Novel Splice-Site Variant Causing Distal Motor Neuropathy and Occipital Horn Syndrome: Two Siblings and Literature Review.

Pathogenic hemizygous variants in most commonly cause Menkes disease or occipital horn syndrome (OHS), whereas -related distal hereditary motor neuropathy (dHMN) is rarely reported. Here, we describe two adult brothers with an overlapping dHMN/OHS phenotype caused by a novel splice-site variant and review the clinical and genetic features of previously published patients with -related dHMN. We performed detailed clinical, electrophysiological, and genetic evaluations of both siblings, including exome sequencing and RNA analysis. Additionally, we reviewed the clinical, electrophysiological, and genetic data of previously reported patients with -related dHMN. We identified a novel hemizygous splice-site variant (NM_000052.7:c.1544-2A>T) in both brothers. The younger brother, who exhibited a more severe phenotype, presented in early childhood with mild global developmental delay, intellectual disability, and chronic diarrhea, while the older brother had childhood-onset chronic diarrhea without cognitive impairment. Both developed distal hereditary motor neuropathy later in life, and imaging revealed occipital horns. Serum copper and ceruloplasmin levels were mildly reduced. RNA sequencing revealed two aberrant transcript isoforms resulting from the splice-site variant, one of which may produce a partially functional protein. Review of previously reported patients shows that -related dHMN may occur isolated or with overlapping features of OHS. In patients with the overlapping phenotype, chronic diarrhea was often the first symptom, followed by slowly progressive dHMN. Previously reported -related dHMN has been mostly associated with missense variants. Our findings expand the mutational spectrum by identifying a splice-site variant. In patients with an overlapping OHS/dHMN phenotype, diagnosis was typically delayed for decades, suggesting this presentation remains underdiagnosed.