Phillip Pearl, MD, and Keith Hyland, PhD, give an overview of AADC deficiency
Pearl: AADC deficiency is an ultra-rare neurotransmitter disease of childhood. AADC is an acronym for an enzyme known as aromatic amino acid decarboxylase.
Aromatic amino acid decarboxylase is the enzyme that converts L-dopa to dopamine and 5-hydroxytryptophan to 5-hydroxytryptamine, which is serotonin.
Hyland: AADC deficiency is an inherited disorder. It affects 2 major neurotransmitter systems within the central and peripheral nervous systems. It’s a lack of a particular enzyme that’s required for the synthesis of dopamine, which controls movement, serotonin, which controls mood and such like things, and also norepinephrine and adrenaline, which are autonomic nervous system neurotransmitters.
When you lack AADC or the enzyme, which is actually aromatic L-amino acid decarboxylase and we abbreviate it to AADC because it’s much easier. When you lack that, obviously you lack those neurotransmitters and you have drastic neurological consequences because of that.
Pearl: AADC deficiency is a genetic disorder. It’s caused by having mutations of the gene DDC that encodes for the AADC enzyme. It’s inherited autosomal recessively, which means a child inherits 2 abnormal variants of that DDC gene.
It is predominantly thought of as a movement disorder, but the truth is it is far more than a movement disorder. It’s a disorder that affects tone, typically causes severe hypotonia in the beginning, can cause some hypertonia too, but mainly low tone, causes developmental delay across the board.
The long-term impact tends to be very severe, limitations in longevity, life expectancy, and severe deficits.
The classical case will present typically at 2 or 3 months of age, although the diagnosis is not often made until 2 or 3 years of age. But typically, it’ll present at 2 to 3 months, although I’ve seen it present in the neonatal period.