Mutational and clinical spectrum in a cohort of Chinese patients with hereditary nemaline myopathy

Abstract

Hereditary nemaline myopathy (NM) is one of the most common congenital myopathies with the histopathological findings of nemaline bodies. We used targeted nextgeneration sequencing to identify causative mutations in 48 NM patients with confirmed myopathological diagnosis, analyze the mutational spectrum and phenotypic features. Furthermore, reverse transcription polymerase chain reaction (RT-PCR) was used to confirm the pathogenic effect of one nebulin (NEB) splicing variant. The results showed that variants were found in five NM-associated genes, including NEB, actin alpha 1 (ACTA1), troponin T1, Kelch repeat and BTB domain-containing 13, and cofilin-2, in 34 (73.9%), 7 (15.2%), 3 (6.5%), 1 (2.2%), and 1 (2.2%) patients, respectively, in a total of 46/48 (95.8%) NM patients. Of the total 64 variants identified, 51 were novel variants including 26 pathogenic, 1 probably pathogenic, and 24 variant of uncertain significance (VUS). Notably, one NEB splicing mutation, c.21417 +3A>G causing exon 144 splicing (NM_001164508.1), as confirmed by RT-PCR, was found in 52.9% (18 patients) of NEB variant-carrying patients. Typical congenital NM, the most common clinical subtype (60.4%), was associated with five NM genes. We concluded that hereditary NM showed a highly variable genetic spectrum. NEB was the most frequent causative gene in this Chinese cohort, followed by ACTA1. We found a hotspot splicing mutation in NEB among Chinese cohort. K E Y W O R D SChinese, genotype, hereditary nemaline myopathy, phenotype

Differential inclusion ofNEBexons 143 and 144 provides insight intoNEB-related myopathy variant interpretation and disease manifestation

“…The c.21522+3A>G splice variant found in our patients has recently been reported in patients with nemaline myopathy (Lee et al, 2017;Wang et al, 2020;Wen et al, 2020).…”

Clinical and molecular characteristics of 26 fetuses with lethal multiple congenital contractures

“…The complex allele identified in CHST14 (c.[403C>G;410T>A], p.[Arg135Gly;Leu137Gln]), and the homozygous variants residing in KLHL7 (c.1261T>A, p.(Cys421Ser)) and KLHL40 (c.270C>G, p.(Tyr90*)), were each reported in separate families also originating from Turkey, suggesting founder effects for these alterations 30–32 . One of the two VUS identified in NEB (c.169_183dup), was previously reported in compound heterozygous state with c.24209_24212dupTGTT variant in a 3‐year‐old boy with congenital nemaline myopathy 33 . The 4 bp deletion in USP14 (c.233_236del, p.(Leu78Glnfs*11)), identified in the original patients included in this study, was previously published and categorized as a “known variant” for the context of this paper 12 .…”

Case report: Homozygous variants of NEB and KLHL40 in two Arab patients with nemaline myopathy

“…The severity of patient 2’s clinical phenotype in association with the abnormal myofibrils and rod bodies identified by the muscular biopsy, supported the molecular findings and certified the diagnosis of a rare severe case of NEM8. When accepted by the family, a muscle biopsy can clarify the gene variant's impact on the structure and functionality of muscle fibers ( Wang et al, 2020 ). The homozygous KLHL40 gene variant, c.1405G>A, may explain the intrauterine fetal death and the other neonatal fetal death previously recorded in this family.…”

“…The incidence of NM is estimated to be 1 in 30,000 births, with a carrier frequency of approximately 1/87 ( Lehtokari et al, 2014 ). The spectrum of clinical phenotypes is very wide, ranging from severe neonatal forms to mild disorders in childhood ( Sewry et al, 2019 ; Wang et al, 2020 ; Wen et al, 2020 ). NMs commonly show slow or no progression of symptoms, and only 16% of severe neonatal cases present with hypotonia, arthrogryposis, cardiomyopathy, and respiratory failure leading to early infant death ( Cassandrini et al, 2017 ).…”