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Phenylketonuria missense mutations in the Mediterranean
Y Okano1, T Wang, R C Eisensmith
1Howard Hughes Medical Institute, Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Genomics
|January 1, 1991
Summary
Two novel phenylalanine hydroxylase (PAH) gene mutations, R252W and P281L, cause severe phenylketonuria (PKU) in an Italian patient. These mutations, prevalent in the Italian population, suggest a Mediterranean origin.
Area of Science:
- Genetics
- Biochemistry
- Molecular Biology
Background:
- Phenylketonuria (PKU) is a genetic disorder caused by mutations in the phenylalanine hydroxylase (PAH) gene.
- The PAH gene encodes an enzyme crucial for metabolizing phenylalanine, an amino acid.
- Mutations in PAH lead to phenylalanine accumulation, causing severe neurological damage if untreated.
Purpose of the Study:
- To identify and characterize novel mutations in the PAH gene associated with PKU in an Italian patient.
- To investigate the functional consequences of identified mutations on PAH enzyme activity and protein levels.
- To determine the population frequency and origin of these mutations within the Italian population.
Main Methods:
- DNA sequencing to identify mutations in the PAH gene.
- Construction and transfection of expression vectors with normal and mutant PAH cDNA into mammalian cells.
- Enzyme activity assays and Western blot analysis to assess PAH protein function and expression.
- Population genetic studies, including RFLP analysis and haplotype association.
Main Results:
- Two missense mutations, R252W and P281L, were identified in exon 7 of the PAH gene.
- Both mutations resulted in negligible PAH enzyme activity and undetectable protein levels in transfected cells.
- R252W and P281L mutations are in linkage disequilibrium with the prevalent Italian RFLP haplotype 1.
- R252W and P281L mutations account for 10% and 20% of haplotype 1 mutant chromosomes, respectively.
- These mutations are rare in other European populations, suggesting a Mediterranean origin.
Conclusions:
- The identified R252W and P281L mutations are causative of severe classical PKU.
- The functional deficiency observed in vitro correlates with the patient's severe PKU phenotype.
- The high prevalence and linkage to haplotype 1 in the Italian population indicate a specific founder effect or selective pressure within this demographic, likely of Mediterranean origin.