Background. Phenylketonuria (PKU) and biotinidase deficiency (BD) are autosomal recessive diseases. If they are not identified and treated early, severe intellectual disability and developmental delay occur. This study was conducted to calculate the ten-year incidence of PKU and BD in the Diyarbakır province of Turkey.

Methods. This cross-sectional study included patients born between 2011-2020 and diagnosed with PKU and BD. Patients with a clear diagnosis had their records evaluated retrospectively.

Results. Between 2011 and 2020, blood was taken from 417,525 newborns` heels in Diyarbakir province. As a result of further diagnostic testing, 53 PKU (Incidence: 1:7878) and 177 BD (Incidence: 1:2359) were detected. Of the patients with BD, 56% had profound BD and 44% had partial BD. The records of a total of 269 patients (PKU: 25; BD: 123; Hyperphenylalaninemia: 121) were examined. Parents of 65% (n=15) of the patients diagnosed with PKU and 46.6% (n=55) of the patients diagnosed with BD were consanguineous.

Conclusions. The incidence of both PKU and BD was found to be high in our region. The high number of consanguineous marriages was regarded as the most important explanation for the high frequency of these illnesses.

Keywords: biotinidase deficiency, incidence, newborn screening, phenylketonuria