In some patients who present with Parkinson disease at a young age, with or without a family history, there will be an underlying genetic cause.

Ataxia telangiectasia is a rare autosomal recessive DNA repair disorder caused by pathogenic variants in the ATM gene. Clinical features include immunodeficiency, impaired growth and cancer susceptibility, as well as the characteristic cerebellar ataxia and scleral telangiectasias.