Classic phenylketonuria: diagnosis through heterozygote detection

Area of Science:

• Biochemistry
• Genetics
• Clinical Diagnostics

Background:

• Phenylketonuria (PKU) is an inherited metabolic disorder.
• Accurate genotyping is crucial for managing PKU and its variants.
• Distinguishing between PKU, carriers, and hyperphenylalaninemia requires reliable diagnostic methods.

Purpose of the Study:

• To develop and validate a novel genotyping method for differentiating classic PKU from heterozygosity.
• To apply this method in diverse clinical scenarios for accurate diagnosis.

Main Methods:

• Quantification of blood phenylalanine (P) and tyrosine (T) using ion-exchange chromatography.
• Calculation of an empiric determinant (P-2/T) and a discriminant function (sigma = a(1)(P)+a(2)(T)).
• Multivariate analysis was used to compute coefficients a(1) and a(2) for the discriminant function.

Main Results:

• The developed genotyping method successfully differentiated obligate heterozygotes from normal controls.
• The method was applied in three families, correctly identifying classic PKU and differentiating it from hyperphenylalaninemia.
• Maternal PKU's association with microcephaly in affected siblings was noted.

Conclusions:

• The described genotyping method provides a reliable approach for PKU diagnosis.
• This technique aids in distinguishing between classic PKU, hyperphenylalaninemia, and carrier states.
• Accurate genetic diagnosis is essential for clinical management and genetic counseling in PKU families.