Question

All of the following statements about the genetics of G6PD deficiency are true, EXCEPT:

• A. X-linked inheritance
• B. More severe in men
• C. Contradicts the Lyon hypothesis
• D. May affect heterozygous females

Hint:

Variable enzyme levels in carrier females actually prove, not disprove, random X-inactivation.

Answer 1

The Correct Option is C

Step 1: The G6PD gene is located on the X chromosome (Xq28), so the disorder shows X-linked recessive inheritance (option a true). Males have a single X chromosome, so a variant gene is fully expressed and the disease is more severe in men (option b true).

Step 2: According to the Lyon hypothesis, one of the two X chromosomes in each cell of a female is randomly inactivated. A heterozygous female therefore has two red-cell populations, one normal and one G6PD deficient. Depending on the degree of lyonization, she may show normal, moderately reduced, or grossly deficient enzyme activity. Thus heterozygous females CAN be affected (option d true).

Step 3: This mosaic pattern in heterozygous females is exactly what the Lyon hypothesis predicts. G6PD deficiency therefore SUPPORTS the Lyon hypothesis, it does not contradict it.

Step 4: The false statement, and hence the answer, is option c.