Adenine Phosphoribosyltransferase Gene Research Articles

Determination of spontaneous loss of heterozygosity mutations in Aprt heterozygous mice.

A mouse model was generated to investigate loss of heterozygosity (LOH) events in somatic cells. The adenine phosphoribosyltransferase ( Aprt ) gene was disrupted in embryonic stem cells using a conventional gene targeting approach and subsequently Aprt hetero-zygous and homozygous mice were derived. Aprt homozygous deficient animals were viable though the mendelian inheritance pattern was skewed. On average these mice died at 6 months of age from severe renal failure. In T-lymphocytes of Aprt heterozygous mice the mean spontaneous mutant frequency at the Aprt locus was 8.7 x 10(-6) while the frequency was 0.8 x 10(-6) at the hypoxanthine phosphoribosyltransferase locus. In order to determine whether LOH events contribute to the high spontaneous mutant frequency at the Aprt locus, 140 Aprt mutant T-lymphocyte clones were expanded and analysed by allele-specific PCR. In 97 (69%) of these clones the wild-type allele had been lost. Nine of the mutant clones were characterized in more detail using dual-coloured fluorescence in situ hybridization analysis. Five out of six of the mutant clones which arose from an LOH event, based on the PCR assay, contained a duplication of the targeted allele. Therefore, mitotic recombination or chromosome loss followed by duplication of the remaining homologue appears to be the predominant mechanism for the in vivo generation of Aprt mutant T-lymphocytes.

Gene silencing by DNA methylation and dual inheritance in Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells strain D422, which has one copy of the adenine phosphoribosyl transferase (APRT) gene, were permeabilized by electroporation and treated with 5-methyl deoxycytidine triphosphate. Cells with a silenced APRT gene were selected on 2, 6-diaminopurine. Colonies were isolated and shown to be reactivated to APRT+ by 5-aza-cytidine and by selection in medium containing adenine, aminopterin and thymidine. Genomic DNA was prepared from eight isolates of independent origin and subjected to bisulphite treatment. This deaminates cytosine to uracil in single-stranded DNA but does not deaminate 5-methyl cytosine. PCR, cloning and sequencing revealed the methylation pattern of CpG doublets in the promoter region of the APRT- gene, whereas the active APRT gene had nonmethylated DNA. CHO strain K1, which has two copies of the APRT+ gene, could also be silenced by the same procedure but at a lower frequency. The availability of the 5-methyl dCTP-induced silencing, 5-aza-CR and a standard mutagen, ethyl methane sulphonate, makes it possible to follow concomitantly the inheritance of active, mutant or silenced gene copies. This analysis demonstrates "dual inheritance" at the APRT locus in CHO cells.

The origin of APRT*J. The most common disease-related mutation of APRT gene among Japanese goes back to a prehistoric era.

Adenine phosphoribosyltransferase (APRT) converts adenine into AMP in the presence of 5-phosphoribosyl-l-pyrophosphate. When this enzyme is genetically deficient, 2,8-dihydroxyadenine (DHA) urolithiasis may occur.1 It is usually considered that an individual develops DHA urolithiasis only when the subject is homozygous (both of the APRT alleles are defective) although one report described the development of the lithiasis in a heterozygote.2 KeywordsMutant AlleleKorean PeninsulaHomozygous IndividualDefective AlleleAdenine PhosphoribosyltransferaseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Relationship of the two APRT gene products from Saccharomyces cerevisiae.

Adenine phosphoribosyltransferase (APRT) is a key component of the nucleotide salvage pathway converting free adenine plus 5′-phospho-ribosylpyrophosphate (PRPP) to 5′-adenosine monophosphate (AMP) plus pyrophosphate. This enzyme is ubiquitous in all organisms examined. In some parasitic organisms, which lack a de novo purine synthesis, APRT is the only means by which AMP is formed.1 APRT deficiency in humans and mice leads to the accumulation of highly insoluble 2,8-dihydroxy adenine.2,3 This can lead to kidney stones and possible kidney failure.2,3

Recombination-dependent deletion formation in mammalian cells deficient in the nucleotide excision repair gene ERCC1.

Nucleotide excision repair proteins have been implicated in genetic recombination by experiments in Saccharomyces cerevisiae and Drosophila melanogaster, but their role, if any, in mammalian cells is undefined. To investigate the role of the nucleotide excision repair gene ERCC1, the hamster homologue to the S. cerevisiae RADIO gene, we disabled the gene by targeted knockout. Partial tandem duplications of the adenine phosphoribosyltransferase (APRT) gene then were constructed at the endogenous APRT locus in ERCC1- and ERCC1+ cells. To detect the full spectrum of gene-altering events, we used a loss-of-function assay in which the parental APRT+ tandem duplication could give rise to APRT- cells by homologous recombination, gene rearrangement, or point mutation. Measurement of rates and analysis of individual APRT- products indicated that gene rearrangements (principally deletions) were increased at least 50-fold, whereas homologous recombination was affected little. The formation of deletions is not caused by a general effect of the ERCC1 deficiency on gene stability, because ERCC1- cell lines with a single wild-type copy of the APRT gene yielded no increase in deletions. Thus, deletion formation is dependent on the tandem duplication, and presumably the process of homologous recombination. Recombination-dependent deletion formation in ERCC1- cells is supported by a significant decrease in a particular class of crossover products that are thought to arise by repair of a heteroduplex intermediate in recombination. We suggest that the ERCC1 gene product in mammalian cells is involved in the processing of heteroduplex intermediates in recombination and that the misprocessed intermediates in ERCC1- cells are repaired by illegitimate recombination.

Cloning and characterization of a relA/spoT homologue from Bacillus subtilis.

A PCR-amplified DNA fragment of the relA gene from genomic Bacillus subtilis DNA was used to isolate the entire relA/spoT homologue and two adjacent open reading frames (ORFs) from a lambda ZAP Express library. The relA gene, which encodes a protein of 734 amino acid residues (aa), is flanked by an ORF (170aa) that shares high similarity to adenine phosphoribosyltransferase genes (apt), and downstream by an ORF (131 aa) of unknown function. This genetic organization is similar to that in Streptomyces coelicolor A3(2) and Streptococcus equismilis H46A. relA shows significant similarity to the Escherichia coli relA and spoT genes, which are responsible for the synthesis and degradation of the highly phosphorylated guanosine nucleotides (p)ppGpp, triggering the stringent response. Deletion of the relA gene generated a (p)ppGpp0 phenotype that demonstrated its essential role in the response to amino acid deprivation and resulted in impaired/lowered induction of proteins involved in stress response as well as amino acid biosynthesis, as judged by two-dimensional gel electrophoresis. The same effects of impaired induction of some sigmaB-independent proteins could also be shown in a sigB/relA double mutant, supporting the role of relA in derepression/induction of catabolic and anabolic genes during stringent response.

A germline partial deletion of adenine phosphoribosyltransferase gene presumably related to the suppression of loss of heterozygosity in somatic cells

A germline partial deletion of adenine phosphoribosyltransferase gene presumably related to the suppression of loss of heterozygosity in somatic cells

Plasmodium falciparum hypoxanthine-guanine phosphoribosyltransferase as a chemotherapeutic target: Comparison of the human and parasite enzymes

A conditionally lethal mutant of Leishmania donovani that lacks both hypoxanthine-guanine phosphoribosyltransferase and xanthine phosphoribosyltransferase exhibits a strikingly restricted growth phenotype, can only survive as the promastigote under pharmacological constraints, and is profoundly compromised in its ability to infect macrophages and mice. Interestingly, the conditionally lethal growth phenotype displayed by these mutant parasites can be suppressed in vitro by selection of strains that have markedly amplified the adenine phosphoribosyltransferase gene on extrachromosomal elements that are unique to these suppressor strains. Employing pulsed field gel electrophoresis, we have now determined that the amplicons in two of these suppressor lines are linear molecules by: (1) their pulse time-dependent mobility; (2) the failure of γ-irradiation to generate new discrete bands; (3) their susceptibility to λ exonuclease digestion; and (4) the presence of telomeric sequences. Pulsed field gel electrophoresis also shows these amplicons to be approximately 200–275 kb in size. However, quantitative polymerase chain reaction and Southern blot analyses demonstrated that the amplification units are ∼40 kb in length, implying that the formation of these amplicons involved additional chromosomal rearrangements or oligomerization.

Molecular evidence for the induction of large interstitial deletions on mouse chromosome 8 by ionizing radiation

The P19H22 mouse embryonal carcinoma cell line is characterized by a hemizygous deficiency for the chromosome 8 encoded aprt (adenine phosphoribosyltransferase) gene and heterozygosity for many chromosome 8 loci. We have previously demonstrated that this cell line is suitable for mutational studies because it is permissive of events ranging in size from base-pair substitutions at the aprt locus to apparent loss of chromosome 8. Large mutational events, defined by loss of the remaining aprt allele, were found to predominate in spontaneous mutants and those induced by ionizing radiation (Turker et al., Mutation Res., 329, 97–105, 1995). In this study we have used a PCR based assay to screen for loss of heterozygosity at microsatellite loci both proximal and distal to aprt in 137Cs-induced and spontaneous aprt mutants. This approach allowed us to distinguish apparent interstitial deletional events from apparent recombinational events. Significantly, 32.5% (26 of 80) of the mutational events induced by 137Cs appeared to be interstitial deletions as compared with 7.7% (6 of 78) in the spontaneous group. This difference was statistically significant ( p<0.0001) suggesting that exposure to 137Cs caused a significant number of deletion mutations. Most 137Cs-induced interstitial deletions were larger than 6 cM, whereas none of the spontaneous deletions were larger than 6 cM. These results provide further support for the notion that ionizing radiation induces deletion mutations and validate the use of the P19H22 cell line for the study of events induced by ionizing radiation.

Repair of site-specific double-strand breaks in a mammalian chromosome by homologous and illegitimate recombination.

In mammalian cells, chromosomal double-strand breaks are efficiently repaired, yet little is known about the relative contributions of homologous recombination and illegitimate recombination in the repair process. In this study, we used a loss-of-function assay to assess the repair of double-strand breaks by homologous and illegitimate recombination. We have used a hamster cell line engineered by gene targeting to contain a tandem duplication of the native adenine phosphoribosyltransferase (APRT) gene with an I-SceI recognition site in the otherwise wild-type APRT+ copy of the gene. Site-specific double-strand breaks were induced by intracellular expression of I-SceI, a rare-cutting endonuclease from the yeast Saccharomyces cerevisiae. I-SceI cleavage stimulated homologous recombination about 100-fold; however, illegitimate recombination was stimulated more than 1,000-fold. These results suggest that illegitimate recombination is an important competing pathway with homologous recombination for chromosomal double-strand break repair in mammalian cells.

Loss of heterozygosity analysis in a human fibrosarcoma cell line.

Loss of heterozygosity (LOH) is an important event in tumor formation. We have used polymorphic microsatellite repeat markers to identify and characterize LOH in spontaneous mutants of a human cell line, MR12-1, that is heterozygous for the adenine phosphoribosyltransferase gene (APRT+/-) located on chromosome 16q24.3. Initially, clones without extensive LOH (which are likely derived as a consequence of intragenic point mutations) and clones with multilocus LOH (which are likely due to major chromosome alterations) were identified. Clones with major regions of LOH were further characterized by assaying additional informative microsatellite markers. Analysis of 20 spontaneously-arising, independent APRT-/- clones from MR12-1 demonstrated that nine of the mutants retained both copies of APRT and 11 had undergone multilocus genetic alterations. The nature of LOH in four of the latter clones has been examined in detail by karyotype and fluorescence in situ hybridization analysis (Shao et al., 1996). These data demonstrate that LOH of chromosome 16 may be due to mitotic recombination, interstitial or partial deletion, or to more complex mechanisms. LOH in these clones may be a consequence of events similar to those observed in many tumors.

A role for certain mouse Aprt sequences in resistance to toxic adenine analogs.

A mouse embryonal carcinoma cell line hemizygous for the adenine phosphoribosyltransferase gene (aprt) was exposed to ultraviolet light (UV) or to the alkylating agent, ethyl methanesulfonate (EMS). Thirty eight cell lines retaining the aprt gene were isolated by selecting for resistance to 2,6-diaminopurine (DAP), an adenine analogue which selects against aprt activity. Of these, six cell lines distinguished by significant levels of aprt enzymatic activity after selection in DAP, were found to carry mutations in the aprt gene affecting the apparent Km of the enzyme for adenine in every cell line, and the apparent Km for phosphoribosylpyrophosphate in two of the six cell lines. The results indicate that the ability of these cells to survive in the presence of toxic adenine analogues while maintaining significant levels of aprt enzyme activity may be due to a reduced affinity for the adenine analogue, DAP. This biochemical analysis along with results obtained from sequencing the aprt gene from 31 DAP resistant cell lines with no detectable aprt activity were used to implicate certain amino acids within aprt in substrate binding. It was also determined that, in contrast to UV, EMS did not appear to exhibit any strand bias in the distribution of mutations.

Evolutionary rate variation within Mus APRT.

Rodents are thought to have relatively high rates of evolution, twice as fast as the rates for mammals in other orders. However, the uniformly high rates of evolution inferred for the order Rodentia from Mus musculus and Rattus norvegicus are not consistently found for other rodent species. Using a maximum likelihood phylogenetic algorithm (DNAML), we show here that Mus spicilegus has a fivefold different rate of evolution in 1100 bp around the adenine phosphoribosyltransferase gene (APRT) since its divergence from a common ancestor with Mus musculus. A greater than threefold difference in rates is also found in a comparison of the number of evolutionary events directly detected from the APRT sequences of these two closely related Mus species. The evolutionary events can be directly detected, since M. spicilegus, M. musculus, and the four rodent outgroup species used to determine the ancestral sequence are so closely related. One of the major differences between M. spicilegus and M. musculus that might affect evolutionary rate is the degree of commensalism with man. The Mus species therefore provide a useful model for testing various hypotheses for the causes of rate variations between genes, and possibly, between lineages.

Enrichment for gene targeting in mammalian cells by inhibition of poly(ADP-ribosylation)

Inhibition of poly(ADP-ribosylation) reduces random genomic integration of transfected DNA and mildly stimulates intrachromosomal homologous recombination in mammalian cells. We investigated the effect of inhibition of poly(ADP-ribosylation) on the efficiency of gene targeting in Chinese hamster ovary (CHO) cell line ATS-49tg. This cell line is hemizygous for a defective adenine phosphoribosyltransferase (aprt) gene and is hypoxanthine phosphoribosyltransferase (hprt) deficient. Plasmid pAG100 contains a portion of the CHO aprt gene sufficient to correct the defect in ATS-49tg cells via gene targeting; pAG100 also contains an Escherichia coli guanine phosphoribosyltransferase (gpt) gene. Following transfection of ATS-49tg cells with pAG100, selection for gpt-positive transfectants allowed recovery of cells that had randomly integrated pAG100 while selection for aprt-positive cells allowed recovery of cells that had undergone gene targeting at the endogenous aprt locus. Treatment of cells with 3 mM 3-methoxybenzamide (3-MB), an inhibitor of poly(ADP-ribose) polymerase, decreased random integration and gene targeting of electroporated pAG100 about 5-fold. In contrast, treatment with 3 mM 3-MB during calcium phosphate transfection could reduce random integration more than 150-fold while reducing gene targeting less than two-fold. Therefore, as much as a 100-fold enrichment for gene targeting was achieved with calcium phosphate transfection.

Effects of Nonsense Mutations on Nuclear and Cytoplasmic Adenine Phosphoribosyltransferase RNA

We have analyzed Chinese hamster ovary (CHO) cell mutants bearing nonsense codons in four of the five exons of the adenine phosphoribosyltransferase (aprt) gene and have found a pattern of mRNA reduction similar to that seen in systems studied previously: a decrease in steady-state mRNA levels of 5- to 10-fold for mutations in exons 1, 2, and 4 but little effect for mutations in the 3'-most exon (exon 5). Nuclear aprt mRNA levels showed a similar decrease. Nonsense-containing aprt mRNA decayed at the same rate as wild-type mRNA in these cell lines after inhibition of transcription with actinomycin D. Nonsense-containing aprt mRNA is associated with polysomes, ruling out a model in which stable residual mRNA escapes degradation by avoiding translation initiation. A tetracycline-responsive form of the aprt gene was used to compare the stability of nonsense-containing and wild-type aprt mRNAs without globally inhibiting transcription. In contrast to measurements made in the presence of actinomycin D, after inhibition of aprt transcription with tetracycline, a nonsense-mediated destabilization of aprt mRNA was indeed demonstrable. The increased rate of decay of cytoplasmic aprt mRNA seen here could account for the nonsense-mediated reduction in steady-state levels of aprt mRNA. However, the low levels of nonsense-bearing aprt mRNA in the nucleus suggest a sensibility of mRNA to translation or translatability before it exits that compartment. Quantitation of the steady-state levels of transcripts containing introns revealed no accumulation of partially spliced aprt RNA and hence no indication of nonsense-mediated aberrancies in splicing. Our results are consistent with a model in which translation facilitates the export of mRNA through a nuclear pore. However, the mechanism of this intriguing nucleocytoplasmic communication remains to be determined.

The influence of a (GT)29 microsatellite sequence on homologous recombination in the hamster adenine phosphoribosyltransferase gene.

Several DNA sequence elements are thought to stimulate homologous recombination, illegitimate recombination, or both in mammalian cells. Some are implicated by their recurrence around rearrangement breakpoints, others by their effects on recombination of extrachromosomal plasmids. None of these sequences, however, has been tested on the chromosome in a defined context. In this paper we show how the adenine phosphoribosyltransferase locus in CHO cells can be used to study the recombinogenic potential of defined DNA sequences. As an example we have measured the effect on homologous recombination of a dinucleotide repeat, (GT)29, which has been shown to stimulate homologous recombination in extrachromosomal vectors 3-20 fold. On the chromosome at the adenine phosphoribosyltransferase locus, however, this sequence shows no capacity to stimulate recombination or to influence the distribution of recombination events.

Influence of alkyltransferase activity and chromosomal locus on mutational hotspots in Chinese hamster ovary cells.

High-density mutational spectra have been established for exon 3 of the gene encoding adenine phosphoribosyltransferase (APRT) of the Chinese hamster ovary (CHO) cell line derivative D422 and closely related and/or modified lines by using the mutagen ethyl methanesulfonate (EMS). The total number of selectable sites (GC-->AT transitions yielding a selectable APRT- phenotype) was estimated at 31 based on our own accumulated data base of 136 sequenced exon 3 mutations and on literature reports. D422 and two other APRT hemizygous lines each yielded very similar spectra and showed two populations of mutable sites: (i) 24 "baseline" sites that followed the Poisson distribution and therefore were equally susceptible to mutation and (ii) two hotspots, one comprising a cluster at nucleotides 1293-1309 and the other at nucleotide 1365. Collectively, the latter sites were about 10-fold more frequently mutated than the others. CHO cells are mer- as they lack the repair enzyme O6-methylguanidine methyltransferase (EC 2.1.1.63). In modified repair-proficient CHO cells, the distribution of mutations among all of the 31 sites was random, with only 3 of the 19 GC-->AT transitions in the above hotspots. To determine whether the distribution was locus-dependent, two independent lines carrying single copies of transfected APRT genes were generated from a derivative of D422 carrying a deletion in the endogenous APRT gene. Nucleotides 1293-1309 were again no longer preferentially mutated, but the site at nucleotide 1365 was still a hotspot. We conclude that mutational spectra in mer- cells are at least in part locus dependent and that some sequences are particularly susceptible to EMS mutagenesis and perhaps also to methyltransferase repair.

High-frequency illegitimate integration of transfected DNA at preintegrated target sites in a mammalian genome.

To examine the mechanisms of recombination governing the illegitimate integration of transfected DNA into a mammalian genome, we developed a cell system that selects for integration events in defined genomic regions. Cell lines with chromosomal copies of the 3' portion of the adenine phosphoribosyltransferase (APRT) gene (targets) were established. The 5' portion of the APRT gene, which has no homology to the integrated 3' portion, was then electroporated into the target cell lines, and selection for APRT gene function was applied. The reconstruction of the APRT gene was detected at frequencies ranging from less than 10(-7) to 10(-6) per electroporated cell. Twenty-seven junction sequences between the integrated 5' APRT and its chromosomal target were analyzed. They were found to be randomly distributed in a 2-kb region immediately in front of the 3' portion of the APRT gene. The junctions fell into two main classes: those with short homologies (microhomologies) and those with inserted DNA of uncertain origin. Three long inserts were shown to preexist elsewhere in the genome. Reconstructed cell lines were analyzed for rearrangements at the target site by Southern blotting; a variety of simple and complex rearrangements were detected. Similar analysis of individual clones of the parental cell lines revealed analogous types of rearrangement, indicating that the target sites are unstable. Given the high frequency of integration events at these sites, we speculate that transfected DNA may preferentially integrate at unstable mammalian loci. The results are discussed in relation to possible mechanisms of DNA integration.

High-efficiency triple-helix-mediated photo-cross-linking at a targeted site within a selectable mammalian gene.

Targeting damage to specific sites in the genome represents an attractive approach to manipulating gene function in mammalian cells. To test the applicability of triple-helix formation as a means for achieving precisely timed site-specific damage within a mammalian gene, a triplex-forming oligodeoxyribonucleotide (TFO) that binds with high affinity to a specific site within the hamster adenine phosphoribosyltransferase (APRT) gene was modified with the photochemically reactive psoralen derivative 4'-(hydroxymethyl)-4,5',8-trimethylpsoralen (HMT). The modified TFO, psorTFO1, bound with high affinity to a target site within intron 1 of the APRT gene. Upon irradiation, photomonoadducts (i.e., covalent adducts of psorTFO1 to one strand of the target duplex) were formed with high efficiency (approximately 50%). Introduction of 5'-TpA sequences (the preferred site for psoralen-induced photo-cross-links) at or near the triplex junction leads to increased efficiency of total photoadduct formation and to efficient formation of products that had the electrophoretic mobility on denaturing PAGE expected for three-stranded photo-cross-links (i.e., products containing psorTFO1 covalently linked to both strands of the duplex). Their identities as cross-links were verified by (1) identical electrophoretic mobility of products formed with either duplex strand radiolabeled and (2) coprecipitation of the radiolabeled duplex strand with its complementary biotinylated strand following denaturation. In addition, the cross-links were completely reversible upon irradiation at 254 nm, as expected for psoralen-mediated cross-links. The yield and distribution of photoadducts depended on 5'-TpA position. The most efficient photoadduct formation (approximately 90%) and photo-cross-link formation (approximately 90% of total photoadducts) were observed for a 5'-TpA adjacent to the triplex junction, with significant, but lower, cross-linking efficiency within three base pairs of the junction. Molecular models of the psoralen-conjugated triplex with its six-carbon linker suggested a simple explanation for this distance dependence: facile intercalation near the triplex/duplex junction, with increasing strain required for intercalation at more distant sites. These results indicate that psorTFO1 allows for DNA damage with high precision and high efficiency, and the likely proportion of monoadducts and cross-links can be estimated from the target sequence.

Identification and application of polymorphisms flanking the human adenine phosphoribosyltransferase gene

Human MutationVolume 8, Issue 3 p. 214-215 Short Communication Identification and application of polymorphisms flanking the human adenine phosphoribosyltransferase gene Simeon A. Boyadjiev, Corresponding Author Simeon A. Boyadjiev Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Simeon A. Boyadjiev, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Amrik Sahota, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251Search for more papers by this authorAmrik Sahota, Corresponding Author Amrik Sahota Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Simeon A. Boyadjiev, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Amrik Sahota, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251Search for more papers by this authorJay A. Tischfield, Jay A. Tischfield Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251Search for more papers by this author Simeon A. Boyadjiev, Corresponding Author Simeon A. Boyadjiev Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Simeon A. Boyadjiev, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Amrik Sahota, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251Search for more papers by this authorAmrik Sahota, Corresponding Author Amrik Sahota Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Simeon A. Boyadjiev, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251 Amrik Sahota, Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251Search for more papers by this authorJay A. Tischfield, Jay A. Tischfield Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202-5251Search for more papers by this author First published: 1996 https://doi.org/10.1002/(SICI)1098-1004(1996)8:3<214::AID-HUMU3>3.0.CO;2-9Citations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume8, Issue31996Pages 214-215 RelatedInformation