Phenylketonuria (PKU) results in an inability to metabolize the amino acid phenylalanine to tryosine. If dietary phenylalanine is not metabolized, the amino acid accumulates to neurotoxic levels resulting. If untreated, the condition results in mental retardation, seizures, microcephaly and behavior abnormalities. PKU is among the disorders tested by newborn screening and treated by dietary restriction. The incidence of PKU is approximately 1 in 10,000 live births. PKU is autosomal recessive disorder and caused by mutations in the PAH gene (12q22-q24) leading to deficiency of phenylalanine hydroxylase. Disease severity, clinical phenotype, and effectiveness of treatment differs among the different PAH mutations and correlates with the level of PAH enzyme activity. Complete or near complete absence of enzyme activity results in classical phenylketouria (PKU), which requires strict dietary restraint of phenylalanine for life. Milder enzyme deficiencies can result in non-PKU hyperphenylalaninemia (non-PKU HPA) or variant PKU. Carriers of PKU are unaffected.
This test is indicated for:
- Patients with a biochemical diagnosis of PKU.
- Individuals with biochemical test results indicating carrier status of PKU.
- Individuals who are at risk to be carriers of PKU, when the proband is unavailable for testing.
Sequencing is not appropriate for prenatal samples in which familial mutations have not been identified.
DNA isolated from peripheral blood is hybridized to a CGH array to detect deletions and duplications. The targeted CGH array has overlapping probes which cover the entire genomic region.
Detection is limited to duplications and deletions. Array CGH will not detect point mutations or intronic mutations. Results of molecular analysis must be interpreted in the context of the patient's clinical and/or biochemical phenotype.
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
- Organic Acid Analysis (OA) and Plasma Amino Acid (AA) Analysis are used in the diagnoses of a patient with PKU.
- Prenatal testing is available to couples who are confirmed carriers of mutations. Please contact the laboratory genetic counselor to discuss appropriate testing prior to collecting a prenatal specimen.