Diagnostic Challenges and Outcome of Classical Phenylketonuria in a Resource‐Constrained Middle Eastern Country

<b>Background:</b> Scarce data on classical phenylketonuria diagnosis and outcome in low-income Middle Eastern countries is available. The effect of phenylketonuria diet on growth parameters is still controversial. This 15-year retrospective study is aimed at examining the diagnosis, outcome, and growth of classical phenylketonuria patients following a phenylalanine-restricted Mediterranean diet in Lebanon. <b>Methods:</b> A retrospective review of the charts of patients diagnosed and followed between 2008 and 2023 at the American University of Beirut Medical Center, Lebanon, was conducted. Age at diagnosis, molecular profile, neurological status, anthropometric measurements, diet, and metabolic control were analyzed. <b>Results:</b> Out of 82 patients, 35 met the inclusion criteria. The majority were late-diagnosed (average age: 4 years) with poor neurological outcome. The Mediterranean variant IVS10-11G>A in a homozygous state was identified in 63%. There was no statistically significant difference between body mass index or height for age <i>z</i>-scores at first and last encounter for all patients on phenylalanine-restricted Mediterranean diet. <b>Conclusions:</b> Phenylalanine-restricted Mediterranean diet seems to preserve growth parameters in classical phenylketonuria patients. However, achieving a neurotypical outcome remains challenging in the absence of systematic newborn screening in Lebanon, a resource-constrained country with high rates of consanguinity.