Non-clinical sciences/Genetics · Inheritance

Autosomal recessive

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What it means

Two mutant alleles needed; carriers asymptomatic; 25% of offspring of two carriers affected; often skips generations; consanguinity raises risk. Examples: cystic fibrosis, sickle cell, β-thalassaemia, haemochromatosis, Wilson, α1-antitrypsin deficiency, PKU, Friedreich ataxia, congenital adrenal hyperplasia.

Worked example

Two unaffected parents (carriers), an affected child, and consanguinity → autosomal recessive.

In the exam

Two healthy parents — who are cousins — have an affected child, and the condition had not appeared in earlier generations.

What settles it

AR skips generations (carrier parents); AD appears in every generation. Friedreich ataxia is AR despite being a triplet-repeat disease.

Classically confused with

Autosomal dominant

Source: StatPearls