1. Turner syndrome: (X instead of XX or XY). In Turner syndrome, female sexual characteristics are present but underdeveloped. People with Turner syndrome often have a short stature, low hairline, abnormal eye features and bone development and a “caved-in” appearance to the chest. Description: Turner syndrome (TS) occurs when one of the two X chromosomes in females is either missing or incomplete. The most common symptoms are short stature and gonadal dysgenesis, which can cause incomplete sexual development and ovarian failure and infertility.
As of right now, there is no known cause of TS. 2. Klinefelter’s syndrome (XXY): Description Men with Klinefelter syndrome are usually sterile, and tend to have longer arms and legs and to be taller than their peers. Boys with the syndrome are often shy and quiet, and have a higher incidence of speech delay and dyslexia. During puberty, without testosterone treatment, some of them may develop gynecomastia. 3. Patau Syndrome: also called D-Syndrome or trisomy-13.
Symptoms are somewhat similar to those of trisomy-18, but they do not have the characteristic hand shape Description: Trisomy 13, also called Patau syndrome, is a disorder in which an individual has three copies of genetic material from chromosome 13, rather than two. It can occur in three forms: Trisomy 13, which has a third chromosome 13 in all cells; Trisomy 13 mosaicism, which has a third chromosome 13 in some cells; and partial Trisomy, which has the presence of part of an extra chromosome 13 in the cells.
4. Down syndrome: Description usually is caused by an extra copy of chromosome 21 (trisomy 21). Characteristics include decreased muscle tone, stockier build, asymmetrical skull, slanting eyes and mild to moderate mental retardation. 5. Edwards syndrome: Description which is the second-most-common trisomy; Down syndrome is the most common. It is a trisomy of chromosome 18. Symptoms include mental and motor retardation and numerous congenital anomalies causing serious health problems. Ninety percent die in infancy; however, those that live past their first birthday usually are quite healthy thereafter.
Some symptoms include clenched hands, feet with a rounded bottom, mental deficiency, underdeveloped fingernails, and an unusual shaped chest. 6. Cat eye syndrome: Description: For individuals with cat eye syndrome, the short arm (known as 22p) and a small region of the long arm (22q) of chromosome 22 are present three or four times, rather than twice. Characteristic features of the disorder include mild growth delays before birth, mild mental deficiency, and malformations of the skill and facial region, the heart, the kidneys, and/or the anal region.
7. Williams Syndrome: Description: Williams syndrome is caused by a deletion of genetic material from portions of the long arm of chromosome 7, a region that consists of more than 25 genes. Researchers have identified a few of the specific genes related to Williams syndrome, but the relationship between most of the genes in the deleted region and the symptoms of Williams syndrome is still unknown. The most common symptoms of Williams syndrome are mental retardation, heart defects, and unusual facial features ,small upturned nose, wide mouth, full lips, small chin, widely spaced teeth . Angelman syndrome: Description: Angelman syndrome (AS) is an example of genomic imprinting, where the deletion or inactivation of genes on the maternally inherited chromosome 15 causes the paternal copy, which may be of normal sequence, to be imprinted and silenced. AS is characterized by intellectual and developmental delays, sleep disturbances, seizures, and jerky movements, but also frequent laughter or smiling and usually have a happy demeanor