Nemaline myopathy type 8 caused by KLHL40 gene in a twin: case report and literature review / 中华围产医学杂志

ABSTRACT

Objective:To investigate the clinical, genetic, and pathological features of nemaline myopathy type 8 (NEM8) caused by KLHL40 gene variation. Methods:The clinical data, gene sequencing results, and musculoskeletal pathophysiology of two cases (a pair of twins) with NEM8 admitted to our hospital in July 2022 were collected. CNKI, VIP, Wanfang, Yiigle, PubMed, Embase, and Web of Science Database were searched with the English and Chinese terms "nemaline myopathy type 8", "nemaline body myopathy type 8", and " KLHL40" from January 2007 to February 2023. The clinical, genetic, and musculoskeletal characteristics of the NEM8 cases were summarized using the descriptive statistical analysis method. Results:(1) Case report: The mother (G2P2) of the twins (Ⅳ-2 and Ⅳ-3) was conceived by IVF-embryo transfer and delivered at 37 +1 gestational weeks. The two cases were dizygotic twins whose maternal grandmother had lip and palate cleft. The first baby (Ⅳ-1) of the woman exhibited absent left pinna, contracture at the end of both fingers, talipes equinovarus in both feet and died of respiratory failure two hours after birth. Fetal edema and fetal movement delay in the twins and varus right foot in one twin were found during pregnancy. Both cases developed intrapartum asphyxia with the clinical manifestations of generalized muscle weakness, respiratory failure, dysphagia, multiple joint contractures, and fractures. The families withdrew the treatment and the twins died after maintaining life with ventilators for 53 days after birth. Whole exome sequencing of the pedigree found c.1779G>T (p.W593C) homozygous variants of the KLHL40 gene in the twins and c.1779G>T (p.W593C) heterozygous variants of the KLHL40 gene in the parents, both were de novo. Musculoskeletal pathophysiology indicated that muscle fibers are thin and round with a fetal shape and absent rod. (2) Literature review: Among the 29 cases of NEM8, including two current cases and 27 cases retrieved from 15 papers, eight cases terminated the pregnancies, and 21 were live births; seven cases (24.1%) with positive family history; 19 cases (65.5%) were found with abnormalities during pregnancy, including abnormal fetal movements, polyhydramnios, joint contracture, and fetal edema. Of the 21 live births, 20 cases had intrapartum asphyxia, 21 had postnatal respiratory failure, 20 had generalized muscle weakness, and 19 had dysphagia. Among the 29 cases, 17 cases (58.6%) were homozygous variants of the KLHL40 gene, and 12 cases (41.4%) were compound heterozygous variants. The detection rate of c.1516A>C(p.Thr506Pro) was the highest [72.4% (21/29)], followed by c.602G>A(p.Trp201*) [17.2% (5/29)]. Out of the 15 cases who underwent musculoskeletal pathological examination, all had abnormal muscle fiber size and morphology; 10 cases had rods. Conclusions:NEM8 should be considered for those with abnormal fetal movements, polyhydramnios, joint malformation, fetal edema during the fetal period and failure to establish respiration at birth as well as postnatal generalized muscle weakness, respiratory failure, dysphagia, multiple joint contractures, and fracture. Moreover, genetic detection should be performed as soon as possible. NEM8 can be diagnosed in ones with KLHL40 gene homozygous or compound heterozygous variants and musculoskeletal pathological results of abnormal size and shape of muscle fibers, regardless of the presence of rods.