations in SF1 and WNT4 genes are also being studied in connection with SRY-negative XX male syndrome.

Masculinization

The degree to which individuals with XX male syndrome develop the male phenotype is variable, even among SRY-positive individuals. A completely male phenotype develops in the presence of the SRY gene but, in some cases, the presence of the SRY gene can result in internal and/or external genitalia ambiguities. Normal XX females undergo X inactivation during which one copy of the X chromosome is silenced. It is thought that X inactivation in XX males may account for the genitalia ambiguities and incomplete masculinization seen in SRY-positive XX males. The X chromosome with the SRY gene is preferentially chosen to be the active X chromosome 90% of the time, which is why a complete male phenotype is often seen in SRY-positive XX males. In the remaining 10% X inactivation spreads to include a portion of the SRY gene, resulting in incomplete masculinization.

Masculinization of SRY-negative XX males is dependent upon which genes have mutations and at what point in development these mutations occur. The exact causes and mechanisms are currently unknown.

Clinical diagnosis[edit]

In cases where the individual is being evaluated for ambiguous genitalia, such as a small phallus, hypospadias, or labioscrotal folds, exploratory surgery may be used to determine if male and/or female internal genitalia is present.

A standard karyotype can be completed to cytogenetically determine that an individual with a partial or complete male phenotype has a XX genotype.

FISH analysis determines the presence or absence of the SRY gene.

Treatment[edit]

XX males are sterile due to low or no sperm content and there is currently no treatment to address this infertility. Genitalia ambiguities, while not necessary to treat for medical reasons, can be treated through the use of hormonal therapy, surgery, or both. Since XX male syndrome is variable in its presentation, the specifics of treatment varies widely as well. In some cases gonadal surgery can be performed to remove partial or whole female genitalia. This may be followed by plastic and reconstructive surgery to make the individual appear more externally male. Conversely, the individual may wish to become more feminine and feminizing genitoplasty can be performed to make the ambiguous genitalia appear more female. Hormonal therapy may also aid in making an individual appear more male or female.

See also[edit]

• Androgen insensitivity syndrome
• Karyotype
• X chromosome, for other diseases related to the X chromosome.
• XY gonadal dysgenesis (Swyer syndrome)

References[edit]

de la Chapelle, Albert (1985). Cytogenetics of the mammalian X-chromosome, Part B: Progress and topics in cytogenetics. New York: Alan Liss. pp. 75–85.

Week 7 - Ideas for XX Male Syndrome Improvement & Bibliography

Ideas:

• expand on how the two X chromosomes work and explore if duplicate X genes are inactivated
• describe how sexual differentiation occurs with respect to this syndrome
• explain how it effects puberty
• expand on the presentation section to give a more detailed overview
• differentiate between XX male syndrome SRY-positive and SRY-negative
• fix the citations because it is word-for-word from an article
• there are further methods used to detect XX male syndrome to be added

Potential Articles for Bibliography:

Original journal article within this website needs to be found and cited.

OMIM to explore:

Week 5 - Possible Topics

Topic One: Euchromatin

• definition could be expanded
• structure needs additional detail
• it could be compared to heterochromatin
• effects on transcription are bare bones and could be elaborated on
• epigentics could be discussed in relation to euchromatin and heterochromatin
• possible discuss how research uses DNase I to cut euchromatin
• image may not be the best one out there to represent the topic

Topic Two: Trisomy

• more detailed explanation of how trisomy can occur is needed
• there is a lot of repetition that needs cleaned up
• not all trisomies cause problems and those merit discussion too
• there is a debate on "trisomy of sex chromosomes", as stated on the talk page, which could be researched and answered
• it needs a lot of general editing to increase readability
• trisomy detection could be added

Topic Three: XX Male Syndrome

• needs a description of how the two X chromosomes work --is X inactivation happening?
• needs general editing to make it easier to read and to increase clarity
• the "rare" cases need to be expanded on
• further information on presentation needs added
• need to discuss how the SRY gene gets expressed
• it doesn't discuss much research regarding the effects this has an an individual - could be added
• talk page suggests checking for research to see if there is a link between transgendered individuals and XX Male Syndrome

Week 4 - Add to an Article

• proposed an edit with two citations on the "Red Hair" Wikipedia page

Article Evaluation

"Red Hair-Genetics"

• needs citations in first paragraph regarding percentages and frequency
• needs citation for pigment levels
• no citation about portrayal of red-heads
• talks about how they range from admired to ridiculed but gives no details on this
• the discovery of the genetics of red hair is not cited
• discussion about relationship between hair pigment gene and fair skin tone is very poorly worded and difficult to understand
• citation for connection to cancer needed
• talks about genetic relationships (no citation) but not about the mechanisms behind them
• no citation for the gene origin
• discusses mode of inheritance but does not link to a the Wiki page discussing this mode
• no citation for comment about red hair in other species
• the citations I checked are legitimate primary articles from reliable sources
• the article does appear to look at a variety of views on red hair from a neutral perspective
• articles discusses modern common beliefs but references sources that are not necessarily modern. It would be helpful if they added in more current examples of "temperament".
• it could use further detail under the "Genetics" subheading about mode of transmission. It mentions the mode but a breakdown with illustrations of where on chromosome 16 these alleles are found could be useful
• there is very little talk on the talk page. Further sourcing is recommended as well as further information on mythology. Looks like it needs more people interested in the topic to increase the quality of the article.
• overall needs more detailed information, and further citations

Looks great. Keep it up! AdamCF87 (talk) 15:41, 17 October 2017 (UTC)