What does pku negative mean?

PKU refers to the screening for phenylketonuria, an enzyme that, if defective, often has an adverse effect on the growth and development of the child. If it is negative, it means that the child does not have this disease and there is no need to worry. Phenylketonuria is an amino acid metabolism disease, which refers to a defect in the enzyme in the phenylalanine metabolic pathway. It often leads to developmental delay in children, neurological and mental abnormalities in children, and sometimes abnormalities in the children's skin and hair.

What is phenylketonuria

Phenylketonuria (PKU) is a common amino acid metabolic disease caused by an enzyme defect in the phenylalanine (PA) metabolic pathway, which prevents phenylalanine from being converted into tyrosine, leading to the accumulation of phenylalanine and its ketoacids, which are excreted in large quantities in the urine.

This disease is relatively common among hereditary amino acid metabolism deficiency diseases, and its inheritance pattern is autosomal recessive. The clinical manifestations are heterogeneous, and the main clinical features are mental retardation, neuropsychiatric symptoms, eczema, skin scratch signs, depigmentation, rat odor, and abnormal electroencephalogram. If early diagnosis and early treatment are available, the aforementioned clinical manifestations may not occur, intelligence may return to normal, and EEG abnormalities may also be restored.

Clinical manifestations 1. Growth and development retardation In addition to physical growth and development retardation, the main manifestation is intellectual retardation. It is manifested in an IQ lower than that of normal children of the same age, and it can appear 4 to 9 months after birth. In severe cases, the IQ is below 50, and language development disorders are particularly obvious. These manifestations indicate brain development disorders. 2. Neuropsychiatric manifestations include cerebellar malformation due to brain atrophy and recurrent convulsions, which tend to improve with age. Increased muscle tone and hyperreflexia. There is often restlessness, hyperactivity and abnormal behavior. 3. Skin and hair manifestations: The skin is often dry and prone to eczema and skin scratches. Because tyrosinase is inhibited, melanin synthesis is reduced, so the hair of the affected child is light brown. 4. Others Due to the lack of phenylalanine hydroxylase, phenylalanine produces increased phenyllactic acid and phenylacetic acid from another pathway, which are excreted in sweat and urine and have a musty odor (or mouse odor).

Cause: Phenylalanine is one of the essential amino acids for the human body. The normal daily intake required by a normal person is about 200 to 500 mg, of which 1/3 is used for protein synthesis, and 2/3 is converted into tyrosine through phenylalanine hydroxylase (PAH) in liver cells to synthesize thyroxine, adrenaline and melanin.

In the process of converting phenylalanine into tyrosine, in addition to PAH, tetrahydrobiopterin (BH4) must also participate as a coenzyme. Gene mutations may cause defects in the activity of related enzymes, resulting in abnormal accumulation of phenylalanine.