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Succinic semialdehyde dehydrogenase deficiency

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    My patient was the daughter of Pakistani parents. She presented with typical features of subacute sclerosing panenecephalitis (SSPE) and the diagnosis was confirmed by a high cerebrospinal fluid measles antibody titre. She had had mild to moderate learning difficulties before the onset of SSPE and a younger brother presented later with developmental slowness and was shown to have succinic semialdehyde dehydrogenase (SSADH) deficiency. Testing of the girl at that time showed that she also had SSADH deficiency as well as SSPE.  A report from several centres in the USA and north west Europe (K Michael Gibson and colleagues, Pediatrics1997;99:567-74) has added 23 patients with SSADH deficiency to the previously reported total of about 40. Only seven of the 23 were of American-European or western European origin; four were Turkish, three Indian, two Korean, two Lebanese, and one each Syrian, Saudi, Pakistani, Chinese, and Greenland Inuit. Motor, intellectual, or language delay and hypotonia were each present in about three quarters of the patients. Eleven patients were thought to have had seizures but they were a mixed bag of seizure types often non-recurrent and in several cases dubious. Only in three Indian siblings did epilepsy represent a major problem. Ataxia, behaviour problems, and hyperactivity each affected 30% of patients.  SSADH deficiency affects GABA (gamma aminobutyric acid) metabolism with accumulation of 4-hydroxybutyric acid. Treatment with vigabatrin has been suggested but it appeared beneficial in only 35% in this series. High doses of vigabatrin seemed harmful in one patient who responded well to lower dosage.  The diagnosis depends on urine organic acid analysis showing 4-hydroxybutyric aciduria. This group suggests doing such analysis for any patient presenting with two or more of the four main features—intellectual, motor, or language delay, and unexplained hypotonia.