Which syndrome is specifically associated with a deletion on chromosome 22?

• A. Turner syndrome
• B. DiGeorge syndrome
• C. Klinefelter syndrome
• D. Marfan syndrome

Answer: (B)

A deletion on chromosome 22, specifically the 22q11.2 region, leads to DiGeorge syndrome. This microdeletion disrupts the development of several structures derived from the pharyngeal arches, resulting in thymic and parathyroid hypoplasia (immune deficiency and hypocalcemia), congenital heart defects, and palate abnormalities. It’s also known as velocardiofacial syndrome.

The other conditions involve different chromosomal changes or gene mutations: Turner syndrome results from monosomy X; Klinefelter syndrome from an extra X chromosome in males (XXY); Marfan syndrome comes from mutations in the FBN1 gene, not a chromosome 22 deletion. Thus, the chromosome 22 deletion most specifically points to DiGeorge syndrome.