Phenylketonuria (PKU) cases have been reported to different degrees in countries across the world. There have been a number of studies to estimate its prevalence, or how common the disease is in a particular population at a given period of time. However, the results have varied considerably from country to country.
Estimates of PKU prevalence
Several studies have looked at the prevalence of PKU in specific countries over the years. Two recent studies analyzed the literature and found differing values for PKU’s prevalence both globally and in several specific countries.
The first review looked at 53 studies that included a total of 119,152,905 people and spanned from 1964 to 2017. Of those studies, 46 met the criteria that the researchers used to calculate a global estimate of PKU prevalence. According to this estimate, the worldwide prevalence of PKU is around six people per 100,000 births. The estimates for different countries ranged from a high of just above 38 people per 100,000 in Turkey to a low of 0.3 per 100,000 in Thailand.
The second analysis involved 256 articles published between January 1980 and October 2019. From those articles, the scientists identified 16,092 individuals from 51 countries and used them to calculate a global prevalence of one in 23,930 live births – or about 4.18 per 100,000. The researchers found that the highest prevalence was in Italy (one in 4,500 births) and the lowest was in Japan (one in 125,000 births).
While the two studies did not agree on exact prevalence, they both did note a trend that showed that the highest PKU prevalence was in Europe and around the Mediterranean and the lowest was in Southeast Asian countries.
Factors affecting different estimates of prevalence
The two studies had differing estimates of the prevalence of PKU both globally and per country.
One possible cause for the difference is the time period that the studies covered. Earlier diagnostic techniques might not have been as sensitive or accurate as those used more recently. The first study analyzed a slightly earlier and longer time period that spanned over 50 years. While the second was a couple of years more recent, it did not quite cover a 40-year time period.
The second analysis also combined patients with classic PKU, mild PKU, and mild hyperphenylalaninemia, or individuals with high levels of phenylalanine in the blood. This would affect the numbers as compared with the first study, which only investigated classic PKU.
There also are factors that could affect the estimates for specific studies in different countries. One such factor is the difference in the rate of consanguineous marriage, which is a union between two individuals who are related as second cousins or closer. A child has PKU when they inherit a mutated copy of the disease-causing gene from each parent. If the parents are closely related, and PKU runs in the family, there is a higher chance that both are carriers of the disease and each has one faulty copy of the gene.
Another factor that could affect the estimates for individual countries is the sample size. The larger the number of people that are screened, the more accurate the results will be.
Importance of newborn screening
A large number of countries adopted newborn screening for PKU, in which infants are tested for the disorder in the first days of life. This test, which involves collecting a few drops of blood, usually from the baby’s heel, has been an integral part of the ability to estimate the prevalence of PKU across different countries. However, not all countries require such screening, which can limit the data.
Last updated: Dec. 17, 2020
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