Epidemiological aspects in phenylketonuria patients from a region in northwestern Romania

Introduction. Phenylketonuria (PKU), a genetic disease with autosomal dominant transmission, is the most frequent inborn error in aminoacidic metabolism. The variations in phenylalanine-hydroxylase (PAH) gene lead to a lowered enzymatic activity causing hyperphenylalaninemia. PKU has a mean European prevalence of 1:10,000 newborns, with a large variation in different ethnicities and geographic regions. The large genetic variability (over 1200 genetic variants known) as well as other factors determines a wide spectrum of metabolic phenotypes. Untreated, PKU leads to irreversible intellectual disability, low stature, hypopigmentation, motor deficits, seizures, but the early diagnosis and treatment enables almost normal somatic and mental development. Aim. The aim of this study is the determination of the impact of non-genetic factors over the clinical phenotype of PKU patients in a region of north-west Romania. Material and method. The study group is formed from 44 patients diagnosed with phenylketonuria in the 1981 – 2021 period, found in the database of Bihor Regional Center for Medical Genetics, Emergency Clinical County Hospital, Oradea, Romania. The collected data was referring to the age, sex and domicile of the patients, the age of the diagnosis and the beginning of the treatment, also the metabolic control over the years, the metabolic phenotype of the patients and its impact on the clinical phenotype (IQ, the presence or absence of intellectual disability or the existence of a specific clinical phenotype). Results. The majority of patients (66%) were diagnosticated with phenylketonuria in the first 4 months of life, although there were cases with a late diagnosis, 20.5% of the patients were diagnosticated after the age of 1 year. Based on the pre-treatment plasmatic levels of phenylalanine, the majority of cases (72.7%) had a severe metabolic phenotype (classic PKU - cPKU), 20.5% of cases had a milder form of PKU (mPKU) and 6.8% of patients were found with a mild hyperphenylalaninemia (HPA). In the case of 23 patients, an optimal metabolic control was not obtained. The specific phenotype (blonde hair, light skin, blue eyes) was found in 22.7% of cases, 77.3% not having these features. At 68.2% of cases intellectual disability was found, with different levels of severity: 5 patients (11.5%) had liminal intellect, 9 patients (20.5%) had mild mental retardation, 6 patients (13.6%) had moderate mental retardation, 9 cases (20.5%) were with severe mental retardation and 1 patient (2.3%) had profound mental retardation; 31.8% of cases had normal intellect. The prevalence in Bihor county is 1:7,843 newborns. Discussions. A partial or, in rare cases, total lack of dietetic treatment was observed in all patients over 20 years old (current age). The delay in treatment initiation or an insufficient treatment, with a suboptimal metabolic control, will affect patient’s intellect, regardless of metabolic phenotype. If in 20 years old patients, or older, the main reason for mental retardation is the lack of dietetic treatment availability in the first years of life, for the younger patients the reason for mental retardation is usually a lack of compliance with the treatment. The majority of metabolic phenotypes is cPKU, in concordance with the literature data; the mild phenotype (HPA) was observed in a small percentage of patients, smaller than the data reported in the literature. In the first two studied decades the mild phenotypes were seldom observed. In the absence of screening tests or suggestive clinical manifestation it can be assumed that HPA patients remained undiagnosed, which would explain the small HPA percentage in the study group. A significant improvement in metabolic control in younger patients compared with older ones was observed, which denotes a better access to specific alimentation on one side, and o the other side, a better understanding of the disease from the patients and their families. Also, this study confirms a known fact that the diet in PKU is of great importance in the disease evolution. In this study there were included patients with severe metabolic phenotype with good metabolic control which reached adulthood without intellectual deficits, with higher education, social integrated and also patients with mild metabolic phenotype but with a poor metabolic control which developed intellectual deficiency. Conclusions. The PKU prevalence in Bihor county is higher than the estimated national value. The late diagnosis and treatment or the poor metabolic control led to intellectual disability, regardless of the metabolic phenotype. PKU screening and the better access to treatment allows younger generations of patients to enjoy a superior quality of life than the patients from the first two studied decades.