PT - JOURNAL ARTICLE AU - Ana Luísa Rocha AU - Andreia Costa AU - Maria Carolina Garrett AU - Joana Meireles TI - Difficult case of a rare form of familial Alzheimer’s disease with PSEN1 P117L mutation AID - 10.1136/bcr-2018-226664 DP - 2018 Nov 01 TA - BMJ Case Reports PG - e226664 VI - 11 IP - 1 4099 - http://casereports.bmj.com/content/11/1/e226664.short 4100 - http://casereports.bmj.com/content/11/1/e226664.full SO - BMJ Case Reports2018 Nov 01; 11 AB - Less than 10% of Alzheimer’s disease (AD) cases are familial. Presenilin-1 (PSEN1) mutations are the most frequent aetiology and may be associated to atypical neurological manifestations. We report the case of a 27-year-old right-handed man, ensuing with mild cognitive impairment, motor discoordination and axial myoclonus after a parachute accident. At age 32 he was referred to our neurology clinic, presenting cognitive impairment, cerebellar syndrome, axial myoclonus and hypomimia, without other signs of parkinsonism. Because of absence of family history, he was worked up along the line of spinal ataxic disorders. Later, he developed pseudobulbar affect, cognitive deterioration, right upper limb paresis and spastic paraparesis. Subsequent investigation identified a PSEN1 P117L mutation and the diagnosis of autosomal dominant AD was made. This case illustrates the diagnostic challenge imposed by atypical presentation of de novo PSEN1 mutation, leading to unnecessary investigation. Genetic study might be essential for defining the diagnosis.