Genetic testing in inherited ataxias

A review of quality of life after predictive testing for and earlier identification of neurodegenerative diseases

The past decade has witnessed an explosion of evidence suggesting that many neurodegenerative diseases can be detected years, if not decades, earlier than previously thought. To date, these scientific advances have not provoked any parallel translational or clinical improvements. There is an urgency to capitalize on this momentum so earlier detection of disease can be more readily translated into improved health-related quality of life for families at risk for, or suffering with, neurodegenerative diseases. In this review, we discuss health-related quality of life (HRQOL) measurement in neurodegenerative diseases and the importance of these "patient reported outcomes" for all clinical research. Next, we address HRQOL following early identification or predictive genetic testing in some neurodegenerative diseases: Huntington disease, Alzheimer's disease, Parkinson's disease, Dementia with Lewy bodies, frontotemporal dementia, amyotrophic lateral sclerosis, prion diseases, hereditary ataxias, Dentatorubral-pallidoluysian atrophy and Wilson's disease. After a brief report of available direct-to-consumer genetic tests, we address the juxtaposition of earlier disease identification with assumed reluctance toward predictive genetic testing. Forty-one studies examining health-related outcomes following predictive genetic testing for neurodegenerative disease suggested that (a) extreme or catastrophic outcomes are rare; (b) consequences commonly include transiently increased anxiety and/or depression; (c) most participants report no regret; (d) many persons report extensive benefits to receiving genetic information; and (e) stigmatization and discrimination for genetic diseases are poorly understood and policy and laws are needed. Caution is appropriate for earlier identification of neurodegenerative diseases but findings suggest further progress is safe, feasible and likely to advance clinical care.

Clinical clues to differentiating inherited and noninherited etiologies of childhood ataxias

OBJECTIVE

To identify clinical features at presentation that differentiate inherited and noninherited etiologies of childhood ataxias.

STUDY DESIGN

A retrospective chart review analysis was conducted on 167 patients evaluated in neurology outpatient clinics for ataxia or ataxia-related symptoms. The frequency of clinical features, determined a priori, in the 2 groups was compared.

RESULTS

A larger proportion of patients were diagnosed with a nongenetic cause than with a genetic cause (89% [148 patients] vs 11% [19 patients]). The majority of patients in the nongenetic group (56% [83/148]) presented early for medical evaluation, compared with 31% (6/19) in the genetic group. Consanguinity (16% vs 4%) and positive family history (16% vs 2%) were more frequent in the genetic group. Presenting symptoms of abnormal gait (95% vs 57%) and muscle weakness (47% vs 8%), including physical findings of abnormal muscle tone (63% vs 32%), abnormal reflexes (63% vs 16%), clonus (26% vs 9%), dysmetria (32% vs 5%), pes cavus (21% vs 1%), sensory deficits (16% vs 0%), and nonneurologic musculoskeletal abnormalities (58% vs 19%), were more prevalent in the genetic group.

CONCLUSION

Certain clinical features can help delineate between inherited and noninherited causes of childhood ataxia and thus guide physicians in the targeted evaluation of patients.

The spinocerebellar ataxias

Slowly progressive ataxia accompanied by cerebellar degeneration is often genetic in origin. The past 15 years have witnessed a revolution in our understanding of the causes of dominantly inherited ataxias, now known as the spinocerebellar ataxias (SCAs). Nearly 30 distinct genetic causes of SCA are known, numbered chronologically in order of discovery. All SCAs display classic cerebellar signs, and many display disabling noncerebellar features, most commonly brainstem dysfunction. Eye movement abnormalities are common, reflecting cerebellar and brainstem degeneration. Visual loss from retinal degeneration is rare in SCA, occurring most commonly and profoundly in SCA7. Although the SCAs are relentlessly progressive and currently untreatable, recent scientific advances have begun to shed light on various disease mechanisms that may lead to preventive therapies.