Case report: discovery of 2 gene variants for aromatic L-amino acid decarboxylase deficiency in 2 African American siblings

BACKGROUND: Aromatic l-amino acid decarboxylase (AADC) deficiency is a rare genetic disorder with heterogeneous phenotypic spectrum resulting from disease-causing variants in the dopa decarboxylase (DDC) gene. Consensus guidelines recommend dopamine agonists, monoamine oxidase inhibitors, and other symptomatic treatments, but most patients have an unrelenting disease course with no response to these therapies. CASE PRESENTATION: We describe 2 African American siblings with AADC deficiency and identify 2 DDC gene variants not previously associated with the disorder. The patients were evaluated for cognitive and neurologic impairments. Diagnosis of AADC deficiency was initially based on evaluation of urine and plasma metabolites, followed by targeted DDC gene sequencing. The first patient, a firstborn African American female, had moderate elevations of vanillactic and vanilpyruvic acids, and slight elevation of N-acetylvanilalanine in urine. The second patient, an African American female and younger sibling of the first patient, had low AADC enzyme activity and elevated 3-O-methyldopa levels in plasma. Genetic testing confirmed that both siblings possessed the same 2 DDC gene variants, which were identified as NM_000790.3: c.48C > A (p.Tyr16Ter) and NM_000790.3: c.116G > C (p.Arg39Pro). CONCLUSIONS: This report describes 2 previously unknown patients with AADC deficiency and confirmed the presence of 2 DDC gene variants not previously associated with this disorder. Further research is needed to identify disease-modifying treatments for this devastating neurometabolic disorder. Gene therapy with a recombinant adeno-associated viral vector serotype 2 carrying the gene for the human AADC protein (AAV2-hAADC) is currently in clinical development.