Neurological conditions

Neurological conditions

PRACTICE POINT

A small number of adult-onset neurological conditions are due primarily to a single gene mutation A pathogenic variant is a genetic variant that increases an individual’s susceptibility or predisposition to certain diseases. Pathogenic variants are also known as mutations. (eg Huntington disease). There are some more common neurological and neuromuscular conditions that have subsets due to specific gene variants Gene variants are small DNA sequence changes (ie additions, duplications, deletions, substitutions). These variants can have a range of effects: some may cause disease (pathogenic variant), while others do not cause disease but may modify an individual’s risk of disease (i.e may increase risk or provide a protective effect). The vast majority of gene variants are benign and do not result in disease but rather contribute to the differences between people. (eg early-onset Alzheimer disease and early-onset Parkinson disease). 

Positive family history is important in diagnosing neurological conditions with a genetic cause (neurogenetic conditions). Relevant history includes:

  • two or more family members affected with the same condition
  • a significantly earlier age of onset than average (ie <50 years old for Parkinson disease and <65 years old for Alzheimer disease).

What do I need to know?

There are some neurological conditions that are caused by single gene variants that affect the normal function of muscles and the nervous system (eg neuropathies, myopathies, muscular dystrophies, ataxias). There are also a large number of complex neurological conditions caused by an interplay of genetic and environmental factors.

Genetic studies continue to identify variants that contribute to complex neurological conditions; however, genetic testing is generally arranged by specialists for these conditions.

Genetic testing

Genetic testing (diagnostic testing and predictive testing Pre-symptomatic testing aims to determine whether a person will almost certainly develop a particular genetic condition at some point in the future when symptoms of the condition have not yet manifested (eg Huntington disease). Predictive testing aims to determine whether a person who has no signs or symptoms of a specific condition at the time of testing has a specific pathogenic variant that increases the likelihood they will later develop the condition. Predictive testing is often performed in relation to genetic conditions that are not evident at birth, but have their onset during adulthood, such as some cancers (eg BRCA 1 and 2 testing). Predictive genetic testing in familial cancer syndromes can only be conducted when the family-specific genetic variant is known. Hence, genetic testing must generally first be done on a family member affected with the specific condition. ) is available through specialist services for the following conditions:

  • Creutzfeldt–Jakob disease and other prion diseases
  • familial and/or early onset dystonia
  • early onset (50 years) Parkinson disease
  • familial epilepsy
  • familial motor neurone disease
  • Friedreich ataxia
  • hereditary peripheral neuropathies (Charcot–Marie–Tooth disease)
  • hereditary spastic paraparesis
  • Huntington disease
  • mitochondrial disorders
  • muscular dystrophies
  • myotonic dystrophy
  • spinal muscular atrophy
  • spinocerebellar ataxias 

When should I refer?

Individuals with suspected neurological conditions should be referred to a neurologist for clinical diagnosis, which may include genetic testing.

Referral to genetics services for predictive genetic testing of asymptomatic family members is appropriate in cases where:

  • there is a family history of an inherited neurological or neuromuscular condition (diagnosed clinically or by genetic testing)
  • there is a suggestive family history as indicated by the presence of
    • two or more family members affected with the same condition
    • a significantly earlier age of onset than average

Further reading

  • Genetic testing in dementia-A medical genetics perspective Int J Geriatr Psychiatry. 2021 Aug;36(8):1158-1170. doi: 10.1002/gps.5535.
  • The Role of Genetic Testing for Parkinson's Disease. Curr Neurol Neurosci Rep. 2021 Mar 8;21(4):17. doi: 10.1007/s11910-021-01100-7. Lola Cook , Jeanine Schulze , Anna Naito , Roy N Alcalay 
  • Genetic Testing in Epilepsy. Semin Neurol. 2020 Dec;40(6):730-738. doi: 10.1055/s-0040-1719070. Epub 2020 Nov 11. David M Ritter, Katherine Holland.
  • Human Genetics Society of Australasia Position Statement: Predictive and Presymptomatic Genetic Testing in Adults and Children. Twin Research and Human Genetics (2020), 23, 184–189 doi:10.1017/thg.2020.51

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