Studies involving younger patients with PSP have focused on familial cases with an identified single gene mutation despite the fact that PSP is considered to be a sporadic disease.11 Studies of autosomal‐dominant familial PSP phenotypes with variable disease durations and PSP‐type tau pathology at postmortem examination have identified MAPT and LRRK2 mutations.11 Of note, monogenic PSP mimics in younger patients include Perry syndrome (DCTN1 mutations) and Niemann‐Pick type C (NPC1/NPC2) mutations.11, 12. The gene discussed is MAPT; the disease is Down syndrome.