| [Abstract] Objective To investigate the clinical features and FAH gene mutations of three Chinese children with tyrosinemia type I. Method In accordance with the diagnostic criteria provided by the International Organization for Rare Disorders, Clinical records of three cases were reviewed. Genomic DNA was extracted from peripheral blood leukocytes with QIAamp DNA Mini Kit.The patients were subjected to direct sequencing14exons together with100bp adjacent fragments of FAH gene using ABI Prism3730Genetic Analyzer (Applied Biosystems Foster City, CA) after PCR based on genomic DNA. The sequencing map were manually analyzed by BioEdit software and aligned with genome sequence by Pubmed Blast tool for excluding known SNP loci before searching1000genomes database or dbSNP137. The mutation source was verified by analyzing parents’exons corresponding to patients’mutation exons. The homology between human FAH enzyme and that of other species was survyed using software Clustal X (European Bioinformatics Institute, Hinxton, Saffron Walde, UK). Polyphen (Polymorophism Phenotyping), available online, were used to predict possible impact of an amino acid substitution on structure and function of FAH enzyme. Polyphen calculates position-specific independent counts(PSIC) scores for two amino acid variants in polymorphic position. A PSIC scores that differ by>2were regarded as indicating the probability of damaging variants, PSIC≤0.5non-pathogenic mutation;0.5<PSIC≤1.5, mutation significance is judged from nature of amino acids;1.5<PSIC≤2, possibility of disease-causing mutations; Result Patien1was a5months and21days old boy who suffered from persistent diarrhea, hepatomegaly, ascites;Alpha fetoprotein>1210μg/L, levels of tyrosine in blood and succinylacetone in urine were110.8μmol/L and83.7μmol/L.His sister suffered from Tyrosinemia type I.Direct sequencing showed a G to A transition in CDS position455and 1027. He is compound heterozygous for the mutation c.455G> A/c.1027G> A, which predicts a change from trptophan to a stop codon at positon152(W152X), and a change from glycine to arginine at position343respectively(W343R). Patient2was a6-year and1-month old girl with late-onset rickets who had signs of hepatosplenomegaly,rachitic bones,windswept knees.Hypophosphatemia0.54mmol/L and alkaline phosphatase1620IU/L were detected. Normal serum calcium. Alpha fetoprotein412.8μg/L, levels of tyrosine in blood and succinylacetone in urine were835.8μmol/L and27.48μmol/L. Rikets did not improve after administration of calcium and vitamine D3. Her grandparents are intermarrige. She is homozygous for the mutation c.1027G>A, which predicts G343R.The parents were mutation carriers. Analysis by Clustal X on the alignment of amino acids residual reservation among different species showed that the locative amino acid was highly conserved. Polyphen software predict G343R was probably damaging (PSIC score3.235). Patient3, a2-year4-month old boy, whose chief complaint is intermittent fever with vomiting and diarrhea, had hepatomegaly, Hypophosphatemia0.51mmol/L,alkaline phosphatase628IU/L, alpha-fetoprotein1136μg/L, blood tyrosine543.26mol/L, urine succinylacetone32.35μmol/L. Exonl fails to be amplificated repeadedly. Conclusion For children with tyrosinemia type Ⅰ can have manifestations of persistent diarrhea or late-onset richets. Physical examination can reveal hepatomegaly, laboratory tests indicate hypophosphatemia and markedly elevated concentrations of alpha-fetoprotein and alkaline phosphatase in plasma and succinylacetone in urea, other members in family may have tyrosinemias or be consanguineous, Muation c.455G> A and c.1027G>A can be detected in Chinese patients with Tyrosinemia type Ⅰ. |
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