Swyer syndrome

Swyer syndrome

: A person is born without functional gonads and known as XY gonadal dysgenesis.

:is a condition in which individuals with one X chromosome and one Y chromosome in each cell, the pattern normally found in males, have a female appearance. 

People with this disorder have female external genitalia and a normal uterus and Fallopian tubes. However, they do not have functional gonads (ovaries or testes). 

Their gonads are minimally developed clumps of tissue present instead testes or ovaries.

This kind of gonad in swyer syndrome are known as gonadal streaks. These abnormal gonads often become cancerous, so they are usually removed surgically early in life.

Causes:

1)    Mutations in the SRY gene (15 % to 20 %): prevent production of the sex-determining region Y protein or result in the production of a nonfunctioning protein. This fetus will develop as a female despite having a Y chromosome.

2)     Mutations in the NR5A1 and DHH genes (small number): The NR5A1 gene produce transcription factor steroidogenic factor 1 that help to produce sex hormones and development of male sexual characteristics. The DHH gene produce a member of the hedgehog protein family. Hedgehog proteins are important for early development in many parts of the body. Mutations in the NR5A1 and DHH genes impair the process of male sexual differentiation, causing to develop a female appearance despite having a Y chromosome.

3)     Changing in the NR0B1 gene (small number): The NR0B1 gene provides a DAX1 protein that have important role in the development and function of gonads. A duplication of a region in the X chromosome can result in an extra copy of the NR0B1 gene, which leads to the production of extra DAX1 protein. Before birth, an excess of DAX1 protein prevents the formation of male reproductive tissues, including the testes and male external genitalia.

These people are typically raised as females and have a female gender identity.

Treatment: hormone replacement therapy during adolescence to induce menstruation and development of female secondary sex characteristics such as breast enlargement and body hair.

http://www.webmd.com/a-to-z-guides/swyer-syndrome

http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/1204/viewAbstract

Leydig cell hypoplasia

Leydig cell hypoplasia

: a rare autosomal  recessive genetic and endocrine syndrome that affects male sexual development. 

characterized by: underdevelopment (hypoplasia) of Leydig cells in the testes.

Leydig cells function: secrete androgen that are important for normal male sexual development before birth and during puberty.

Affected person:  typical male chromosomal pattern (46,XY), 

have a small penis (micropenis), the opening of the urethra on the underside of the penis (hypospadias), and a scrotum divided into two lobes (bifid scrotum), ambiguous genitalia.

They do not develop secondary sex characteristics, such as increased body hair, at puberty.

Mutations in the LHCGR gene cause Leydig cell hypoplasia.

 The LHCGR gene provides the luteinizing hormone/chorionic gonadotropin receptor.

 In males: chorionic gonadotropin stimulates the development of Leydig cells in the testes and LH cause produce androgens like testosterone  that control male sexual development and reproduction. 

In females: LH triggers the release of egg cells from the ovary (ovulation). Chorionic gonadotropin is produced during pregnancy and helps maintain conditions necessary for the pregnancy to continue.

Leydig cell hypoplasia:  disrupt LH/chorionic gonadotropin receptor function.

In males:  poorly developed or absent Leydig cells and impaired production of testosterone. 

A lack of testosterone: poorly development of male sexual organs before birth.

http://onlinelibrary.wiley.com/doi/10.1046/j.1464-410X.1998.00503.x/pdf

http://press.endocrine.org/doi/pdf/10.1210/jc.2004-0298

http://link.springer.com/chapter/10.1007/978-1-4419-8002-1_32

DOWN SYNDROME

DOWN SYNDROME

:is a chromosomal condition caused when abnormal cell division results in extra genetic material from chromosome 21.

 

causes intellectual disability (developmental delays), Flattened facial features, Protruding tongue, small stature, an upward slant to the eyes, single deep crease across the center of the palm and weak muscle tone in infancy.

One in every 691 babies in the United States is born with Down syndrome. Approximately 400,000 Americans have Down syndrome and about 6,000 babies with Down syndrome are born in the United States each year.

There are three types of Down syndrome:  trisomy 21 (nondisjunction), translocation and mosaicism.                             

About 95% of cases Down syndrome are usually caused by nondisjunction that is called trisomy 21.   Nondisjunction results in abnormal cell division during the development of the sperm cell or the egg cell with three copies of chromosome 21 instead of the usual two. 

Mosaicism occurs when nondisjunction of chromosome 21 takes place in one but not all cells. It is caused by abnormal cell division after fertilization. Children have some cells with an extra copy of chromosome 21.  Mosaicism is rare and accounts for about 1% of all cases of Down syndrome.

About 4% of all cases of Down syndrome are translocation.  In translocation, part of chromosome 21 becomes attaches to another chromosome, typically chromosome 14.  These children have the usual two copies of chromosome 21 and total number of chromosomes in the cells remains 46 but an extra part of chromosome 21 causes the characteristics of Down syndrome. 

Risk factors: advancing maternal age, having had one child with Down syndrome, and being carriers of the genetic translocation for Down syndrome.

I have one cousin that has Down Syndrome because of  his mother maternal age. I think that this kind of children needs really good educational support. My cousin knew the capital city of most of the countries in the world at age 4. His mom and sister really support him and speak with him all the time. it is really good for them to have as much as communication with people. they can not grow up like other children but at least they can be good in their ways. 

http://geneticdisordersp7.wikispaces.com/Down+Syndrome

http://comd281-summerwiki.wikispaces.com/Group+5++Down+Syndrome

http://www.chw.org/medical-care/genetics-and-genomics-program/medical-genetics/chromosome-abnormalities/types-of-chromosome-abnormalities/structural-abnormalities/translocations/

http://ghr.nlm.nih.gov/condition/down-syndrome

PENTA X SYNDROME

PENTA X SYNDROME

• 49, XXXXX Chromosome Constitution
• 49, XXXXX Karyotype
• 49,XXXXX Syndrome
• Pentasomy X
• XXXXX Syndrome

penta X Syndrome is a rare chromosomal disorder that affects females.

In Penta X Syndrome, there are three additional (or a total of five) X chromosomes in the nuclei of body cells (pentasomy X).

The condition is typically characterized by:

 Moderate to severe mental retardation, short stature, malformations of the skull and facial region, and other physical abnormalities.Characteristic craniofacial malformations may include upslanting eyelid folds, a flat nasal bridge, malformed ears, a short neck with a low hairline.

Penta X Syndrome is characteristically associated with growth delays before birth.

Females with Penta X Syndrome have 49 chromosomes, five of which are X chromosomes. The presence of the three additional X chromosomes results from errors during the division of reproductive cells in one of the parents (nondisjunction during meiosis).

 Evidence suggests that the extra X chromosomes are typically derived from the mother.

 Researchers indicate that the risk of such errors may increase with advanced parental age.

http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/790/viewFullReport

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