Chromosome 21, tetrasomy 21q

Chromosome 21, tetrasomy 21q is a rare chromosomal abnormality in which an individual has an extra copy of the long arm (q arm) of chromosome 21. This condition is a type of tetrasomy, which refers to the presence of four copies of a particular chromosome or part of a chromosome, instead of the normal two. The specific segment involved in this condition is the long arm of chromosome 21, designated as 21q. The presence of an extra genetic material from chromosome 21 can lead to various developmental and medical challenges.

Causes

Tetrasomy 21q is caused by a random error in cell division, either during the formation of reproductive cells (gametes) or in early fetal development. The error can occur in two main ways: through a process called nondisjunction, where chromosomes do not separate properly during cell division; or through an aneuploidy event, where an individual has an abnormal number of chromosomes. In the case of tetrasomy 21q, the result is an extra copy of the long arm of chromosome 21.

Symptoms and Diagnosis

The symptoms of tetrasomy 21q can vary widely among affected individuals but may include intellectual disability, developmental delays, congenital heart defects, distinctive facial features, and other physical abnormalities. The severity of symptoms can depend on the extent of the duplication and the specific genes involved.

Diagnosis of tetrasomy 21q typically involves genetic testing, including karyotyping and fluorescence in situ hybridization (FISH), to identify the chromosomal abnormality. Prenatal testing may also detect the condition in some cases.

Treatment and Management

There is no cure for tetrasomy 21q, and treatment focuses on managing symptoms and supporting the individual's development. This may include early intervention services, special education programs, and therapies such as speech, occupational, and physical therapy. Medical management may be necessary for associated health issues, such as heart defects or other congenital anomalies.

Prognosis

The prognosis for individuals with tetrasomy 21q varies depending on the severity of symptoms and associated health conditions. With appropriate support and treatment, many individuals with this condition can lead fulfilling lives.

See Also

• Chromosome 21
• Genetic disorder
• Chromosomal abnormalities
• Intellectual disability