Which inheritance pattern best describes X-linked SCID?

Which inheritance pattern best describes X-linked SCID?

• A. Autosomal dominant
• B. X-linked dominant
• C. X-linked recessive
• D. Autosomal recessive

Answer: (C)

X-linked recessive inheritance is at play here. The gene involved sits on the X chromosome, and a single mutated copy on the X is enough to cause disease in males, who have only one X. Females have two X chromosomes, so a single mutated copy usually doesn’t produce symptoms and instead makes them carriers. In X-linked SCID, most affected individuals are males, because they inherit the mutated X from a carrier mother and have no second X to compensate. Those males pass the mutated X to all daughters (who become carriers) and none to their sons (they pass a Y to sons). This pattern—predominantly affected males with carrier females and no male-to-male transmission—best fits X-linked recessive.

X-linked recessive inheritance is at play here. The gene involved sits on the X chromosome, and a single mutated copy on the X is enough to cause disease in males, who have only one X. Females have two X chromosomes, so a single mutated copy usually doesn’t produce symptoms and instead makes them carriers. In X-linked SCID, most affected individuals are males, because they inherit the mutated X from a carrier mother and have no second X to compensate. Those males pass the mutated X to all daughters (who become carriers) and none to their sons (they pass a Y to sons). This pattern—predominantly affected males with carrier females and no male-to-male transmission—best fits X-linked recessive.