A novel mutation in NEB causing foetal nemaline myopathy with arthrogryposis during early gestation

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

OBJECTIVE

To present the prenatal features and postnatal outcomes of pregnancies with fetal nemaline myopathy (NM).

STUDY DESIGN

This was a retrospective study of nine cases with NM diagnosed by prenatal or postnatal clinical features and confirmed by genetic testing. Clinical and laboratory data were collected and reviewed for these cases, including maternal demographics, prenatal sonographic findings, exome sequencing (ES) results, and pregnancy outcomes.

RESULTS

All of the nine cases were detected to have NM-causing variants, involving NEB gene in 2 cases, ACTA1 in 3 cases, KLHL40 in 3 cases, and TPM2 in 1 case. Almost all (8/9) had normal first-trimester ultrasound scans except one who had an increased nuchal translucency. Seven (7/9) cases had second-trimester abnormal ultrasounds with fetal akinesia and/or extremity anomalies. Two (2/9) had only third-trimester abnormal ultrasounds with fetal akinesia and polyhydramnios, with one combined with fetal growth restriction. Four pregnancies with a positive prenatal ES were terminated, while five having not receiving prenatal ES continued to term. Only one infant survived 1 year old, and four passed away within 12 months.

CONCLUSION

Prenatal ultrasound can detect clues that lead to the diagnosis of NM, such as reduced or absent fetal movements, polyhydramnios and extremity anomalies.

Case report: identification of one frameshift variant and two in cis non-canonical splice variants of NEB gene in prenatal arthrogryposis

NEB mutation is associated with congenital nemaline myopathies. Here, we report a family with recurrent prenatal arthrogryposis. Trio whole exome sequencing (WES) disclosed three novel NEB (NM_001271208.2) variants including one paternal frameshift c.19049_19050delCA (p.Thr6350Argfs*14) and two double maternal variants in cis c. [24871G>T;24871-10C>G] (p. [Val8291Phe;?]). They are evaluated as "likely pathogenic (LP)", "variant of uncertain of significance (VUS)", and "VUS", respectively. After further prediction, the c.24871G>T, c.24871-10C>G, and c.[24871G>T;24871-10C>G] were respectively genetically engineered into the three plasmids. Compared with their wild-type counterparts, the three plasmids all produced truncated transcripts, and also a significant proportion of the full-length transcripts, which allowed us to reclassify NEB c.24871G>T and c.24871-10C>G variants as LP. As far as we know, this is the first case carrying NEB allele-specific function of partial loss. This result helped the couple make informed reproductive choices and opt for assisted reproduction for future pregnancies. This study also increased awareness to the phenotype of prenatal nemaline myopathy and expanded the variant spectrum of NEB.

Identification of genetic alterations in couples and their products of conceptions from recurrent pregnancy loss in North Indian population

Background: Recurrent pregnancy loss (RPL) is one of the most common pregnancy-related complications, which can be stressful and emotionally draining for a couple. Genetic alterations, which are responsible for RPL, can be present in either of the three genomes: mother, father, or their fetuses. In addition, environmental factors interacting with these three genomes can affect germline cells. With this aim, the present study was conducted to understand the underlying etiology of RPL using Next-generation sequencing (NGS; couple exome and TRIO exomes) in combination with cytogenetic tests [karyotyping and chromosomal microarray (CMA)]. Material & Methods: In present study we recruited 61 couples with RPL (history of ≥ 2 abortions) and 31 products of conceptions (POCs). For all couples karyotyping was done at the time of recruitment, followed by collection of POC samples and parental blood samples. Before processing POC samples for CMA, they were checked for maternal cell contamination (MCC) by QF-PCR. In POC samples with no pathogenic variant, TRIO exome sequencing was done. Further, in case of unavailability of POC sample, couple exome sequencing was done for RPL couples. Results: In six individuals out of 61 couples (5%), abnormality in karyotypes was detected. Among 116 normal karyotypes, there were 11 heteromorphisms (9.5%), for which the couples had to be counselled and reassured. Out of the 31 POCs, 10 were excluded because of MCC (around 30%) and one had major aneuploidy. CMA in POCs identified pathogenic copy number variations (CNVs) in 25% of cases (5/20) and variant of unknown significance (VUS) in 20% of cases (4/20). Autosomal trisomy was the most frequent chromosomal abnormality diagnosed. NGS was performed to establish single-gene causes of RPL. Couple exome sequencing was performed in 20 couples, and 14 were found to be carriers for autosomal recessive conditions. A total of 50 potential disease-causing variants in 40 genes were identified in 33 of 40 individuals (82.5%). Putative causative variants were identified in 37.5% of the TRIO cases (3/8). Mutations in few important genes (SRP54, ERBB4, NEB, ALMS, ALAD, MTHFR, F5, and APOE), which are involved in vital pathways, early embryonic development, and fetal demise, were identified in the POCs. Conclusion: It enhances our understanding of prenatal phenotypes of many Mendelian disorders. These mutated genes may play an auxiliary role in the development of treatment strategies for RPL. There was no correlation of the number of abortions with etiological yield of any technique to detect the cause of RPL. This study shows the utilization of combination of techniques in improving our understanding of the cause of early embryonic lethality in humans.

Case Report: Prenatal Diagnosis of Nemaline Myopathy

Nemaline myopathy (NM) is a rare, hereditary heterogeneous myopathy. Fetal NM has a more severe disease course and a poorer prognosis and is usually lethal during the first few months of life. Hence, early prenatal diagnosis is especially important for clinical interventions and patient counseling. We report the case of a fetus with NM due to KLHL40 gene variation leading to arthrogryposis multiplex congenita (AMC). The ultrasonography and histopathology results revealed an enhanced echo intensity and decreased muscle thickness, which may be novel features providing early clues for the prenatal diagnosis of NM. Moreover, to our knowledge, this article is the first report to describe a case of NM associated with complex congenital heart disease (CHD).