27th February 2024

X-linked recessive

X-linked recessive conditions are more commonly seen in males, with females often acting as carriers for the gene mutations. Males cannot pass on the mutation to their male children, but females will always act as carriers. A pedigree can show affected males in the generation above the index case. Female carriers will have a 50% chance of bearing a male affected by the condition or a female acting as a carrier for the condition.

Females can occasionally display the diseases’ phenotype through skewed X-inactivation ( X-inactivation favouring the expression of the mutant allele) or if they are homozygous for the mutant allele. Variable expressivity secondary to mosaicism, variable penetrance, and de novo mutations within X-linked mutations can result in an atypical pedigree, preventing the visualisation of a clear inheritance pattern.

Image Source: Wikimedia Commons (2013). Sex linked inheritance, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Sex_linked_inheritance.png (Accessed: 5 January 2024).