Founder Mutation c.1516A>C in KLHL40 Is a Frequent Cause of Nemaline Myopathy With Hyponatremia in Ethnic Chinese

KLHL40-Related Myopathy: A Systematic Review and Insight into a Follow-up Biomarker via a New Case Report

BACKGROUND

Mutations in the KLHL40 gene are a common cause of severe or even lethal nemaline myopathy. Some cases with mild forms have been described, although the cases are still anecdotal. The aim of this paper was to systematically review the cases described in the literature and to describe a 12-year clinical and imaging follow-up in an Italian patient with KLHL40- related myopathy in order to suggest possible follow-up measurements.

METHODS

Having searched through three electronic databases (PubMed, Scopus, and EBSCO), 18 articles describing 65 patients with homozygous or compound heterozygous KLHL40 mutations were selected. A patient with a KLHL40 homozygous mutation (c.1582G>A/p.E528K) was added and clinical and genetic data were collected.

RESULTS

The most common mutation identified in our systematic review was the (c.1516A>C) followed by the (c.1582G>A). In our review, 60% percent of the patients died within the first 4 years of life. Clinical features were similar across the sample. Unfortunately, however, there is no record of the natural history data in the surviving patients. The 12-year follow-up of our patient revealed a slow improvement in her clinical course, identifying muscle MRI as the only possible marker of disease progression.

CONCLUSIONS

Due to its clinical and genotype homogeneity, KLHL40-related myopathy may be a condition that would greatly benefit from the development of new gene therapies; muscle MRI could be a good biomarker to monitor disease progression.

Novel and recurrent ASPM mutations of founder effect in Chinese population

PURPOSE

Mutations in ASPM are the most common causes of primary microcephaly (MCPH), which is a rare brain developmental disorder with few studies in Chinese population so far. This study aimed to identify the common pathogenic variants of ASPM and estimated the incidence of MCPH5 in Guangxi population.

METHODS

We ascertained six MCPH cases caused by ASPM mutations in Guangxi Zhuang Autonomous Region, Whole-exome sequencing (WES) was performed to uncover the causal variants. The haplotype analysis was used to estimate the age of the recurrent variation.

RESULTS

Five different pathogenic variants were identified in this batch of MCPH5 cases, including two novel variants p.Ser842fs*9 and p.Lys1340Argfs*29. An rarely reported pathogenic variant, c.1789C>T/p.Arg597* was found to be a founder mutation in local population. We evaluated all ASPM variants detected among 2674 non-microcephalic individuals and estimated the MCPH5 incidence to be 5.03/1,000,000 in Guangxi population.

CONCLUSIONS

We reported the first case series of Chinese MCPH cases with ASPM mutation and revealed a highly recurrent founder mutation in this local population. MCPH5 may be the major type of congenital microcephaly in Chinese population.

Clinical and molecular analysis of four unrelated Chinese families with pathogenic KLHL40 variants causing nemaline myopathy 8

Background

Homozygous or compound heterozygous variants in the KLHL40 gene cause nemaline myopathy 8 (NEM8), a severe autosomal recessive muscle disorder characterized by prenatal polyhydramnios, fetal akinesia or hypokinesia, joint contractures, fractures, respiratory failure and dysphagia. Currently, 46 individuals with NEM8 have been described in the literature, and 30 variants in KLHL40 have been identified.

Results

Here, we reported five individuals from four unrelated Chinese families who presented common features of nemaline myopathy and infrequent clinical characteristics. Whole-exome sequencing (WES) was used to identify the causative gene. WES identified a recurrent missense variant c.1516A>C (p.Thr506Pro) and a novel frameshift variant c.543del (p.Ser182Profs*17) in KLHL40 in patient 1, a nonsense variant c.602G>A (p.Trp201*) and a missense variant c.1516A>C (p.Thr506Pro) in KLHL40 in patient 2, and homozygous variant c.1516A>C (p.Thr506Pro) in KLHL40 in patient 3 and both siblings (patients 4 and 5), all of which were confirmed by Sanger sequencing. Next, we estimated the incidence of this disorder in the southern and northern Chinese population to be 4.59/10⁶ and 2.95/10⁶, respectively, based on the cumulative allele frequency of pathogenic variants in internal database.

Conclusion

The results of our study expand the mutation spectrum of KLHL40 and enrich our understanding of the clinical characteristics of NEM8. Genetic counseling was provided for the four families involved in this study. Given the severity and the relatively high incidence of this condition, we strongly suggest that KLHL40 be incorporated into a carrier screening panel for the Chinese population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02306-9.

A novel and recurrent KLHL40 pathogenic variants in a Chinese family of multiple affected neonates with nemaline myopathy 8

BACKGROUND

Nemaline myopathy 8 is a severe autosomal recessive muscle disorder characterized by fetal akinesia or hypokinesia, contractures, fractures, respiratory failure and swallowing difficulties apparent at birth.

METHODS

An affected dizygotic twin pair from a non-consanguineous Chinese family presented with severe asphyxia, lethargy and no response to stimuli. The dysmorphic features included prominent nasal bridge, telecanthus, excessive hip abduction, limb edema, absent palmar and sole creases, acromelia, bilateral clubfoot, appendicular hypertonia and cryptorchidism. Both infants died in the first week of life. Whole-exome sequencing was used to identify the causative gene.

RESULTS

Whole-exome sequencing identified a recurrent missense variant c.1516A>C and a novel splice-acceptor variant c.1153-1G>C in KLHL40 gene in both siblings. We estimated the disease incidence in Southern Chinese population to be 2.47/100,000 based on the cumulative allele frequency of pathogenic and likely pathogenic variants in our internal database.

CONCLUSION

Our study expanded the mutation spectrum of KLHL40 and the condition could have been underdiagnosed before. We identified a recurrent missense variant c.1516A>C and provided evidence further supporting the founder effect of this variant in Southern Chinese population. Given the severity of the condition and the relative high incidence, this not-so-rare disorder should be included in expanded carrier screening panel for Chinese population.

The Role of Cullin-RING Ligases in Striated Muscle Development, Function, and Disease

The well-orchestrated turnover of proteins in cross-striated muscles is one of the fundamental processes required for muscle cell function and survival. Dysfunction of the intricate protein degradation machinery is often associated with development of cardiac and skeletal muscle myopathies. Most muscle proteins are degraded by the ubiquitin-proteasome system (UPS). The UPS involves a number of enzymes, including E3-ligases, which tightly control which protein substrates are marked for degradation by the proteasome. Recent data reveal that E3-ligases of the cullin family play more diverse and crucial roles in cross striated muscles than previously anticipated. This review highlights some of the findings on the multifaceted functions of cullin-RING E3-ligases, their substrate adapters, muscle protein substrates, and regulatory proteins, such as the Cop9 signalosome, for the development of cross striated muscles, and their roles in the etiology of myopathies.

The KLHL40 c.1516A>C is a Chinese-specific founder mutation causing nemaline myopathy 8: Report of six patients with pre- and postnatal phenotypes

Background

Autosomal recessive or compound heterozygous mutations in KLHL40 cause nemaline myopathy 8, which is one of the most severe forms of nemaline myopathy. The KLHL40 c.1516A>C variant has recently been reported as a founder mutation in southern Chinese.

Methods

We report six cases of nemaline myopathy 8 which involves the c.1516A>C variant, from five unrelated families of non‐consanguineous southern Chinese. The pre‐ and postnatal phenotypes of these cases were reviewed with emphasis on prenatal clinical features. Genetic testing for the founder mutation was performed on three patients with homozygous mutations.

Results

Common prenatal features included reduced fetal movement, polyhydramnios, breech presentation, and clubfeet. Two pregnancies were terminated. Four live‐born patients had postnatal features typical of nemaline myopathy 8. The length of survival ranged from 49 days to 17 months, with respiratory failure and infections being the principal causes of death. Haplotype analysis in three patients with homozygous mutation showed a shared haplotype block of 1.1727 cM spanning over the c.1516A>C variant, suggesting it is a southern Chinese‐specific founder mutation.

Conclusion

Analysis of the KLHL40 c.1516A>C variant should be considered in prenatal diagnosis of Chinese pregnant patients with suspected congenital neuromuscular disorders or with significant family history of congenital myopathies.