New techniques in molecular genetic diagnostics now allow for accurate diagnosis in a large proportion of patients with muscular diseases. Nevertheless, many patients remain unsolved, although the clinical history and/or the muscle biopsy give a clear indication of the involved genes. In many cases, there is a strong suspicion that the cause must lie in unexplored gene areas, such as deep-intronic or other non-coding regions. In order to find these changes, next-generation sequencing (NGS) methods are constantly evolving, making it possible to sequence entire genomes to reveal these previously uninvestigated regions. Here, we present a young woman who was strongly suspected of having a so far genetically unsolved sarcoglycanopathy based on her clinical history and muscle biopsy. Using short read whole genome sequencing (WGS), a homozygous inversion on chromosome 13 involving SGCG and LINC00621 was detected. The breakpoint in intron 2 of SGCG led to the absence of γ-sarcoglycan, resulting in the manifestation of autosomal recessive limb-girdle muscular dystrophy 5 (LGMDR5) in the young woman.

Sarcoglycanopathies (SGCs) which are caused by mutations in SGCA, SGCB, SGCG or SGCD genes are a subgroup of autosomal-recessive limb-girdle-muscular-dystrophies (LGMD2). Although frequencies of mutations in these genes are different among populations, mutations in SGCA and SGCD, respectively, have the highest and lowest frequencies in most populations. Here, we report the proportion of mutations in SGC genes among a group of Iranian SGCs patients. Clinical features and results of SGC genes screening of 25 SGCs probands are presented. Large deletion mutations are confirmed with MLPA assays. In total, 15 candidate disease causing mutations were observed in the SGCA, SGCB, SGCG and SGCD genes; ten were novel. Fourteen (56%), seven (28%), three (12%) and one (4%) patient, respectively, carried mutations in SGCB, SGCG, SGCD and SGCA. The findings suggest that LGMD2E is the most common form of SGCs in the Iranian population and that LGMD2D is the rarest. Twelve LGMD2E cases carried the same mutation. To the best of knowledge, the mutation spectrum in SGCs is being reported for the first time in Iranian population. The finding will be beneficial for screening and genetic-counseling of SGCs patients in Iran.

Limb-girdle muscular dystrophy type 2C (LGMD2C) is considered one of the severe forms of childhood-onset muscular dystrophy. The geographical distribution of founder mutations in the SGCG gene has a prominent effect on the prevalence of LGMD2C in certain populations. The aim of this study was to confirm the hypothesis that the c.787G>A (p.E263K) mutation in the SGCG gene is a founder mutation among Puerto Rican Hispanics and to characterize the associated clinical and immunohistochemical phenotype. Genotyping of six polymorphic microsatellite markers internal to (D13S232) and flanking (D13S175, D13S292, D13S787, D13S1243, D13S283) the SGCG gene was performed on four unrelated Puerto Rican patients with LGMD2C. Preserved ambulation to the second decade of life was observed in at least two subjects. Immunostaining of skeletal muscle demonstrated absence of γ-sarcoglycan in all affected subjects. Two markers, D13S232 and D13S292, were highly informative and confirmed that all four families share the haplotype of the mutant allele. Our findings confirm that the E263K missense mutation in the SGCG gene is a founder mutation in Puerto Rican Hispanics. A slowly progressive disease course with prolonged preservation of ambulation can be seen in association with this mutation, providing evidence for phenotypic variability.