Clinical and molecular analysis of nine fetal cases with clinically significant variants causing nemaline myopathy

Genetic diseases underlying a spectrum of fetal effusions

OBJECTIVES

Nonimmune hydrops fetalis is well understood to be heterogenous and the common endpoint of many genetic diseases. However, less is known about the prevalence and presenting features of genetic diseases that underlie other types of fetal effusions such as single effusions, leaving uncertainty in clinical practice about optimal approaches to testing and counseling for these pregnancies. We aimed to determine the diagnostic yield of exome sequencing by type of fetal effusion and presence of concurrent structural abnormalities and to identify the unique presenting features of underlying genetic diseases.

STUDY DESIGN

We conducted a prospective cohort study of pregnancies with nonimmune hydrops fetalis and other fetal effusions, with participants enrolled from across the United States. Inclusion criteria were nondiagnostic results of chromosomal microarray and/or karyotype and the presence of at least 1 fetal effusion, including nuchal translucency ≥3.5 mm, cystic hygroma, pleural effusion, pericardial effusion, ascites, and/or skin edema. Exome sequencing was performed by our institution's Clinical Laboratory Improvement Amendments-approved laboratory and results were returned to participants and their providers. Detailed fetal phenotypic data were ascertained and used to inform genetic variant interpretation, including fetal imaging findings (ultrasound, magnetic resonance imaging, and echocardiogram), pathology reports, and laboratory reports. Pregnancies with a variant or variants classified as pathogenic or likely pathogenic were considered diagnostic or positive. The primary outcome was the diagnostic yield of exome sequencing by the type of fetal effusion, with and without concurrent structural abnormalities. Secondary outcomes were the types of fetal effusions observed by category of genetic disease.

RESULTS

In all, 118 pregnancies with nonimmune hydrops fetalis and other effusions underwent exome sequencing and 23% (27/118) had positive (diagnostic) findings. Pregnancies with nonimmune hydrops fetalis with and without concurrent structural abnormalities had diagnostic yields of 21% (9/42) and 40% (6/15), respectively (P=.15). Single effusions such as pleural effusion with and without concurrent structural abnormalities had diagnostic yields of 23% (6/26) and 17% (1/6), respectively (P=.61). The diagnostic yield for increased nuchal translucency or cystic hygroma was significantly greater for pregnancies with concurrent structural abnormalities (42%, 5/12) compared to those without (0%, 0/17, P<.01). We further observed numerous patterns in terms of how genetic diseases present in utero, such as RASopathies and musculoskeletal disorders demonstrating all types of effusions, while other disorders marked by neurodevelopmental delays after birth demonstrated all types of effusions except for nonimmune hydrops fetalis.

CONCLUSION

The diagnostic yield of exome sequencing was high across all types of effusions including single effusions with and without concurrent structural abnormalities, with the exception of isolated increased nuchal translucency or cystic hygroma. Furthermore, we observed numerous patterns in terms of how genetic diseases present in utero with fetal effusions. These findings contribute important information for counseling and clinical management, highlight the utility of exome sequencing for fetal effusions beyond nonimmune hydrops fetalis, and inform accurate results of phenotype-driven tests such as exome sequencing.

The widening genetic and myopathologic spectrum of congenital myopathies (CMYOs): a narrative review

Congenital myopathies (CMYOs) represent a genetically and clinically heterogeneous group of disorders characterized by early-onset muscle weakness and distinct myopathologic features. The advent of next-generation sequencing (NGS) has accelerated the identification of causative genes, leading to the discovery of novel CMYOs and thereby challenging the traditional classification. In this comprehensive review, we focus on the clinical, myopathologic, molecular and pathophysiological features of 33 newly identified CMYOs.

Novel variant in ACTA1 identified in a fetus with akinesia deformation sequence and cortical development delay

We present a case of fetal akinesia deformation sequence due to nemaline myopathy (NM). In addition to the muscle manifestations, prenatal observations included an enlarged subarachnoid space and delayed cortical development. Trio whole-exome sequencing revealed a de novo novel pathogenic variant in the ACTA1 gene, which encodes skeletal muscle alpha-actin. Our findings suggest that brain abnormalities can occur prenatally in NM and support the potential role of skeletal muscle alpha-actin in the central nervous system.

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.