Jacob syndrome, also known as 47, XYY syndrome, is a rare disorder that affects the male population. Normally, a male inherits an X and a Y chromosome from the parents. Individuals with this syndrome have an extra copy of the Y chromosome and usually appear to be very tall. Most of the affected individuals do not have unusual physical features and continue to have normal sexual development. This syndrome is estimated to affect around 1 in 1,000 newborn boys.
Causes
Two of the 46 chromosomes are called the sex chromosomes as they determine the sexual characteristic of the individual. Females have two X chromosomes (46, XX) and males have one X chromosome and one Y chromosome (46, XY). Jacob’s syndrome is characterized by the presence of an extra Y chromosome in each of the cells. Some of the individuals only have one extra Y chromosome in some of their cells which is known as 46,XY/47,XYY mosaicism. It is not completely clear how the extra copy of the Y chromosome is related to the features of this condition. Most of the cases of Jacob syndrome are not inherited, meaning it occurs as a random change during the development of the sperm cells. This is caused by the error in cell division known as nondisjunction that results in the extra Y chromosome.
Symptoms
The most common feature of this condition is the increased height that is evident around the age of 6 resulting in an average adult height of 6 feet and 3 inches. Generally, these cases don’t have a problem with the sexual development continuing to have normal fertility. The intelligence appears to be unaffected with some developing severe cystic acne during adolescence. Affected boys can exhibit mild developmental delays, learning disabilities such as speech delays and reading difficulties associated with dyslexia. They are also at increased risk of autism spectrum disorder, attention deficit and hyper-activity disorder.
Diagnosis
The diagnosis is based on the clinical evaluation, history of the individual and various tests. However, most of the cases often remain undiagnosed until adulthood. When this condition is suspected, the chromosome analysis can identify the presence of an extra chromosome. Prenatal diagnosis is possible through amniocentesis or chorionic villus sampling (CVS). During the amniocentesis, the fluid around the fetus is removed and analyzed while the CVS procedure involves the removal of the tissue sample from the placenta.
Treatment
The treatment for this condition is symptomatic and supportive. In most of the cases, the early intervention is highly beneficial to resolve the problem within a few years. In addition, the occupational or speech therapy may also be beneficial for some of the affected cases. Additional problems such as attention deficit, hyperactivity disorder or behavioral problems should be treated with medication or therapy.
References
https://rarediseases.org/rare-diseases/xyy-syndrome/
https://ghr.nlm.nih.gov/condition/47xyy-syndrome#inheritance