Genetic testing may also be helpful, for example, a patient with childhood onset, non-progressive, spastic diplegia with no previous family history of HSP was long considered as affected by cerebral palsy, until his son also developed the same phenotype: genetic testing in these patients disclosed a heterozygous pathogenic variant in ATL1 (SPG3A) which had arisen de novo in the affected parent [75]. The gene discussed is ATL1; the disease is cerebral palsy.