Researchers do not know the exact prevalence (the frequency of disease in a population) of aromatic l-amino acid decarboxylase (AADC) deficiency. However, they conducted several studies to try to estimate it. These studies have detected the disease in several countries around the world.
AADC Deficiency Prevalence Estimates
AADC deficiency remains a very rare disease with only 100 people documented in the medical literature.
Several studies have attempted to estimate the prevalence of the disease. A study screened 127,987 newborns in Taiwan from September 2013 to December 2015 and found four cases of AADC deficiency. These cases have resulted in a birth prevalence rate of AADC of one in 32,000 babies. Researchers know there is a founding mutation among the people of Taiwan. A founder mutation occurs when a person with a certain mutation becomes one of the initial founders of a new population in an isolated setting, such as Taiwan.
Of the four children with AADC deficiency, three had two copies of the founder mutation. The fourth had one copy with a new mutation in the other copy of the gene. The study also looked at the prevalence carriers of this mutation (those who have one mutated and one functional copy of the gene) and found it to be one of 146 copies.
A projection study of patients in Hong Kong analyzed samples from 845 patients and identified two cases of AADC deficiency. The finding suggests that the condition may be the cause of about 0.24% of cases of undiagnosed neurological disorders.
In the United States, the European Union, and Japan, researchers reported a 2016 population prevalence (the number of cases in the total population) of AADC deficiency of 840, 853 and 125, respectively, indicating the differences between countries.
A study focused on patients in the United States studied the prevalence of mutations causing AADC deficiency in samples from 19,684 patients with unknown neurological disorders. The study found that 36 patients tested positive for mutations related to AADC deficiency. This result suggests that approximately 0.18% of unknown neurologic cases may be AADC deficiency.
Factors Affecting Estimates
There are a number of factors that could affect the estimated prevalence of AADC deficiency. There may be differences in populations depending on location and heritage, as in the case of the founder effect in the Taiwanese population.
AADC deficiency remains an often undiagnosed or misdiagnosed disease. In reality, the average age of symptom development is 2.7 months, while the average age of diagnosis is 3.5 years.
The reason why it is so difficult to diagnose AADC is that its symptoms are very similar to those of several other diseases, such as epilepsy, cerebral palsy, neuromuscular weakness, and mitochondrial disease. Due to the overlap in symptoms and the rarity of AADC deficiency, many cases can be misdiagnosed, which can also reduce the number of cases.
Last updated: October 21, 2020
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