Question

Which of the following results in the congenital defect of the thymus in humans?

• A. Down's syndrome
• B. Cystic fibrosis
• C. DiGeorge syndrome
• D. Fragile X syndrome

Answer 1

The correct option is C DiGeorge syndrome

DiGeorge syndrome results in the congenital (present at birth) defect of the thymus in humans. This disability occurs when a small piece of chromosome number 22 is found (22q11) deleted. Symptoms include several abnormalities, like heart defects, characteristic facial features, breathing problems, underdevelopment or absence of parathyroid and thymus gland.

Figure : DiGeorge syndrome

When the thymus fails to develop, it results in the total absence of T-lymphocytes because thymus is required for the maturation and selection of T-lymphocytes. This affects the cell-mediated immunity.

Down's syndrome resulted due to the trisomy (3 copies) of chromosome number 21. Symptoms include distinct facial appearance, intellectual disability, and developmental delays.

Figure : Down's syndrome

Cystic fibrosis is a condition caused by mutations in cystic fibrosis transmembrane conductance regulator (CFTR) gene. Mucus gets thick and blocks the tracts because of the absence of a chloride channel in this disorder.

Figure : Cystic fibrosis

Fragile X syndrome is a disease caused due to changes in the FMR1 gene. This gene makes a protein called FMRP which is needed for brain development. Symptoms include developmental delays, learning disabilities, social and behavioural problems like anxiety, speaking without thinking, and being hyperactive.

Figure : Fragile X syndrome