Abstracts

Rationale: Typically SSADH deficiency, a defect of GABA metabolism, manifests as a relatively nonprogressive encephalopathy with a median age of diagnosis of two years. The oldest previously reported patient at age of diagnosis was 25 years. Seizure onset is often in adolescence and is reported overall in just < 50% of the patient population. Methods: A 63-year-old man with longstanding intellectual disability was diagnosed with SSADH deficiency following hospitalization for progressive decline, escalating convulsions, and prolonged periods of altered consciousness. We reviewed our SSADH database adult cohort to derive natural history information. Results: Of 102 patients in the database, there are 35 individuals age 18+ years (stratification: 24 patients aged 18 to 29 years, 9 in the thirties, one age 45, and the index case, now deceased at age 63). Only three of the 102 patients were diagnosed after 18 years old. Of the 35 adults, 22 (63%) have epilepsy. Predominant seizure types are generalized tonic-clonic, absence, and myoclonic. EEGs in adulthood were normal in 40%, showed background slowing or disorganization in 35%, and interictal epileptiform discharges in 30%. Psychiatric symptoms were prominent with anxiety, sleep disturbances, and severe obsessive-compulsive disorder. Hyperactive behaviour was described at some time in their history in 80%. SUDEP is reported and epilepsy appears to become more intractable with age. Conclusions: We identified 35 SSADH patients in our database over age 18 years of age following diagnosis of the first reported case over age 45. The illness had a progressive course with escalating seizures in the index case with fatality at age 63. Epilepsy is more common in the adult than pediatric SSADH cohort; SUDEP and increasing seizure intractability with age are reported.