TUBA4A Pathogenic Variant Manifesting With Adulthood-Onset Genetic Myasthenic Syndrome, Myopathy, and Infertility.

OBJECTIVES

TUBA4A pathogenic variants are associated with ALS, frontotemporal dementia, spastic ataxia, spasticity, ataxia, Parkinson's disease, female infertility, macrothrombocytopenia, and myopathy. Four recently reported patients with TUBA4A neonatal/childhood onset myopathy had also a decrement on repetitive nerve stimulation (RNS), but such a finding was not further characterized. We describe a patient with a TUBA4A pathogenic variant with adulthood-onset genetic myasthenic syndrome accompanied by myopathy and infertility to highlight the neuromuscular junction defect as the main feature of the patient's phenotype.

METHODS

We reviewed the patient's clinical and laboratory findings and performed transcriptomic analysis on the patient's muscle.

RESULTS

A 53-year-old woman with infertility of unknown etiology manifested fatigability and proximal upper limb muscle weakness in her mid-30s, followed by lower limb involvement. Her examination showed proximal muscle weakness and fatigability but spared facial muscles. CK values were mildly elevated. Anti-AChR, MuSK, P/Q-type calcium channel, and LRP4 antibodies were absent. 2 Hz RNS showed decrement (-14% to -48%) in limb muscles that improved with 3,4-dyaminopyridine (3,4-DAP). Facilitation (231%) occurred in the trapezius. Muscle biopsy showed patchy loss of oxidative enzyme reactivity and no C5b9 or IgG at neuromuscular junctions. Whole genome sequencing identified a heterozygous known TUBA4A pathogenic variant (c.850G>A, p.Glu284Lys). Patient improved with 3,4-DAP and albuterol.

DISCUSSION: TUBA4A p.Glu284Lys can lead to treatable myasthenic syndrome with postsynaptic and likely presynaptic involvement, as suggested by the patient's electrophysiological findings and response to therapy. This patient expands the TUBA4A-disorder spectrum to include overlapping myasthenic syndrome-myopathy and shows that neuromuscular disease and infertility can occur within the same patient.