New generation genetic testing entering the clinic

Abstract

New generation sequencing (NGS) genetic testing is a powerful diagnostic tool and is increasingly used in the clinical workup of patients, especially in unusual presentations or where a positive family history suggests heritable disease. This review addresses the NGS technologies Targeted sequencing (TS), Whole exome sequencing (WES), Whole genome sequencing (WGS), and the use of gene panels or gene lists for clinical diagnostic purposes. These methods primarily assess nucleotide sequence but can also detect copy number variants and many tandem repeat expansions, greatly simplifying diagnostic algorithms for movement disorders. Studies evaluating the efficacy of NGS in diagnosing movement disorders have reported a diagnostic yield of up to 10.1% for familial and 15.7% for early-onset PD, 11.7–37.5% for dystonia, 12.1–61.8% for ataxia/spastic paraplegia and 11.3–28% for combined movement disorders. Patient selection and stringency in the interpretation of the detected variants and genotypes affect diagnostic yield. Careful comparison of the patient's or family's disease features with the previously reported phenotype associated with the same variant or gene can avoid false-positive diagnoses, although some genes are implicated in various phenotypes. Moving from TS to WES and WGS increases the number of patients correctly diagnosed, but for many patients, a genetic cause cannot be identified today. However, new genetically defined entities are discovered at rapid pace, and genetic databases and our knowledge of genotype-phenotype correlations expand steadily. We discuss the need for clear communication of genetic results and suggest a list of aspects to consider when reporting neurogenetic disorders using NGS testing.