Titinopathies: Phenotype - genotype heterogeneity in an Indian cohort.

Titinopathies are heterogenous group of disorders affecting the skeletal and cardiac muscles variably and caused by Titin (TTN) gene mutations located in Chromosome 2. The manifestations extend from congenital to adult-onset myopathies. Here we describe the phenotype-genotype heterogeneity of patients with myopathy/muscular dystrophy associated with TTN variants in an Indian cohort. A retrospective descriptive study of 12 patients diagnosed with primary muscle disease evaluated between 2016 and 2023 harboring rare TTN variants. Eight patients were included (M:F ratio - 3:1). The median age at onset of entire cohort is 5 (range: birth- 33 years). The major clinical phenotypes were congenital myopathy [n = 3, 37.5%], juvenile onset myopathy [n = 3, 37.5%] and adult AD - Hereditary myopathy with early respiratory failure (HMERF) phenotype [n = 2, P6, P8; 25%]. Prominent / wide first interdigital space in feet in congenital and juvenile forms (c.38421_38437delinsC, c.106531 + 1G > A) was a novel feature. The variant c.95134T > C previously reported in HMERF in British population, was noted in two patients in our cohort and with GNE myopathy like phenotype in one. Muscle MRI done in congenital myopathy (c.26201-1G > A) showed fatty infiltration of anterior and posterior thigh with sparing of gracilis, adductor magnus and tibialis anterior. This is the first Indian study with a large cohort demonstrating many novel mutations and clinical heterogeneity expanding the spectrum of titinopathies.