Phenylketonuria (PKU) is a rare genetic disorder where the body cannot effectively process phenylalanine, an amino acid found in protein. Without the necessary enzyme, phenylalanine hydroxylase, phenylalanine accumulates to harmful levels in the blood and brain. Early and accurate diagnosis of PKU is crucial to prevent severe health problems.
Newborn Screening for PKU
Newborn screening is the primary method for identifying PKU shortly after birth. This routine screening is performed on nearly all babies, typically between 24 and 72 hours after birth. A simple heel prick test collects a few drops of blood onto a special filter paper, which is then sent to a laboratory for analysis.
The initial screening looks for elevated phenylalanine levels. Modern technology, such as tandem mass spectrometry (MS/MS), is commonly employed. This method measures phenylalanine and other amino acids, offering high sensitivity and specificity for detecting metabolic disorders, including PKU.
Confirmatory Testing
If newborn screening results indicate potential PKU, further tests confirm the diagnosis. This involves specific blood tests, such as quantitative plasma amino acid analysis, which precisely measures phenylalanine and other amino acid levels.
Genetic testing is also a crucial step in confirming a PKU diagnosis. This DNA analysis identifies mutations in the PAH gene, which provides instructions for the phenylalanine hydroxylase enzyme. Genetic testing helps determine the specific type and severity of PKU and differentiates it from other conditions that might cause elevated phenylalanine levels.
Diagnosis Beyond Newborn Screening
While most PKU cases are identified through newborn screening, some individuals are diagnosed later in childhood or adulthood. This occurs when symptoms prompt medical investigation.
These symptoms can include developmental delays, intellectual disabilities, seizures, hyperactivity, or behavioral problems. A distinctive musty odor in the breath, skin, or urine, and lighter skin and hair color may also be present. When such symptoms appear, blood tests and genetic analysis of the PAH gene are performed to establish a diagnosis.
Why Early Diagnosis Matters
Early diagnosis of PKU is important because it allows for prompt intervention, preventing severe health complications. Without timely diagnosis and treatment, phenylalanine accumulation can lead to significant brain damage, resulting in intellectual disability, neurological problems, and behavioral issues.
Starting treatment soon after birth, typically within the first few weeks, significantly reduces the risk of these severe outcomes. The primary treatment involves a low-phenylalanine diet, which restricts foods high in protein. This dietary management, often supplemented with specialized formulas, helps maintain phenylalanine levels within a safe range. Early and consistent dietary control enables individuals with PKU to achieve normal development and lead healthy lives.