Succinic semialdehyde dehydrogenase deficiency

Succinic semialdehyde dehydrogenase (SSADH) deficiency, also known as 4-hydroxybutyric aciduria or gamma-hydroxybutyric aciduria, is a rare inherited disorder of gamma-aminobutyric acid (GABA) metabolism. It is caused by pathogenic variants in the ALDH5A1 gene, which encodes the mitochondrial enzyme succinic semialdehyde dehydrogenase. This enzyme is responsible for the oxidation of succinic semialdehyde to succinic acid in the GABA degradation pathway. When the enzyme is deficient, succinic semialdehyde accumulates and is converted to gamma-hydroxybutyric acid (GHB), which builds up in the blood, urine, and cerebrospinal fluid. The disease primarily affects the central nervous system. Clinical features are variable but typically include developmental delay, intellectual disability, hypotonia, speech and language impairment, and expressive language difficulties. Neuropsychiatric manifestations are common and may include attention deficit, anxiety, obsessive-compulsive behaviors, autistic-like features, and sleep disturbances. Approximately half of affected individuals develop seizures, which can be of various types including generalized tonic-clonic and absence seizures. Ataxia and movement disorders such as choreoathetosis and dystonia may also occur. Brain MRI frequently shows abnormalities in the globus pallidus, cerebellar dentate nucleus, and subcortical white matter, with increased T2 signal intensity. There is currently no specific curative treatment for SSADH deficiency. Management is primarily supportive and symptomatic, including antiepileptic medications for seizure control, physical therapy, occupational therapy, and speech therapy. Vigabatrin, an irreversible inhibitor of GABA transaminase, has been used in some patients with variable results, as it may reduce GHB levels but can also increase GABA levels. Clinical trials investigating novel therapeutic approaches, including mTOR inhibitors and other targeted therapies, are ongoing. Prognosis is variable, with some individuals achieving a degree of independence while others require lifelong support.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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