PracticeUpdate Conference Series - SSIEM 2018

Targeted NGS Gene Panel Improves Diagnosis of Hypoglycemia Due to Inborn Errors of Metabolism In childrenwith persistent hypoglycemia, diagnosis of inborn errors of metabolismcan be improved using a targeted next-generation sequencing (NGS) gene panel.

N GS is cost-effective compared with Sanger sequencing of multiple genes and represents a powerful tool for diagnosis of inborn errors of metabolism that present with persistent hypoglycemia, reports an evaluation of NGS sequencing in 64 children. Alfonso M. Maiorana, MD, of the Bambino Gesu Children’s Hospital in Rome, Italy, and colleagues set out to evaluate the impact of NGS in the genetic diagnosis of 64 pediatric patients with persistent hypoglycemia due to inborn errors of metabolism. The 64 children underwent extensive work-up. They were divided into three diagnostic classes: 1. Single candidate gene (n=9) 2. Multiple candidate genes (n=43) 3. No candidate gene (n=12) Subsequently, they were tested via a custom gene panel of 65 targeted genes, which included five disease categories: 1. Hyperinsulinemic hypoglycemia 2. Fatty acid oxidation and ketogenesis defects 3. Ketolysis defects 4. Glycogen storage diseases and other disorders of carbohydrate metabolism 5. Mitochondrial disorders Molecular data were compared with clinical and biochemical data. A proven diagnosis was obtained in 78% of patients suspected of harboring a single candidate gene, in 49% with multiple candidate genes, and in 33% with no candidate genes. The diagnostic yield was 48% for hyperinsulinemic hypoglycemia, 66% per fatty acid oxidation and ketogenesis defect, 59% for glycogen storage diseases and other carbohydrate disorders, and 67% for mitochondrial disorders. Remarkably, a molecular diagnosis was established in 33% of patients belonging to the no candidate gene class.

The causes of negative genetic results include the possibility of detecting variants of unknown significance that have not been definitely linked to the disease, the presence of insertion/deletion of few nucleotides, mutations in novel disease- causing genes as well as mutations in noncoding regions, and the possibility of variant(s) in known disease genes not included on the panel for whom whole exome/genome sequencing approaches would improve the diagnostic yield. In 45% of patients in whom clinical and laboratory evaluation did not allow identification of a single candidate gene, the targeted NGS approach provided a rapid diagnosis, overtaking genetic heterogeneity and clinical variability. A further advantage of NGS is its cost-effectiveness versus traditional Sanger sequencing. Single- gene testing, the traditional approach for genetic diagnosis, is appropriate in selected cases that present with specific clinical and biochemical features. Use of a gene panel eliminates the hurdle of having to prioritize multiple candidate genes for stepwise sequencing. NGS analysis also confers better accuracy and higher sensitivity in mosaicism detection than Sanger sequencing. The approach also helps avoid invasive, inaccurate, or expensive procedures, such as liver biopsy and enzyme assay.

PRACTICEUPDATE CONFERENCE SERIES • SSIEM 2018 10