Aromatic L-Amino Acid Decarboxylase Deficiency

Aromatic L-amino acid decarboxylase deficiency was reported in 1990 in one family (male twins).

Disorders of Neurotransmitters Diseases

Clinical Presentation Aromatic L-Amino Acid Decarboxylase Deficiency

Generalized hypotonia, developmental delay, and paroxysmal movements with oculogyric crises were noted at 2 months of age. At 9 months there was also a fine chorea of the distal limbs and temperature instability with excessive sweating. The electroencephalogram (EEG) was normal, but brain imaging showed cerebral atrophy.

Disorders of Neurotransmitters Diseases

Metabolic Derangement Aromatic L-Amino Acid Decarboxylase Deficiency

Deficiency of aromatic L-amino acid decarboxylase leads to accumulation of L-dopa, its metabolite 3-methoxytyrosine, and of 5-hydroxytryptophan in CSF, plasma, and urine, as L-amino acid decarboxylase has both L-dopa decarboxylase and 5- hydroxytryptophan decarboxylase activities. In urine, there is also a gross elevation of vanillactic acid, a metabolite of 3-methoxytyrosine.

On the other hand, blood concentrations of serotonin and catecholamines, and CSF concentrations of their metabolites 5-hydroxyindoleacetic acid and homovanillic acid, are decreased. Very low activity of L-dopa decarboxylase in plasma and
of 5-hydroxytryptophan decarboxylase in
a liver biopsy sample confirmed the diagnosis. The parents of the affected index patient had plasma aromatic L-amino acid decarboxylase activity of 16% and 19% of control values, respectively, and yet they had a totally normal phenotype.

Disorders of Neurotransmitters Diseases

Diagnostic Tests Aromatic L-Amino Acid Decarboxylase Deficiency

The diagnosis can be made by finding the characteristic profile in CSF or very high levels of 3-methoxytyrosine and very low levels of 5-hydroxyindoleacetic acid and homovanillic acid. This suggests a systematic investigation of monoamine metabolism in unexplained neurological disease. Very low activity of aromatic L-amino acid decarboxylase in plasma and/or liver tissue confirms the diagnosis. The feasibility of prenatal diagnosis is not yet known.

Disorders of Neurotransmitters Diseases

Treatment and Prognosis Aromatic L-Amino Acid Decarboxylase Deficiency

The index patients were treated with pyridoxine (cofactor of the defective enzyme), bromocriptine (dopamine agonist), and tranylcypromine (monoamine oxidase inhibitor). Pyridoxine (50 mg b.d) caused a drop in CSF 3-methoxytyrosine and L-dopa and an increase in homovanillic acid. However, there was no clinical effect. Bromocripine alone stopped the oculogyric crises, while tranylcypromine improved muscle tone, increased spontaneous movements, and reduced sweating. Growth, which had stopped, resumed during treatment. Anti convulsants were ineffective.

Disorders of Neurotransmitters Diseases

Genetics Aromatic L-Amino Acid Decarboxylase Deficiency

Inheritance is most probably autosomal recessive.

Disorders of Neurotransmitters Diseases