Cylindrical spirals in two families: Clinical and genetic investigations.

Cylindrical spirals are a rare ultrastructural finding on muscle biopsy, with fewer than 20 reported cases since its first description in 1979. These structures are sometimes observed with tubular aggregates and are thought to comprise longitudinal sarcoplasmic reticulum. While mutations in genes encoding key components of Ca2+ handling (ORAI1 and STIM1) underlie tubular aggregate myopathy, no causative genes have been associated with cylindrical spirals. Here we describe two families with cylindrical spirals on muscle biopsy with a suspected genetic cause. In one family we identified a known truncating variant in EBF3, previously associated with a neurodevelopmental disorder. The affected individuals in this family present with clinical features overlapping with those described for EBF3 disease. An isolated proband in the second family harbours bi-allelic truncating variants in TTN and her clinical course and other features on biopsy are highly concordant for titinopathy. From experimental studies, EBF3 is known to be involved in Ca2+ regulation in muscle, thus EBF3 dysregulation may represent a novel mechanism of impaired Ca2+ handling leading to cylindrical spirals. Additional cases of EBF3 disease or titinopathy with cylindrical spirals need to be identified to support the involvement of these genes in the pathogenesis of cylindrical spirals.

Transcription-terminating mutation in telethonin causing autosomal recessive muscular dystrophy type 2G in a European patient.

A 27-year-old woman of Moldavian origin presented at the age of 15 with progressive proximal limb weakness and painful cramps in her calf muscles. Clinical examination revealed prominent muscle weakness in proximal muscles of the lower extremities and distal anterior compartment of legs, and mild weakness in shoulder girdle muscles. In addition, she had marked calf hypertrophy, muscle atrophy involving the anterior and posterior compartments of the thighs, and the distal anterior compartment of legs, as well as mild scapular winging and hyperlordosis. A muscle biopsy taken from the biceps brachii showed mild dystrophic changes, absent vacuoles, and abundant lobulated fibers. Immunofluorescence and Western blot assays demonstrated complete telethonin deficiency. Molecular analysis revealed a homozygous Trp25X mutation in the telethonin (TCAP) gene resulting in termination of transcription at an early point. Four families from Brazil with telethonin deficiency have previously been reported and classified as LGMD2G, but the actual frequency of this disease is unknown. With this current identification of a case outside the Brazilian population, telethonin mutation-associated LGMD should be considered worldwide.