Novel Variants in Aromatic L-amino Acid Decarboxylase Deficiency: Case Report of Sisters with Mild Phenotype

Background: Aromatic L-amino acid decarboxylase (AADC) deficiency, caused by a pathogenic variant in the dopa decarboxylase (DDC) gene, is a rare neurometabolic disorder in which catecholamine and serotonin are not synthesized. From a large number of reports, it has been recognized that most affected patients show severe developmental delay in a bedridden state and are unable to speak. On the other hand, patients with a mild phenotype with AADC deficiency have been reported, but they number only a few cases. Therefore, the variation of phenotypes of the disease appears to be broad, and it may be challenging to diagnose an atypical phenotype as AADC deficiency.

Case Report: We report novel compound heterozygous variants in DDC (c.202G > A and c.254C > T) in two sisters, whose main complaint was mild developmental delay, by whole-exome sequencing (WES). Additionally, we describe their clinical features and provide an image that shows the variants located at different sites responsible for the catalysis of AADC in a three-dimensional structure. The patients were prescribed a Monoamine oxidase (MAO) inhibitor after diagnosis.

Interpretation: Our cases indicate that a comprehensive genomic approach helps to diagnose AADC deficiency with atypical features, and underscore the significance of understanding the variations of this disorder for diagnosis and appropriate treatment.