Genetics research in recent decades has discovered numerous genetic variants that help explain the etiology of developmental disabilities (DDs). Genetic tests (e.g., array comparative genomic hybridization, sequencing) are rapidly diffusing into clinical practice for diagnosing DDs or, more often, for determining their genetic etiology. An urgent need exists for a better understanding of these tests and their clinical utility.
This Technical Brief collects and summarizes information on genetic tests clinically available in the United States to detect genetic markers that predispose to DDs. It also identifies, but does not systematically review, existing evidence addressing the tests' clinical utility. This Brief primarily focuses on patients with idiopathic or unexplained DDs, particularly intellectual disability, global developmental delay, and autism spectrum disorder. Several better-defined DD syndromes, including Angelman syndrome, fragile X syndrome, Prader-Willi syndrome, Rett syndrome, Rubinstein-Taybi syndrome, Smith-Magenis syndrome, velocardiofacial syndrome, and Williams syndrome are also included. Patient-centered health outcomes (e.g., functional or symptomatic improvement) and intermediate outcomes (e.g., changes in clinical decisions or family reproductive decisions, the tests' diagnostic accuracy and analytic validity) are examined.
We sought input from nine Key Informants to identify important clinical, technology, and policy issues from different perspectives. We searched the National Center for Biotechnology Information's Genetic Testing Registry (GTR) to identify genetic tests. A structured search of studies published since 2000 was performed to identify available evidence that addresses genetic tests' clinical utility.
Our search of the GTR database identified 672 laboratory-developed tests offered by 63 providers in 29 States. We also identified one test cleared by the U.S. Food and Drug Administration. Common genetic testing methods used include array comparative genomic hybridization, microarray, DNA sequencing (the Sanger method or next-generation sequencing), and polymerase chain reaction. We did not identify any studies that directly assessed the impact of genetic testing on health outcomes. Most of the clinical studies identified for indirect assessment of clinical utility are case series reporting on a test's diagnostic yield.