USMLE 1 Question 19

A growing number of human diseases have been discovered to be caused by inherited mutations in genes encoding channels.

What inherited ion-channel diseases affects the chloride channel?

a) Liddle's syndrome
b) cystic fibrosis
c) hemoglobin M disease
d) Becker's muscular dystrophy
e) X-linked hereditary nephritis








ANSWER
The correct answer is B



Explanation
The gene responsible for Cystic fibrosis encodes a membrane-associated protein called the cystic fibrosis transmembrane regulator.

The most common gene mutation, F508, leads to absence of a phenylalanine residue at position 508 on the CFTR protein which is a part of a cAMP-regulated Cl channel and appears to regulate Cl and Na transport across epithelial membranes.

Heterozygotes may show subtle abnormalities of epithelial transport but are clinically normal.

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