Laing distal myopathy with a novel mutation in exon 34 of the MYH7 gene

•We describe a new mutation in a four generation family with Laing myopathy in MYH7.•There was complete a segregation between clinical and MRI signs and molecular genetic findings.•Similarities to Charcot-Marie-Tooth disease delayed the correct diagnosis of Laing distal myopathy.•Some of the characteristic signs of this myopathy may only be found at higher age.

We investigated a four-generation family of German ancestry with distal myopathy. Four individuals in two generations were affected. Foot and toe extensor paresis progressing very slowly over decades was the core neurological sign, reflected by fatty infiltration of the lower leg extensor muscles on muscle MRI. Additionally, finger extensor paresis was present in two patients and quadriceps muscle paresis in one. Distal sensory signs had initially given rise to the diagnosis of axonal Charcot-Marie-Tooth (CMT) disease. Two patients had extended verrucae of their foot sole, which may or may not be part of the disease spectrum. All four patients had a novel c.4645G > C mutation in exon 34 of the MYH7 gene that was not present in three clinically unaffected family members. Muscle biopsy of one patient revealed a myopathic pattern associated with type 1 muscle fibre atrophy and core-like lesions in many muscle fibres consistent with a myosin-related myopathy. We conclude that some of the typical clinical signs such as extensor weakness of the big toe and the little finger may only develop in the further course of the disease.