Spectrum and Frequency of Mutations in IMPDH1 Associated with Autosomal Dominant Retinitis Pigmentosa and Leber Congenital Amaurosis

Department of Biochemistry, Brandeis University, Волтам, Massachusetts, United States
Investigative Ophthalmology &amp Visual Science (Impact Factor: 3.4). 02/2006; 47(1):34-42. DOI: 10.1167/iovs.05-0868
Source: PubMed


The purpose of this study was to determine the frequency and spectrum of inosine monophosphate dehydrogenase type I (IMPDH1) mutations associated with autosomal dominant retinitis pigmentosa (RP), to determine whether mutations in IMPDH1 cause other forms of inherited retinal degeneration, and to analyze IMPDH1 mutations for alterations in enzyme activity and nucleic acid binding.
The coding sequence and flanking intron/exon junctions of IMPDH1 were analyzed in 203 patients with autosomal dominant RP (adRP), 55 patients with autosomal recessive RP (arRP), 7 patients with isolated RP, 17 patients with macular degeneration (MD), and 24 patients with Leber congenital amaurosis (LCA). DNA samples were tested for mutations by sequencing only or by a combination of single-stranded conformational analysis and by sequencing. Production of fluorescent reduced nicotinamide adenine dinucleotide (NADH) was used to measure enzymatic activity of mutant IMPDH1 proteins. The affinity and the specificity of mutant IMPDH1 proteins for single-stranded nucleic acids were determined by filter-binding assays.
Five different IMPDH1 variants, Thr116Met, Asp226Asn, Val268Ile, Gly324Asp, and His 372Pro, were identified in eight autosomal dominant RP families. Two additional IMPDH1 variants, Arg105Trp and Asn198Lys, were found in two patients with isolated LCA. None of the novel IMPDH1 mutants identified in this study altered the enzymatic activity of the corresponding proteins. In contrast, the affinity and/or the specificity of single-stranded nucleic acid binding were altered for each IMPDH1 mutant except the Gly324Asp variant.
Mutations in IMPDH1 account for approximately 2% of families with adRP, and de novo IMPDH1 mutations are also rare causes of isolated LCA. This analysis of the novel IMPDH1 mutants substantiates previous reports that IMPDH1 mutations do not alter enzyme activity and demonstrates that these mutants alter the recently identified single-stranded nucleic acid binding property of IMPDH. Studies are needed to further characterize the functional significance of IMPDH1 nucleic acid binding and its potential relationship to retinal degeneration.

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    • "To date, 18 different genes have been identified and mutations in any of these genes lead to the LCA phenotype: AIPL1 (Aryl-hydrocarbon-interacting protein-like1) (Sohocki et al., 2000), CEP290 (Centrosomal protein 290 kDa) (den Hollander et al., 2006), CRB1(Cone rod homeobox protein) (den Hollander et al., 2001), CRX (Crumbs Homolog 1) (Freund et al., 1998), GUCY2D (Retinal guanylate cyclase 2D) (Perrault et al., 1996), IMPDH1 (Inosine monophosphate dehydrogenase 1) (Bowne et al., 2006), IQCB1 (IQ motif containing B1) (Estrada-Cuzcano et al., 2011), KCNJ13 (Potassium inwardly-rectifying channel, subfamily J, member 13) (Sergouniotis et al., 2011), LCA5 (Leber congenital amaurosis 5) (den Hollander et al., 2007), LRAT (Lecithin retinol acyltransferase) (Thompson et al., 2001), MERTK (C-mer proto-oncogene tyrosine kinase) (Gal et al., 2000), NMNAT1 (Nicotinamide mononucleotide adenylyltransferase 1) (Chiang et al., 2012; Falk et al., 2012; Koenekoop et al., 2012; Perrault et al., 2012), RD3 (Retinal degeneration 3) (Friedman et al., 2006), RDH12 (Retinol dehydrogenase 12) (Perrault et al., 2004), RPE65 (Retinal pigment epithelium specific protein 65 kDa) (Marlhens et al., 1997), RPGRIP1 (Retinitis pigmentosa GTPase regulator interacting protein 1) (Dryja et al., 2001), SPATA7 (Spermatogenesis associated 7) (Wang et al., 2009), and TULP1 (Tubby-like protein 1) (Hanein et al., 2004). While the most frequently mutated genes are CEP290 "
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    ABSTRACT: Leber congenital amaurosis (LCA) causes severe visual impairment and blindness very early in life. Mutant alleles of several genes acting in different pathways, of which all have critical roles for normal retinal function, were involved in LCA development. The purpose of this study was to use genome-wide genotyping to identify LCA-causing loci in two Turkish families. Genome-wide genotyping and haplotype analysis were performed for prioritization of candidate genes for mutation screening in families with LCA. Identified informative critical choromosomal regions obtained by homozygosity mapping from the families were searched for overlapping of any LCA causative genes. Corresponding clinical phenotypes of the patients with identified mutations were evaluated. In this study, two families were shown to be linked to two different LCA loci covering retinol dehydrogenase 12 (RDH12) and aryl-hydrocarbon-interacting protein-like1 (AIPL1) genes. Mutation screening revealed a novel p.Gln141* mutation in the AIPL1 gene and a previously described p.Thr49Met mutation in the RDH12 gene in a homozygous state. Our patients with the RDH12 mutation had the distinct macular coloboma sign, and the patient with the AIPL1 mutation developed microphthalmia and severe widespread retinal pigment epithelial atrophy, in contrast to previously reported cases. It is currently evident that mutation screening needs to be done in at least 18 genes known to be associated with LCA. Thus, homozygosity mapping is an alternative technique to improve the molecular diagnosis in LCA, which is a group of genetically and clinically heterogeneous diseases causing retinal degeneration. The patients without mutation in known genes may further be analyzed by using next-generation sequencing.
    DNA and Cell Biology 08/2014; 33(12). DOI:10.1089/dna.2014.2554 · 2.06 Impact Factor
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    • "The occurrence of disease-causing mutations in and around the Bateman domain of IMPDH1, which have no effect on enzymatic activity [10], [11], [12], together with our findings from the chimeras suggests a physiologically important role of a regulatory region outside the catalytic site of the enzyme. Currently, there is no consensus as to the molecular effects yielded by RP-causing mutations in IMPDH1 and intriguingly, the reported properties are divergent between the R224P and D226N mutants [10], [11], [12], [44], [45], [46]. "
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    ABSTRACT: We recently reported that Inosine Monophosphate Dehydrogenase (IMPDH), a rate-limiting enzyme in de novo guanine nucleotide biosynthesis, clustered into macrostructures in response to decreased nucleotide levels and that there were differences between the IMPDH isoforms, IMPDH1 and IMPDH2. We hypothesised that the Bateman domains, which are present in both isoforms and serve as energy-sensing/allosteric modules in unrelated proteins, would contribute to isoform-specific differences and that mutations situated in and around this domain in IMPDH1 which give rise to retinitis pigmentosa (RP) would compromise regulation. We employed immuno-electron microscopy to investigate the ultrastructure of IMPDH macrostructures and live-cell imaging to follow clustering of an IMPDH2-GFP chimera in real-time. Using a series of IMPDH1/IMPDH2 chimera we demonstrated that the propensity to cluster was conferred by the N-terminal 244 amino acids, which includes the Bateman domain. A protease protection assay suggested isoform-specific purine nucleotide binding characteristics, with ATP protecting IMPDH1 and AMP protecting IMPDH2, via a mechanism involving conformational changes upon nucleotide binding to the Bateman domain without affecting IMPDH catalytic activity. ATP binding to IMPDH1 was confirmed in a nucleotide binding assay. The RP-causing mutation, R224P, abolished ATP binding and nucleotide protection and this correlated with an altered propensity to cluster. Collectively these data demonstrate that (i) the isoforms are differentially regulated by AMP and ATP by a mechanism involving the Bateman domain, (ii) communication occurs between the Bateman and catalytic domains and (iii) the RP-causing mutations compromise such regulation. These findings support the idea that the IMPDH isoforms are subject to distinct regulation and that regulatory defects contribute to human disease.
    PLoS ONE 12/2012; 7(12):e51096. DOI:10.1371/journal.pone.0051096 · 3.23 Impact Factor
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    • "The prevalence of LCA is around one to two per 80,000 live births, accounting for approximately 20% of cases of inherited blindness among children in institutes for the blind and more than 5% of all congenital retinopathies. At present, 18 LCA loci have been mapped, in which 17 causative genes have been identified: guanylate cyclase 2D (GUCY2D) [4], crumbs homolog 1 (CRB1) [5], retinal pigment epithelium-specific protein 65 kDa (RPE65) [6], retinitis pigmentosa GTPase regulator interacting protein 1 (RPGRIP1) [7], aryl hydrocarbon receptor interacting protein-like 1 (AIPL1) [8], Leber congenital amaurosis 5 (LCA5) [9], cone-rod homeobox (CRX) [10], lecithin retinol acyltransferase (LRAT) [11], tubby like Protein 1(TULP1) [12], retinol dehydrogenase 12 (RDH12) [13], centrosomal Protein 290 kDa (CEP290) [14], retinal degeneration 3 (RD3) [15], spermatogenesis associated 7 (SPATA7) [16], (inosine 5′-monophosphate [IMP]) dehydrogenase 1 (IMPDH1) [17], orthodenticle homeobox 2 (OTX2) [18], IQ motif containing B1 (IQCB1) [19], and calcium binding protein 4 (CABP4) [20]. Although LCA was mostly thought to be transmitted as a recessive and dominant trait [2], some LCA cases show a triallelic or digenic inheritance [21,22]. "
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    ABSTRACT: To identify the causative gene for autosomal recessive Leber congenital amaurosis (LCA) in a Chinese family. One Chinese LCA family was identified and an ophthalmologic examination was performed. The genetic defects were analyzed simultaneously by a genome-wide linkage scan with 382 polymorphic microsatellite markers, as well as by comprehensive mutational screening of 15 genes known to associate with LCA on the genomic DNA of this family. Suggestive linkages were found in 13 chromosomal regions, of which only one harbored a known causative gene, crumbs homolog 1 (CRB1), on chromosome 1. Sanger sequencing of CRB1 identified two novel heterozygous mutations, c.3221T>C (p.L1074S) and c.2677-2A>C. In addition, a novel missense heterozygous mutation, c.938C>A (p.A313D), in spermatogenesis associated 7 (SPATA7), was detected in the proband after screening of the other 14 LCA causative genes. All three affected individuals of the family had compound heterozygous CRB1 mutations, and one of the three (the proband) had an additional mutation in SPATA7. The unaffected mother had the heterozygous c.3221T>C mutation in CRB1 and the heterozygous c.938C>A mutation in SPATA7. The unaffected father could not be tested, but presumably had the heterozygous c.2677-2A>C mutation in CRB1. The proband, with triallelic mutations in CRB1 and SPATA7, had a phenotype similar to other two affected brothers, suggesting the additional mutant allele in SPATA7 might not contribute to the disease. Similarly, the mother, with digenic mutations in CRB1 and SPATA7, had normal vision and fundi, suggesting the digenic mutations in these two genes might not cause disease. Digenic and triallelic mutations of CRB1 and SPATA7 were detected in a family with LCA. Our results imply that CRB1 and SPATA7 may not interact with each other directly. This emphasizes that care should be taken in invoking a mutation-disease association for digenic and triallelic mutations.
    Molecular vision 12/2011; 17:3326-32. · 1.99 Impact Factor
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