Novel presentation of AADC deficiency as a mild phenotype with exercise-induced dystonic crises: A case report.

Aromatic l-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive neurometabolic disorder caused by biallelic pathogenic variants in the DDC gene; approximately 140 patients have been described worldwide. AADC deficiency is characterised by a combined deficiency of dopamine, serotonin, adrenaline and noradrenaline causing a highly variable phenotype with developmental delay, early-onset hypotonia, movement disorders and autonomic symptoms. We expand the phenotype of this neurometabolic disorder by reporting on a paediatric patient with a mild phenotype with atypical exercise-induced dystonic crises, a feature that has not been described in AADC deficiency up till now. Additionally, we also present a second patient with typical characteristics and a severe phenotype. The diagnosis in both patients was confirmed by the presence of a homozygous pathogenic variant in the DDC gene and reduced AADC enzyme plasma activity. The use of whole exome sequencing-based strategies has played a crucial role in diagnosing these two patients.