Download the genetic polimorphism in pah gene at phenylketonuria moldavian

THE GENETIC POLIMORPHISM IN PAH GENE AT PHENYLKETONURIA MOLDAVIAN
PATIENTS (2010-2011)
BOICIUC Kiril, BURGOCI Vasile, SACARĂ Victoria
National Centre of Reproductive Health and Medical Genetics, Chisinau, Republic of Moldova
Reviewer: UŞURELU Natalia, MD, PhD
Keywords: PAH gene, phenylketonuria, mutation, phenylalanine, diagnostic
Introduction: Phenylketonuria (PKU) is an autosomal recessive pathology caused by deficiency of phenylalanine
hydroxylase enzyme (PAH), which catalyses the conversion of phenylalanine (Phe) into tyrosine. PAH gene is located
on chromosome 12q22-24 and contains 564 mutations. There was described 9 polymorphic sites of 7 restriction
endonucleases in PAH gene: Bgl II, Pvu II, EcoR I, Xmn I, Hind III, EcoR V, Msp I. Each combination of polymorphic
sites forms a haplotype used in indirect diagnosis due to its association with specific mutations in the PAH gene and is
transmitted together with the mutation.
Materials and methods: The study group was selected in 2010-2011 and it was consisting of patients with PKU
identified by neonatal screening (flourometric method), made obligatory for all newborns in Moldova. In the research
there were included the DNA of 4 PKU patients and their families who agreed the genetic analysis. For genetic analysis
of PAH gene the PCR-RFLP method for direct diagnosis determining mutations (R408W, P281L, R261Q, R252W,
R158Q, IVS10nt10) and indirect diagnosis by identifying the PAH gene polymorphisms (Bgl II, Pvu II, Xmn I, Msp I
VNTR) were used.
Results: During 2010-2011 in Moldova there were tested 78299 newborns by neonatal screening, the screening
rate being 97.1% and 99% respectively. The 800 newborns were suspected for PKU having the seric values of Phe more
than 3mg/dl. After retesting of suspected newborns there were identified 6 infants with PKU during this period. The
R408W mutation in homozygous state has been detected at 3 PKU patients (R408W/R408W) and in heterozygous
compound with P281L mutation at 1 PKU patient (R408W/P281L) through the direct diagnosis on PAH gene. The
indirect analysis of haplotypes of PAH gene showed the association of haplotype 2 containing 3 VNTR copies with
R408W mutation and of haplotype 1 containing 7 VNTR copies with P281L mutation. Identified mutations induce
classical form of PKU characterized by Phe blood level more than 15mg/dl. In 3 patients (75%) the initial Phe blood
level was determined more than 16mg/dl and blond phenotype was developed, but in one patient the amount of Phe
blood level was found 8.0 mg/dL at birth and dark phenotype indicating a moderate type of PKU instead of the classical
form predicted by genotype (R408W/R408W).
Conclusion: The analysis of the molecular structure of PAH gene determined that the R408W mutation is
associated with haplotype 2 containing 3 VNTR copies and the P281L mutation is associated with haplotype 1
containing 7 VNTR copies, being characteristic for Western-European population. Genotype-phenotype correlation in
PKU patients determined positive prediction of classic PKU in 75% of cases. Analyzing own material, we concluded
that the early diagnosis and start of dietary treatment are very important for good intellectual development in PKU
patients and clinical manifestations of PKU depend on more factors.
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