Alport Carrier Pregnancy 50 Percent Sons Risk — ESENeph MCQ

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ModeratePregnancy & RenalAlport Carrier Pregnancy 50 Percent Sons RiskESENeph

A 28-year-old woman at 16 weeks' gestation has known Alport syndrome (COL4A5 carrier) with eGFR 65 mL/min/1.73m2 and uPCR 80 mg/mmol. She was on ramipril pre-pregnancy (now stopped). Her BP is 130/82 mmHg on labetalol. She asks about outcomes for the fetus. Given her X-linked Alport carrier status, what proportion of her male offspring will be affected by Alport syndrome?

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Correct answer: C — 50%

In X-linked Alport syndrome, a heterozygous carrier mother has one normal X chromosome and one carrying the COL4A5 mutation. Each son receives his sole X chromosome from the mother — there is a 50% chance of receiving the affected X. Males who inherit the mutation are hemizygous and will develop the full Alport phenotype (progressive CKD, hearing loss). Daughters have a 50% chance of being carriers (heterozygous), with variable expression. This counselling is important for reproductive planning. Prenatal genetic testing is available if the family mutation is known. The mother herself, as a carrier, may have variable severity ranging from benign haematuria to progressive CKD — her eGFR 65 with proteinuria indicates moderate disease.

Reference: Kashtan 2021 – Alport Syndrome; JRCPTB 2022 – Nephrology Curriculum