Biopterin defect in cofactor biosynthesis

GTP cyclohydrolase I deficiency


Type of disease: Rare conditions

Biopterin defect in cofactor biosynthesis (BIOPT-BS) is a rare genetic disorder causing high levels of the amino acid phenylalanine. Our body breaks down extra protein we eat into its building blocks, the amino acids. Special proteins breakdown any extra amino acids into harmless products our body can get rid of. If a protein needed to break down phenylalanine is missing, phenylalanine builds up. Symptoms include seizures (epilepsy), muscle weakness (hypotonia), and trouble regulating body temperature. A person with BIOPT-BS also has trouble making chemical signals for the nervous system (neurotransmitters). A lack of neurotransmitters can cause developmental delays, sleep disorders, and behavioral problems.

BIOPT-BS is caused by a mutation (change) to the PTS or GCH1 genes. Both of these genes make proteins which help make tetrahydrobiopterin (BH4). BH4 helps break down phenylalanine, so if there isn’t enough BH4, phenylalanine builds up. BHR also makes neurotransmitters. A baby with BIOPT-BS appears healthy until the level of phenylalanine gets too high, usually around 4 months.

BIOPT-BS is an autosomal recessive disorder, meaning both copies of either PTS or GCH1 genes must be changed to have symptoms. High levels of phenylalanine in the blood may suggest BIOPT-BS. Other genetic disorders also cause high levels, so genetic testing is needed to confirm the diagnosis. Treatment for BIOPT-BS includes supplements to increase BH4 levels. Many babies are screened for BIOPT-BS at birth so treatment can begin early, but newborn screening conditions vary by state. For more information, visit Baby’s First Test. Talk with your baby’s doctor about the most current treatment options. Genetic counselors and support groups are also good sources of information.

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