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Ординатура / Офтальмология / Английские материалы / Retinal Degenerative Diseases Laboratory and Therapeutic Investigations_Anderson_2008.pdf
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L. Shumei et al.

2008). It is one of the leading causes of blindness in adults with an incidence of around 1 in 3,500 worldwide (Hims et al. 2003). RP has a strong genetic component with multiple modes of inheritance including autosomal dominant (adRP), autosomal recessive (arRP), X-linked (xLRP) and apparent digenic forms (Wang et al. 2001). The autosomal dominant forms have been associated with 16 different loci, and for 15 of these, the causative genes have been identified including: PRPF3 (1q21.2), SEMA4A (1q22), RHO (3q22), GUCA1B (6p21.1), RDS(6p21.2), RP9 (7q14), IMPDH1 (7q32), RP1 (8q12), ROM1 (11q12), NRL (14q11), PRPF8 (17p13), CA4 (17q23), FSCN2 (17q25), CRX (19q13.3), and PRPF31 (19q13.4) (Zhao et al. 2006).

Inosine monophosphate dehydrogenase (IMPDH) proteins form homotetramers and catalyze the rate limiting step of de novo guanine synthesis by oxidizing IMP to xanthosine-5 -monophosphate (XMP) with reduction of nicotinamide adenine dinucleotide (NAD). Two closely related human IMPDH isoforms, types 1 and 2, have been identified, each consisting of 514 amino acids with 84% sequence identity. IMPDH genes are found in virtually every organism, and the gene and amino acid sequences are highly conserved across species. The isoforms are encoded by 2 distinct genes, IMPDH1 and IMPDH2 (inosine monophosphate dehydrogenase 1 and 2), located at 7q31.3–q32 and 3p21.2–p24.2, respectively. Gene expression of the 2 isoforms is differently regulated in various tissues and cell populations, and they are not mutually redundant (Bremer et al. 2007). Mutations in IMPDH1 cause the RP10 form of autosomal dominant RP (adRP) (Kennan et al. 2002). IMPDH1 is located on chromosome 7q32.1 and encodes the enzyme IMPDH1.

In this study, we surveyed a population of patients with adRP to determine the range and the frequency of IMPDH1 mutations. The clinical heterogeneity of mutations in genes associated with retinal degeneration has been demonstrated many times (Bowne et al. 2006). Therefore, we analyzed patients with specifically autosomal recessive RP (arRP) to investigate the possibility that mutations in IMPDH1 cause alternate phenotypes.

33.2 Materials and Methods

33.2.1 Subjects

This study was performed in accordance with the Declaration of Helsinki, with informed consent obtained in all cases. Most subjects examined in this study were diagnosed at one of the following sites: (1) Department of Ophthalmology of the 1st Affiliated Hospital, Gannan Medical College; (2) Department of Ophthalmology of the People Hospital of Ganzhou City. The research at each academic institution was approved by the respective human subjects’ review board.

33 Mutation Frequency of IMPDH1 Gene of Han Population in Ganzhou City

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33.2.2 DNA Extraction

The whole blood samples were collected randomly from 56 adRP patients and 62 unrelated normal controls who were residents of Han population in Ganzhou City, and then their genomic DNA samples were extracted respectively by the DNA extraction kit (Shenggong, PRC).

33.2.3 Amplification of IMPDH1 Genes

Exon 7 of the IMPDH 1 gene was amplified by PCR. According to the reference (Yu et al. 2007), the peculiar primes were 5 -CAGTGGAATCTCTGGAGTGGTC- 3 and 5 -CCT2GGGTCCTCATAAACCTC-3 which were synthesized by Shanghai Shenggong biology engineering company. The total volume of polymerase chain reaction (PCR) was 10 ul which included 6 ul of DNA sample, 2 pmol of positive prime and negative prime respectively, 2.5 mmol/L dNTP, 1 ul of 10 × PCR Buffer and 0.5 U Taq DNA polymerase enzyme. All PCRs were carried out in a SX-240B thermal cycler (Shunda, PRC). The reactions were incubated for 10 min at 96C which was followed by 34 cycles of denaturation (96C, 1 min), annealing (50C,

30 s), extension (68C, 3 min), final extension (68C, 10 min) and were then held at 4C.

33.2.4 RFLP Analysis

Msp restriction endonuclease (Shenggong, PRC) was selected for DNA digestion. The volume of enzymatical digestion was 20 ul. IMPDH 1 gene amplicons (10 ul/reaction) of each sample were enzymatically digested by Msp I(0.2 ul/ reaction) at 37C for 9 h. PCR-product restriction fragments (20 ul) were separated by electrophoresis (TAE buffered agarose gels) at 5 V/cm for 2 h and stained with ethidium bromide. Each gel included 50 bp DNA ladder markers. RFLPs were visualized using UV light, and images were recorded using a Gel Documentation Digital Imaging system.

33.2.5 Statistical Analysis

The statistical significance of the data was further analyzed by SPSS 14.0 software. The rates were compared by χ2 test, and α = 0.05 was size of test.