A new genetic cause of ataxia

A study by researchers at Weill Cornell Medicine-Qatar (WCM-Q) has revealed a new genetic cause of ataxia and the implications it has for marriage.

Because cerebellar ataxia is often an inherited disease, it could have major implications for the consanguineous marriages that are common in Qatar. When the mutated gene that causes the disorder is expressed in a recessive manner, both parents have to have the same recessive gene for some of their children to be affected. Since genes are inherited, it is much more likely that people within an extended family carry the same genes. Therefore, a consanguineous marriage within a family who carry the mutated recessive gene is much more likely to lead to cerebellar ataxia in the children of that marriage. 

Investigators have now discovered an unusual recessive mutation that leads to cerebellar ataxia.

The study was launched after a young woman visited her clinician with symptoms of cerebellar ataxia. Her brother was also found to have the disorder and the researchers asked if they, and their extended family, would take part in research to examine the genetic cause.

Blood samples were taken from two branches of the family and DNA, RNA and protein were extracted. The data was then analysed by the study research team. After looking at the entire genome, a rare variation in the DNA sequence of non-protein coding ribonucleic acid called RNU12 was found. This RNU12 variant was associated with affected family members, following the inheritance pattern expected of a recessive gene. 
Laboratory investigations confirmed that the variant impacts the expression and function of RNU12. This is an exciting finding, since most disease-associated mutations identified to date involve the small fraction of the genome that encodes proteins.
The study will open a new window for screening for cerebellar ataxia. It also shows geneticists how important it is to conduct research on all parts of the genome – both protein-coding and non-coding – when looking for causes of disease.

Annals of Neurology, January 2017, Mutation in noncoding RNA RNU12 causes early onset cerebellar ataxia, M. Elsaid et al., 10.1002/ana.24826

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