Phenylketonuria (PKU disease) is an autosomal recessive genetic disorder which determines a deficiency in the enzyme named phenylalanine hydroxylase, necessary in the metabolism of phenylalanine. If phenylalanine hydroxylase is deficient, phenylalanine will accumulate and it will be converted into phenylpyruvate. The degree of enzyme deficiency, and as a consequence, the severity of the disease depends on the specific mutation and it varies among patients. At the moment, there is no cure for this disease, but some treatments are available.

The early diagnosis of the disease is very important and a genetic routine screening should be performed in every newborn , because at birth most newborns with the disease are clinically normal and do not display any . The clinical features of PKU disease will become obvious over several months as phenylalanine and phenylpyruvirate accumulates.

The typical sign of untreated PKU disease is severe mental retardation. Children also tend to be hyperactive and may develop a rash similar to infantile eczema. Albinism may occur due to the impaired synthesis of melanin (the pigment that gives the colour of the skin, eyes and hair) , but it may go unnoticed in the milder forms of the disease when the babies are considered to have blonde hair and blue eyes.

Other signs of nervous system function disturbances may be more subtle such as more active muscle tendon reflexes and an increased muscle toneor be more obvious such as seizures.

The untreated children may also have: microcephaly (smaller than normal head), proeminent zygomatic and maxilar bones, widely spaced teeth, poor development of tooth enamel, a delayed growth. With treatment and a good dietary control, the disease impact on the physical and mental development are minimized. Recent studies however indicate that the loss of dietary control during chilcdhood can have a great impact on cognitive development. These studies show that the people with PKU should maintain a strict dietary control throughout their lifetime. If development problems arise and dietary causes are suspected an intervention should be instituted as soon as possible

The excess of phenylacetic acid in perspiration leads to a specific odour of the babies diagnosed with the PKU disease. This smell has been described as musty or mousey.

The dermatological features of the disease are: an eczematoid skin rash, coarse skin and reduced pilosity. Other skin problems are represented by dry skin and severe itching.

The women with PKU disease who want to have a baby must to follow the PKU diet in order to avoid the high levels of phenilalanine which may affect the future physical and mental development of the fetus but they should also get enough nutrients to support the fetus.