Expanding the phenotypic spectrum of COL6-related diseases: Motor neuropathy-like and neuromyopathy associated with COL6A3 c.7447A>G.

Abstract

Collagen VI is a key component of the extracellular matrix. Murine models suggest that it regulates Schwann cell differentiation, peripheral nerve myelination and regeneration after injury. Neuropathic findings in COL6-related dystrophies (COL6-RDs) have been rarely reported, often based on electromyography findings without nerve conduction abnormalities. We report 37 patients (1.5-79 years), from 32 different families, carrying the COL6A3-c.7447A>G variant, presenting with neuropathic/neuromyopathic findings. Most patients presented in the first decade of life with an abnormal gait and frequent falls (54%), delayed motor milestones (32%) and foot deformities (19%). Predominant distal weakness was present in 46% of patients, whereas 27% exhibited proximo-distal involvement. Foot deformities were present in 32%; joint contractures were present in 83%, exclusively affecting lower limbs in 49%. At last evaluation, mild restrictive respiratory insufficiency was diagnosed in 1 patient and nocturnal hypoventilation requiring non-invasive ventilation in 2. Most patients (89%) remained ambulant at last assessment. Nerve conduction studies (n=29) revealed reduced lower-limb CMAP amplitudes in 79%. Needle EMG (n=31) revealed chronic neurogenic-like features in 84% and mixed neuromyogenic features in 13%. Muscle biopsy (n=12) demonstrated features suggestive of neuropathic involvement in 4 (33%) and mixed neuropathic-myopathic features in 5 (42%). Muscle imaging (n=23) revealed a typical COL6-RD pattern in 48% (with severe distal lower limb atrophy in 65%), and isolated or predominant distal atrophy in 30%. Inheritance was autosomal recessive in all cases. The COL6A3-c.7447A>G variant was present in homozygosity in 24 (65%) and in compound heterozygosity with a second COL6A3 variant in 13 (35%), including 8 previously unreported. We report an expanding phenotypic spectrum associated with COL6-RD, underscoring its relevance in the diagnostic evaluation of distal motor neuropathy-like or neuromyopathic presentations.