Multiple system atrophy and amyotrophic lateral sclerosis in a family with hexanucleotide repeat expansions in C9orf72.

IMPORTANCE: Here we report a family with coexistence of multiple system atrophy (MSA) and amyotrophic lateral sclerosis (ALS) with hexanucleotide repeat expansions in C9orf72. OBSERVATIONS: A 65-year-old woman had a 2-year history of ataxia with autonomic dysfunction but without motor neuron signs. She was diagnosed as having MSA based on her clinical history and the hot cross bun sign on brain magnetic resonance imaging. Her 62-year-old brother had progressive weakness, fasciculations, hyperreflexia, and active denervation on electromyography without cerebellar ataxia. He was diagnosed as having ALS. Both patients had a greater than 1000/2 hexanucleotide expansion in C9orf72. CONCLUSIONS AND RELEVANCE: Patients with hexanucleotide repeat expansions in C9orf72 can present with MSA as well as ALS or frontotemporal dementia. We report this family with coexisting MSA and ALS, highlighting the phenotypic variability in neurologic presentations with hexanucleotide repeat expansions in C9orf72.