Neurogenetics and genetic and genomic testing

Jacinda B Sampson MD PhD (

Dr. Sampson of Stanford University is a co-investigator for clinical trials sponsored by Bristol Meyers Squibb, Expansion therapeutics, PTC Therapeutics, and Sarepta.

)
Jill Goldman MS MPhil CGC (Jill Goldman of Columbia University Medical School has no relevant financial relationships to disclose.)
Aravindhan Veerapandiyan MD, editor. (

Dr. Veerapandiyan of University of Arkansas for Medical Sciences has no relevant financial relationships to disclose.

)
Originally released September 27, 2013; last updated October 7, 2019; expires October 7, 2022

Overview

Neurogenetics encompasses heritable disorders in all the subspecialties of neurology and is an ever-growing field. New technologies such as next-generation sequencing (including whole exome or whole genome sequencing) are expanding testing options, discovering new mutations, and creating challenges in counseling, interpreting, and reporting results to the patient. Yet, next-generation sequencing does not detect many neurogenetic disorders. This article summarizes the types of genetic tests currently available and the resources for choosing appropriate and economical testing are discussed.

Key points

 

• Deciding on the genetic tests to order can be simplified by narrowing the differential diagnosis and defining the patient's phenotype.

 

• Next-generation sequencing of the whole exome is useful for testing for multiple candidate genes simultaneously or for discovering new, rare disorders.

 

• Whole exome sequencing is not suitable for detecting polynucleotide repeat disorders or large insertion/deletions.

 

• Genetic counseling, informed consent, and insurance preauthorization must be obtained before performing genetic testing.

Historical note and terminology

Genetic disorders affecting the nervous system typically present first to the general neurologist at any point in the patient's lifespan. Neurogenetic disorders are a component of every neurologic subspecialty. The heritable nature of certain neurogenetic disorders was appreciated well before the discovery of DNA. Diagnosis by biochemical assays for metabolic and enzymatic defects, or histologic changes on muscle biopsy well preceded the description of DNA. Indeed, the precedent for treatment of neurogenetic disorders with metabolic defects began before clinical genetic tests became available.

Table 1. Timeline of Therapies of Neurogenetic Disorders

Year therapy
reported

Disease

Symptom

Intervention

1930a

Phenylketonuria

Cognitive decline

Dietary restriction, phenylalanine (Alonso-Fernandez and Colon 2009)

1965

Porphyria

Episodic neurologic symptoms-including seizure, neuropathy

Avoidance of precipitating medications (Granick 1966)

1972

Wilson disease

Neurodegeneration, liver failure

Chelation therapy (Walshe 1973)

1982

Metachromatic leukodystrophy

Cognitive decline, neuropathy

Bone marrow transplant (Bayever and Ladisch 1985)

1994

Duchenne muscular dystrophy

Muscle degeneration, cardiomyopathy

Corticosteroids (Karpati and Acsadi 1994)

1998

Fabry disease

Stroke, cardiomyopathy, renal failure

Enzyme replacement (Schiffmann et al 2001)

1999

Pompe disease

Respiratory failure from muscular dystrophy

Enzyme replacement (Amalfitano et al 2001)

2015

Nonsense-mediated Duchenne muscular dystrophy

Slow decline in walking speed

Ataluren (Bushby et al 2014; Haas et al 2015)

2016

Exon 51-skip amenable Duchenne muscular dystrophy

Increased dystrophin expression

ExonDys51 (Mendell et al 2013)

2016

Spinal muscular atrophy

Increased survival motor neuron (SMN) expression

Nusinersen (Finkel et al 2017)

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