Biallelic

Both copies of a gene affected

Biallelic means both copies (alleles) of a gene are affected. In recessive disease, both copies must carry a pathogenic variant for disease to appear, while a single working copy is usually enough for normal function. When both copies are non-functional, the term biallelic null is used. Many recessive CMT subtypes are biallelic, whether homozygous (the same variant on both copies) or compound heterozygous (a different variant on each).

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