| Summary: | 碩士 === 國立陽明大學 === 遺傳學研究所 === 94 === Propionyl-CoA carboxylase (PCC, EC 6.4.1.3) is a mitochondrial, biotin-dependent enzyme that functions in the catabolism of branched-chain amino acids, fatty acids with odd-numbered chain lengths, and other metabolites. It catalyzes the ATP dependent carboxylation of propionyl-CoA to D-methylmalonyl CoA. Deficiency of PCC results in propionic acidemia (PA, MIM 232000, 232050) , a rare autosomal recessive metabolic disorder characterized by severe metabolic ketoacidosis, vomiting, lethargy, and hypotonia. PA can be life threatening. Human PCC is a dodecamer composed of pairs of nonidentical alpha and beta subunits encoded by PCCA and PCCB genes, which have been mapped to chromosomes 13 and 3, respectively.
In this study, we tried to identify the mutations causing PA in seven Chinese PA families. All patients were screened by sequencing products obtained after amplification of the 24 PCCA exons and 15 PCCB exons from genomic DNA. Using this approach, a total of 8 of the 14 mutant chromosomes has been defiend. Seven different mutations detected, namely c.229C>T (R77W), c.245G>A (C82Y), c.863G>A (R288K), c.1079T>G (V360G), c.1262A>C (Q421P) in the PCCA gene and c.1253C>T (A418V), c.1301C>T (A434V) in the PCCB gene. Two transistions, PCCA c.229C>T and PCCB c.1301C>T, had been reported in other PA patients. The PCCA c.229C>T mutation had been proved to be disease causing mutaion by functional analysis previously. The PCCA c.245G>A, c.863G>A, c.1079T>G, c.1262A>C and PCCB c.1253C>T are novel mutations identified by this study. By Southern blot analysis, we also found a large scale 8052 bp deletion cross exon 1 (Ch3: 137,447,747 bp ~ 137,455,811 bp; NCBI Build 35, May 2004 Assembly, hg17; http://genome.ucsc.edu/; GeneBank Access. No.: AY035786-AY035808) in the PCCB gene from two unrelated Chinese PA patients. This deletion is likely a disease causing mutation.
The PCCA c.229C>T mutation were found in two unrelated Chinese PA patients. Using microsatellite analysis by STR markers near or on the PCCA gene (D13S779, D13S1232, D13S1240, D13S1240) , we found these two c.229C>T mutant alleles linking to diffenent microsatellite marker allele. The c.229C>T has also been identified in other populations. Besides c.229C>T is located at a CpG site, which sustains a higher mutation rate. It suggested that the PCCA c.229C>T found in Chinese patinets may be independent sporadic mutations and may not be caused by a founder mutation.
Linkage analysis of the PCCB 8052 bp deletion with two closely linked markers, D3S3528 and D3S2453, found that the deletion mutant alleles of two unrelated Chinese PA patients have the same haplotype (D3S3528, D3S2453 : 266, 324 bp). The result suggested that this mutation may be caused by a founder mutation. Linkage analysis of the PCCB mutation c.1301C>T with a closely linked marker, D3S3528, revealed a high degree of linkage disequlibrium between one specific allele (270 bp) and the c.1301C>T found in 4 unrelated Chinese PA patients. It indicated that this mutation may be also caused by a founder mutation in the Chinese PA patients.
Our study of mutations and linkage analysis of the PCCA and PCCB gene in Chinese PA patients can be used in aid of carrier detection and prenatal diagnosis. Further studies in functional expression are necessary to confirm those mutaions are disease causing mutations and to delineate the structural and functional effects of these mutaions.
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