What is Phenylketonuria?

What is Phenylketonuria?

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Phenylketonuria is an inherited metabolic disorder that causes mental disability. It was first described in 1934 by a Norwegian physician named Asbjörn Fölling (1888-1937) in two mentally disabled blond, blue-eyed brothers. The disease derives its name from a substance that is not normally found in the urine and is excreted in the urine. Phenylketonuria is an inherited metabolic disease. Children born with this disease cannot metabolize an amino acid called phenylalanine in protein foods. . In the first few months of life, infants with phenylketonuria cannot be distinguished from healthy infants. In children with untreated phenylketonuria, the decline in intelligence becomes apparent after the fifth and sixth months. Unlike their peers, they cannot acquire skills such as sitting, walking and speaking. Since their brain development is not normal, their heads remain small. Some children with phenylketonuria may have lighter hair and eyes than their parents.

Phenylketonuria is a familial disease. The parents of the child with phenylketonuria have two genes, one normal and one defective, responsible for the production of the phenylalanine hydroxylase enzyme. A child who receives defective genes from his parents is born with phenylketonuria. A child who receives a defective gene from his / her father carries the disease like his / her father, but does not show any disease. A child who receives intact genes from both of his parents is completely healthy. When parents are carriers, the probability of each child having phenylketonuria reaches as high as 25%.

Phenylketonuria is a disease that can be treated when diagnosed early. The general principle of treatment is to keep the level of phenylalanine in the blood within normal limits by reducing the amount of phenylalanine taken with food. Dietary therapy requires the use of special and pharmaceutical formulas and medicinal products, which are highly reduced or do not contain phenylalanine. Treatment should be performed very well during the first 8-10 years of life, at least with the fastest development of brain tissue. It is very important that the baby born with phenylketonuria is identified early without affecting the brain. There is a practical, economical test that can be applied to every newborn child developed for this purpose. In the first days of life, after feeding the baby for at least 24 hours, 2 drops of blood taken on a special filter paper is sufficient for diagnosis. When the sick baby is defined in the first days of life, it is imperative that all newborns should be screened for phenylketonuria in developed countries because appropriate mental treatment can prevent mental retardation. In addition, if the first child of the mother is born with a disease, it may be possible to determine whether the second baby is sick while the mother is still in the womb.

Individuals with phenylketonuria are characterized by the degree of mental disability that corresponds to the severity of the disease, as well as about 60% of patients characterized by light hair color, light eye color, and light skin color. Patients' body fluids, especially in the urine attracts a special smell. In patients with no treatment for phenylketonuria, it is inevitable to develop severe or very severe mental disability depending on the severity of the disease. Late diagnosed or poorly treated patients with phenylketonuria may experience hyperactivity, irritability, lack of attention, autistic behavior, food and toilet problems. There is no gender discrimination in the disease and it is observed with the same frequency in boys and girls.

A child with phenylketonuria diagnosed and treated successfully in the newborn period, like his peers, has the chance to start normal primary education, go to secondary and higher education, and have a profession by studying. Children diagnosed with delayed or poorly treated phenylketonuria receive special education for a long time and are prepared for the appropriate school. Children with phenylketonuria who can achieve normal education can be sent to primary schools within the framework of inclusive education. Children with phenylketonuria who cannot achieve normal education are referred to special education schools.
Hereditary metabolic diseases are rare. However, since there are many metabolic diseases, the number of children with metabolic diseases born annually is quite high. Almost all metabolic diseases, many of which cause mental disability, are inherited in an autosomal recessive way. If the mother and father are carriers, each child of this couple has a 25% chance of inherited hereditary diseases. Frequent consanguineous marriages in our country lead to a high frequency of autosomal recessive inherited metabolic diseases and hereditary metabolic diseases are an important cause of mental disability in our country. Clinical observations show that the prevalence of other metabolic diseases besides phenylketonuria, which is observed at a frequency of 1/4500 in our country, is higher than the world average values, although it is not known.

Phenylketonuria, an inherited metabolic disease, is still not well known in our society and causes many children to be disabled for life. Health institutions and physicians have a great duty to warn the families about this issue. It is possible to prevent this disease with a drop of blood.
Prepared: Erdi KANBAŞ - Special Education Specialist
For all kinds of opinions, suggestions and thoughts; I [email protected]


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- Trust, Star. Characteristics and Education of Mentally Retarded and Autistic Children, Marmara University. Special Education Department Istanbul: 2002.

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