Utility of next-generation sequencing in genetic testing and counseling of disorders involving the musculoskeletal system—trends observed from a single genetic unit

Background

Disorders involving the musculoskeletal system are often identified with short stature and a range of orthopedic problems. The clinical and genetic heterogeneity of these diseases along with several characteristic overlaps makes definitive diagnosis difficult for clinicians. Hence, using molecular testing in addition to conventional tests becomes essential for appropriate diagnosis and management.

Methods

Comprehensive clinical examination, detailed pretest and posttest counseling, molecular diagnosis with next-generation sequencing (NGS), genotype–phenotype correlation and Sanger sequencing for targeted variant analysis.

Results

This manuscript reports a molecular spectrum of variants in 34 orthopedic cases referred to a single genetic unit attached to a tertiary care hospital. The diagnostic yield of NGS-based tests coupled with genetic counseling and segregation analysis was 79% which included 7 novel variants. In about 53% (i.e. 18/34 cases), molecular testing outcome was actionable since 8 of the 18 underwent prenatal diagnosis, as they were either in their early gestation or had planned a pregnancy subsequent to molecular testing, while ten cases were premaritally/prenatally counseled for the families to take informed decisions as they were in the reproductive age.

Conclusions

The report highlights the importance of NGS-based tests even in a low resource setting as it helps patients, families and healthcare providers in reducing the economic, social and emotional burden of these disorders.

Familial Acute Necrotizing Encephalopathy: Evidence From Next Generation Sequencing of Digenic Inheritance

Infection-induced acute encephalopathies (IIAEs) are a group of neurologic disorders caused post infection. They are of 8 types, 6 of which are herpes specific, whereas IIAE3 and IIAE4 can be triggered by infections additional to herpeslike influenza, enterovirus, etc. IIAE3 is also known as acute necrotizing encephalopathy type 1, which is a rare type of encephalopathy that occurs following an infection in infancy or early childhood. Symptoms include fever, cough, congestion, vomiting, and diarrhea followed by seizures, hallucination, ataxia, and abnormal muscle tone, and sometimes it leads to untimely death. Here, we describe a familial case where 3 siblings were clinically diagnosed with acute necrotizing encephalopathy 1. Genetic testing revealed 2 heterozygous variations: RANBP2 c.5249C>G, p.P1750 R, and CPT2 c.365C>T, p.S122F. Variants in RANBP2 and CPT2 have been individually known to be associated with IIAE3 and IIAE4, respectively. Segregation analysis revealed that the RANBP2 variant was inherited from the father and the CPT2 variant from the mother. This case qualifies to be the first of its kind where digenic inheritance (ie, DNA sequence variants in 2 genes are required for the pathogenic phenotypes) appears to cause a lethal class of acute necrotizing encephalopathy.