Late-Onset Rapidly Progressive Spastic Paraplegia with Extensive White Matter Abnormalities Associated with an MFN2 Variant.

Mitofusin-2 (MFN2) variants are a well-established cause of Charcot-Marie-Tooth disease type 2A, although central nervous system involvement has increasingly been recognized in a subset of affected patients. We report a 51-year-old woman carrying a likely pathogenic MFN2 variant (c.2119C>T, p.Arg707Trp) who developed rapidly progressive spastic paraplegia and became wheelchair-dependent within several months. Neurological examination demonstrated severe pyramidal tract signs with preserved sensory function. Nerve conduction studies were suggestive of distal motor axonal involvement, while transcranial magnetic stimulation and somatosensory evoked potentials indicated corticospinal and central sensory pathway dysfunction in the lower extremities. Brain magnetic resonance imaging revealed extensive bilateral confluent periventricular and deep white matter hyperintensities. Comprehensive investigations excluded inflammatory, vascular, metabolic, infectious, neoplastic, and common genetic causes of hereditary spastic paraplegia. Targeted next-generation sequencing identified a heterozygous likely pathogenic MFN2 p.Arg707Trp variant. Although central nervous system manifestations have previously been described in MFN2-related disease, this phenotype is unusual because of the combination of late-onset rapidly progressive spastic paraplegia, and extensive cerebral white matter abnormalities associated with the p.Arg707Trp variant. This case further expands the recognized phenotypic spectrum of MFN2-related disease and highlights that MFN2 variants should be considered in the differential diagnosis of selected patients with late-onset progressive spastic paraplegia accompanied by cerebral white matter abnormalities and distal motor axonal neuropathy.