Chromosome 22, trisomy

Chromosome 22, trisomy, also known as Trisomy 22, is a rare chromosomal disorder where an individual has three copies of chromosome 22 instead of the usual two. This condition can lead to various developmental and health issues, depending on the extent and nature of the trisomy (full, mosaic, or partial). Trisomy 22 is often associated with miscarriage and is rarely found in live births due to its severe effects.

Causes

Trisomy 22 occurs due to a nondisjunction event during the formation of reproductive cells in a parent or at an early stage of fetal development. Nondisjunction is the failure of chromosomes to separate properly during cell division, resulting in an extra copy of chromosome 22 in the embryo.

Types

There are three main types of Trisomy 22:

• Full Trisomy 22: All cells contain an extra copy of chromosome 22. This form is extremely rare in live births and is usually incompatible with life.
• Mosaic Trisomy 22: Only some of the cells have an extra chromosome 22. The symptoms and severity can vary widely depending on the proportion and distribution of affected cells.
• Partial Trisomy 22: Only a segment of the extra chromosome 22 is present in the cells. The effects depend on which genes are duplicated.

Symptoms

The symptoms of Trisomy 22 can vary significantly but may include:

• Developmental delays
• Intellectual disability
• Congenital heart defects
• Kidney problems
• Facial dysmorphisms such as a small jaw, ear abnormalities, and a cleft palate
• Growth retardation

Diagnosis

Diagnosis of Trisomy 22 can be made through prenatal testing methods such as amniocentesis or chorionic villus sampling (CVS), which analyze the chromosomes in fetal cells. After birth, a blood test called a karyotype can be used to confirm the diagnosis by examining the number and structure of the chromosomes.

Treatment

There is no cure for Trisomy 22, and treatment focuses on managing the symptoms and improving the quality of life for those affected. This may include surgical interventions for physical abnormalities, therapies for developmental delays, and regular monitoring for any health issues associated with the condition.

Prognosis

The prognosis for individuals with Trisomy 22 varies widely depending on the type and severity of the condition. Full Trisomy 22 is typically lethal before birth. Those with mosaic or partial Trisomy 22 may have a range of outcomes, from relatively mild to severe physical and intellectual disabilities.