Genetic drift and founder effect may have also played a role in the mutation spectrum we observed. The data obtained in our study can also be used in the development of genetic tests for phenylketonuria. This study was conducted in the patients diagnosed with phenylketonuria who presented to Scientific Research Pediatric Institute of the Ministry of Health of Azerbaijan and hospitals of different regions of Azerbaijan The present study aimed to determine frequencies of mutations in the phenylalanine hydroxylase gene (PAH) in 30 patients diagnosed with phenylketonuria, from 633 person who presented to Scientific Research Pediatric Institute of the Ministry of Health of Azerbaijan and hospitals of different regions of Azerbaijan over the period from 2016 to 2022. Molecular genetic methods for detecting mutations are based on differences in the DNA sequence. More than 600 mutations in the PAH gene in exons 6, 7, 8, 11 and 12 have been detected in various countries around the world. Among them, 18 different mutations were found in Azerbaijani patients (V245V, R261Q, Q232Q, V245V, P281L, R241C, L385L, V399V, E280K, R261X, A434D, R176X, Ex6-96A> G, R241C, R243Q, R256Q). Nutritional therapy and adaptation to this treatment are essential in PKU, a congenital metabolic disease. This study was undertaken to determine the contribution of families in coping with problems that make nutritional adaptation difficult. Difficulties faced by families in achieving low-protein, low-phenylalanine-containing products that are inadequate and expensive to achieve proper nutrition in PKU disease, the ways to cope with these difficulties, the problems that can be or are experienced in harmony with the environment of the patients, and the ways to cope with them consists the subject of the study. Phenylketonuria (PKU) is an autosomal recessive genetic disease, caused by the phenylalanine hydroxylase (PAH) deficiency in the metabolic pathway, which prevents phenylalanine from being converted into tyrosine, leading to a large amount of phenylalanine discharged from the urine. Therefore, it is necessary to establish a simple, fast, accurate and reliable PKU molecular diagnostic method for clinical diagnosis. As a result of the study it is understood that it is necessary and important to educate the families, to prevent the marriage of the relatives and to raise the awareness of the community in order not to increase the prevalence of recessive diseases in general frame. In the private area, the support of the family, the care to be shown about the nutrition, the minimization of the negative effects of the environment, the self-confidence to be given to the patient can create cognitive health and a life without any problems.