Which chromosomal microdeletion is associated with DiGeorge syndrome?

• A. 7q11 microdeletion
• B. 18p deletion
• C. 22q11 microdeletion
• D. 15q deletion

Answer: (C)

DiGeorge syndrome is caused by a microdeletion on chromosome 22 at the q11.2 region. Losing this piece of DNA disrupts the development of the third and fourth pharyngeal pouches, leading to thymic hypoplasia or aplasia, parathyroid hypoplasia, and common heart defects that involve the connecting outflow tract. The TBX1 gene in this region is a key player; its reduced dosage disrupts neural crest cell migration and pharyngeal arch development, producing the characteristic combination of immune deficiency, calcium problems, and heart and facial anomalies. That specific 22q11.2 deletion is the classic link to DiGeorge syndrome. Other listed deletions correspond to different syndromes (for example, 7q11.23 with Williams syndrome, and deletions on 18p or 15q associated with other conditions) and do not produce the same DiGeorge features.