Background: Alkaptonuria (AKU) is a rare tyrosine metabolism disorder caused by homogentisate 1,2-dioxygenase (HGD) mutations and homogentisic acid (HGA) accumulation. In this study, we investigated the genotype-phenotype relationship in AKU patients with a novel HGD gene mutation from a Chinese Hani family.
Methods: Routine clinical examination and laboratory evaluation were performed, urine alkalinization test and urinary gas chromatography-mass spectrometry were used to assess HGA. Gene sequencing was utilized to study the defining features of AKU. NetGene2-2.42 and BDGP software was used to predict protein structure online. Flow cytometry and RT-PCR were used to analyze HGD proteins and HGD mRNA, respectively.
Results: Two pediatric patients fulfilled diagnostic criteria for AKU with eddish-brown or black diapers and urine HGA testing. Sequencing testing revealed that all members of this family had a novel samesense mutation c.15G > A at the edge of exon 1 of the HGD. By flow cytometry, the expression of HGD protein in the pediatric patients' peripheral blood mononuclear cells was barely expressed. NetGene2-2.42 and BDGP software showed that the mutation reduced the score of the 5' splice donor site and disrupted its normal splicing, and the RT-PCR product also demonstrated that the defect in the HGD protein was due to the lack of the first exon containing the start codon ATG after the mutation.
Conclusions: The novel mutation c.15G > A in HGD is associated with the AKU phenotype. It may affect the splicing of exon 1, leading to exon skipping, which impairs the structure and function of the protein.
Keywords: AKU; Alkaptonuria; HGD; Homogentisate 1,2-dioxygenase; Homogentisic acid; Mutation.
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