The absence of curly hair is associated with a milder phenotype in Giant Axonal Neuropathy

Giant Axonal Neuropathy is a pediatric neurodegenerative disorder caused by autosomal recessive mutations in the GAN gene on chromosome 16q24.1. Mutations in the GAN gene lead to functional impairment of the cytoskeletal protein gigaxonin and a generalized disorder of intermediate filaments, including neurofilaments in axons. Tightly curled hair is a common but not universal feature of Giant Axonal Neuropathy. The pathogenesis of curly hair is unknown, although disruption of keratin architecture is thought to play a role. As part of a broader natural history study of Giant Axonal Neuropathy, we found that the absence of curly hair is correlated with superior motor function (p = 0.013) when controlling for age, as measured by the Gross Motor Function Measure. Theoretically, higher levels of functional gigaxonin protein or compensatory mechanisms could produce fewer abnormalities of neurofilaments and keratin, accounting for this phenotype. We suggest that straight-haired patients with Giant Axonal Neuropathy are potentially underdiagnosed due to their divergence from the classic phenotype of the disease. Due to their non-specific features of an axonal neuropathy, these patients may be misdiagnosed with Charcot-Marie-Tooth Disease type 2. Genetic testing for Giant Axonal Neuropathy should be considered in relevant cases of Charcot-Marie-Tooth Disease type 2.