Extreme Phenotypic Variability of ACTG1‐Related Disorders in Hearing Loss

Hearing loss is the most common sensory defect in humans, affecting normal communication. In most cases, hearing loss is a multifactorial disorder caused by both genetic and environmental factors, but single‐gene mutations can lead to syndromic or non‐syndromic hearing loss. Monoallelic variants in ACTG1, coding for gamma (γ)‐actin, are associated with classical Baraitser‐Winter Syndrome type 2 (BRWS2, nonsyndromic deafness, and a variety of clinical presentations not fitting the original BRWS2 description or nonsyndromic deafness. Here two unrelated patients with ACTG1 variants are reported, having severe hearing loss as a common phenotype but with different clinical presentations, supporting the extreme variability of ACTG1‐related disorders. Different variants in a single gene can confer genetic pleiotropy (different phenotypes). One example is monoallelic variants in the ACTG1, coding for gamma (γ)‐actin, which is associated with classical Baraitser‐Winter Syndrome type 2 (BRWS2) and a variety of clinical presentations not fitting the original BRWS2 description including non‐syndromic deafness. Here two unrelated patients with ACTG1 variants are reported, having severe hearing loss as a common phenotype but with different clinical presentations, supporting the extreme variability of ACTG1‐related disorders.