6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is a rare disorder that results in the lack of a molecule called tetrahydrobiopterin (BH4). Lack of BH4 results in high levels of an amino acid called phenylalanine, a condition known as hyperphenylalaninemia. Phenylalanine and other amino acids are building blocks for proteins and are essential for proper growth and development. Additionally, BH4 deficiency results in very low levels of chemicals which transmit impulses from one nerve cell to another (neurotransmitters). Individuals with PTPS deficiency can have a variety of symptoms including neurological abnormalities (seizures and swallowing problems), low muscle tone (hypotonia) in the body, excess muscle tone (rigidity) in the arms and legs, loss of coordination or delayed motor development, delayed intellectual development, and temperature regulation problems. Infants with PTPS deficiency are often healthy at birth but quickly begin to show signs of failure to thrive. Additional symptoms generally appear within the first four to six months of life. A small head size (microcephaly) may also be identified in early infancy.
The symptoms of PTPS deficiency can vary widely and range from mild to severe. Twenty percent of individuals have the mild or atypical form. Individuals with the mild or atypical form of PTPS deficiency have moderate or transient alterations in phenylalanine levels and normal levels of neurotransmitters.
PTPS deficiency is a rare disorder. In Caucasians, PTPS deficiency occurs in about 1 in 1,000,000 individuals, but is more frequent in East Asian populations.
Treatment of PTPS deficiency will generally focus on reducing the high phenylalanine levels by dietary intervention and normalizing the neurotransmitter levels. Treatment may include synthetic BH4 and other medications which help restore neurotransmitter levels. Patients with the severe form may need both synthetic BH4 supplementation and medications to restore neurotransmitters, while mild cases will need only BH4 supplementation.
Prompt diagnosis and early treatment of PTPS deficiency is critical for reducing or preventing potentially severe, irreversible neurologic damage. Without early diagnosis and treatment, this condition is potentially life-limiting.
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