A Brief Overview of Sexual Chromosome Disorders

A Brief Overview of Sexual Chromosome Disorders

Klinefelter syndrome (47. XXY)

It occurs in 1 in 1,000 boys.

 These children have learning difficulties, especially verbal skills.

 Adults have long stature, gynecomastia (breast enlargement), leg ulcers, osteoporosis, and breast carcinoma, which are secondary to testosterone treatment and prevent osteoporosis. These people are usually infertile due to the lack of sperm in the semen (azoospermia).

The origin of the extra chromosome is almost equal to that of the parent. ”The extra maternal X chromosome is due to the mother's advanced age.

 A small proportion of cases are in the form of mosaicism (47, XXY / 46, XY).

 Rarely is a man with more than two X chromosomes (48, XXXY) or (49, XXXXY) because they are very retarded and have more severe physical symptoms than Klein-Felter patients.


Turner syndrome (45, X):

It occurs in 1 in 5,000 to 10,000 baby girls.

 Turner syndrome is detected in the second trimester by ultrasound, which is characterized by a person (hydrops) or swelling of the neck (posterior neck cyst) or an increase in the thickness of the back of the neck.

In this syndrome, intrauterine edema, scaly neck, short fourth meta-carp bone (between the wrist and fingers), distal nipples, and aortic stenosis are seen.

 Their intelligence is natural and the differences in their social understanding are at the origin of the X chromosome. They have a short stature due to the failure of the SHOX haplogen in the false autosomal recessive region.

Defective ovaries lead to a lack of menstruation and infertility. Estrogen therapy creates secondary sexual characteristics and prevents osteoporosis.

In 80% of cases, Turner's syndrome is caused by the loss of the X or Y chromosome in paternal meiosis.

Cases of cellular mosaicism (46, XX) can be fertilized, but cases of mosaicism with (46, XY) degeneration of gonads.


Women XXX:

0.1% of births have karyotypes 47, XXX.

In 95% of cases, the human X chromosome is of maternal origin and is caused by meiosis I error.

These people have a natural appearance, are fertile and do not have much intelligence skills.

Women with two or more extra X chromosomes have learning difficulties.


XYY Men:

It occurs in 1 in 1,000 boys.

Excess Y is due to non-separation of paternal meiosis II or mitotic divisions after egg formation.

They have normal faces and are fertile, and their IQ is slightly lower than normal.


Fragile X Syndrome:

It occurs in 1 in 5,000 boys and is responsible for 8-4% of learning problems in men.

The most common inherited cause is learning disabilities and is the first known patient with dynamic mutations.

 Another name for it is Martin-Bell syndrome. Their faces are prominent. "They have prominent foreheads, large ears, long faces and prominent jaws.

 After the maturation of the large testicle (macro-orchidism), there is a weakness of the connective tissue of the joint with high traction, the presence of lines and grooves on the skin, and the prolapse of the mitral valve.

Learning problems range from moderate to severe, stuttering, hyperactivity, and daydreaming. 50% of women with a complete mutation have learning difficulties.

The syndrome is named because of a fragile position near the telomere at the end of the long arm of the chromosome (Xq27.3), which is usually a colorless fissure.

 In culture conditions such as folate and thymidine removal, fragile sites can be identified in more than 50% of cells, but molecular methods are also needed for accurate identification.

Healthy individuals on the 5UTR FMR-1 gene in the FRAXA leukemia have about 10-50 repetitions of three CGG nucleotides that are consistently inherited.

If the number of repetitions is between 59 and 200 (pre-mutations), they are prone to instability. Repetitions are 51 to 58 in the middle.

People with pre-mutations have a normal state, although there is a possibility of fragile X-ray syndrome / ataxia in adults.

 If the repetitions extend to more than 200 repetitions (full mutation), they become unstable during transmission from the female meiosis and during mitotic divisions (dynamic or dynamic mutations).

Natural and mutant alleles are identified by PCR, while saturn bluetooth should be used to detect complete mutations.

In complete mutations, hypermethylation occurs and the FMR-1 gene transcription is suppressed.

 The FMR gene has 17 exons and encodes a cytoplasmic protein that plays an essential role in the development and function of brain neurons.

In the Xq28 area, there is another fragile area with a milder clinical sign called FRAXE, which consists of a repetitive sequence of three CGGs and its frequency is 1: 4, FRAXA.

 The other area is FRAXA, which is not associated with clinical abnormalities.