Atypical features including acquired oculomotor apraxia in C9orf72-associated familial primary lateral sclerosis

The phenotypic variability of C9orf72-associated disease is broadening, including atypical and non-motor presentations. C9orf72-associated neurodegeneration has only rarely been associated with primary lateral sclerosis (PLS), and even more rarely with ocular motor apraxia.

Describe a family with C9orf72 mutation presenting with frontotemporal dementia (FTD) and atypical PLS phenotypes and discuss the implications regarding 1) where PLS lies on the ALS-FTD spectrum, and 2) how C9orf72 mutations influence PLS clinically.

Chart review.

A 52-year-old male experiencing 4 months of progressive right lower leg spasticity with a family history of FTD was referred to us. Within 15 months, he was anarthric and required a powered wheelchair. He developed acquired ocular motor apraxia, consistent with supranuclear ophthalmoplegia. He later developed laryngeal dystonia which led to his death. Ten years later, his 67-year-old brother presented with 8 months of progressive spastic dysarthria, hyperreflexia, right foot drop, and right facial weakness. Genetic testing revealed heterozygous C9orf72 hexanucleotide repeat expansion.

This family's presentation expands on sparse reports of C9orf72-associated PLS. The proband showcases a severity of ocular motor deficits not yet reported in PLS, extending ocular motor findings in MND. These deficits also provide clinical evidence of degeneration outside the motor cortex/spinal cord in PLS. The symptomatology (laryngeal dystonia, rapid progression) clinically overlaps with ALS/FTD, suggesting PLS may lie on the ALS-FTD spectrum. The severity and atypicality of this case also support suggestions that C9orf72 mutations amplify the spectrum/severity of disease observed in TDP-43 proteinopathies.