PO099 Autosomal dominant gene negative frontotemporal dementia-think sca17

SCA 17 is a rare, autosomal dominant ataxia caused by CAG/CAA repeat expansion in TBP gene. Dementia can occur. Parkinsonism, chorea, dystonia and pyramidal signs may occur. We report an Irish family with autosomal dominant partially penetrant frontal dementia with cerebellar atrophy due to SCA17. A 44-year-old doctor presented with 18–month history of behavioural problems. She slowed down, became apathetic and more irritable. One sister developed personality change at age 45 with apathy, poor memory; another sister at age 39 became dysarthric and unsteady. Her brother at age 52 laughed inappropriately, was dysarthric and unsteady. Mother age 73 had an arthritic antalgic gait. Father was jocular and disinhibited. The proband’s MRI brain showed cerebellar atrophy and FDG-PET:cerebellar hypometabolism. C9orf72 was negative and MAPT testing detected exon 9 c.726C>T variant in the proband. Subsequent testing on 9 siblings and both parents failed to show co-segregation with dementia. SCA17 testing revealed a TBP gene 43 repeat expansion in all affected siblings and in the ‘unaffected’ mother. The cognitive impairement in SCA17 is consistent with FTD. In familial FTD SCA17 should be considered if cerebellar atrophy is present. Segregation analysis is crucial. MAPT variant (c.726C>T exon 9) is a polymorphism.