PAP: detection of ultra rare mutations depends on P* oligonucleotides: "sleeping beauties" awakened by the kiss of pyrophosphorolysis

A Longitudinal Case Study of Concurrent Infection with Syphilis and Human Immunodeficiency Virus During the Early Phase

Due to the low incidence of concurrent human immunodeficiency virus (HIV) and syphilis infection identified during the early phase, such as window period (WP), little is known about the clinical manifestations, diagnosis, and treatment efficacy at very early stages. One longitudinal study was conducted in a 42-year-old blood donor who was concurrently infected with syphilis and HIV. This blood donor was treated with a penicillin-based regimen and early antiretroviral therapy (ART). Sequential serological and nucleic acid tests were performed and the results were comparatively analyzed. A regular male donor who had two occasions of high-risk sexual behaviors 41 and 35 days before donation donated whole blood at the Shenzhen Blood Center. ART was initiated at the 28th day after donation (DAD), and syphilis treatment was received at the 49th DAD. Microbiological analysis using a fourth-generation anti-HIV enzyme-linked immunosorbent assay (ELISA) (4th GAHE) and electro-chemiluminesent immunoassay indicated a positive signal at the 6th DAD, while a third-generation anti-HIV ELISA (3rd GAHE) showed positive at the 26th DAD. All nucleic acid testing (NAT) for HIV RNA were reactive except the minipool NAT of 6 pooled samples at 117th DAD. The HIV viral load declined more than 4-log in copies per milliliter over 3 months, until reaching nondetectable levels at 246th DAD. Nevertheless, HIV-1 DNA was still detectable at 403rd DAD. Among all methods utilized, anti-treponema pallidum ELISA detected syphilis infection at the earliest time. A successful serological response to syphilis treatment was reached around the 80th DAD. Concurrent infection with syphilis and HIV during early phases did not significantly change the sensitivity of reagents in detection nor alter the therapeutic efficacy for the treatment of both pathogens, but might result in delayed HIV serological WP.

Efficacy of early antiretroviral therapy 36 hours after HIV infection in one blood donor

BACKGROUND

Discrepancies can occur with the use of clinical human immunodeficiency virus (HIV) diagnostic reagents for the HIV window period (WP; time from RNA to antibody detection by diagnostic or blood screening assays). Antiretroviral therapy (ART) during acute HIV infection can impact HIV-specific antibodies, antigens, and DNA/RNA detection. In this study, an HIV WP blood donor who initiated ART was monitored, evaluating the immunological and nucleic acid testing (NAT) results for early ART and discussing the potential effects on blood safety.

STUDY DESIGN AND METHODS

This was a follow-up study of a HIV WP donor detected 36 hours after high-risk sexual behavior, who was subsequently treated with ART. Immunological and NAT methods were comparatively analyzed.

RESULTS

The 4th generation HIV serologic assays were positive at Day 11, and the 3rd generation domestic anti-HIV assay was positive at Day 33. Individual donation (ID) NAT and minipool (MP) NAT of six samples were reactive, but 12-sample MP-NAT was nonreactive. ART resulted in a slow decline of HIV RNA, but HIV DNA was still detected on Day 757.

CONCLUSION

After ART, ID-NAT was more sensitive than MP-NAT or serologic detection; however, HIV DNA detection was more sensitive, with DNA but not RNA persistently detectable.

Mass-spectrometry analysis of modifications at DNA termini induced by DNA polymerases

Non-natural nucleotide substrates are widely used in the enzymatic synthesis of modified DNA. The terminal activity of polymerases in the presence of modified nucleotides is an important, but poorly characterized, aspect of enzymatic DNA synthesis. Here, we studied different types of polymerase activity at sequence ends using extendable and non-extendable synthetic models in the presence of the Cy5-dUTP analog Y. In primer extension reactions with selected exonuclease-deficient polymerases, nucleotide Y appeared to be a preferential substrate for non-templated 3'-tailing, as determined by MALDI mass-spectrometry and gel-electrophoresis. This result was further confirmed by the 3'-tailing of a non-extendable hairpin oligonucleotide model. Additionally, DNA polymerases induce an exchange of the 3' terminal thymidine for a non-natural nucleotide via pyrophosphorolysis in the presence of inorganic pyrophosphate. In primer extension reactions, the proofreading polymerases Vent, Pfu, and Phusion did not support the synthesis of Y-modified primer strand. Nevertheless, Pfu and Phusion polymerases were shown to initiate terminal nucleotide exchange at the template. Unlike non-proofreading polymerases, these two enzymes recruit 3'-5' exonuclease functions to cleave the 3' terminal thymidine in the absence of pyrophosphate.

Artifactual mutations resulting from DNA lesions limit detection levels in ultrasensitive sequencing applications

The need in cancer research or evolutionary biology to detect rare mutations or variants present at very low frequencies (<10⁻⁵) poses an increasing demand on lowering the detection limits of available methods. Here we demonstrated that amplifiable DNA lesions introduce important error sources in ultrasensitive technologies such as single molecule PCR (smPCR) applications (e.g. droplet-digital PCR), or next-generation sequencing (NGS) based methods. Using templates with known amplifiable lesions (8-oxoguanine, deaminated 5-methylcytosine, uracil, and DNA heteroduplexes), we assessed with smPCR and duplex sequencing that templates with these lesions were amplified very efficiently by proofreading polymerases (except uracil), leading to G->T, and to a lesser extent, to unreported G->C substitutions at 8-oxoguanine lesions, and C->T transitions in amplified uracil containing templates. Long heat incubations common in many DNA extraction protocols significantly increased the number of G->T substitutions. Moreover, in ∼50-80% smPCR reactions we observed the random amplification preference of only one of both DNA strands explaining the known ‘PCR jackpot effect’, with the result that a lesion became indistinguishable from a true mutation or variant. Finally, we showed that artifactual mutations derived from uracil and 8-oxoguanine could be significantly reduced by DNA repair enzymes.

Setup of a Protocol of Molecular Diagnosis of β-Thalassemia Mutations in Tunisia using Denaturing High-Performance Liquid Chromatography (DHPLC)

BACKGROUNDS

β-Thalassemia is one of the most prevalent worldwide autosomal recessive disorders. It presents a great molecular heterogeneity resulting from more than 200 causative mutations in the β-globin gene. In Tunisia, β-thalassemia represents the most prevalent monogenic hemoglobin disorder with 2.21% of carriers. Efficient and reliable mutation-screening methods are essential in order to establish appropriate prevention programs for at risk couples. The aim of the present study is to develop an efficient method based on the denaturing high-performance liquid chromatography (DHPLC) in which the whole β-globin gene (HBB) is screened for mutations covering about 90% of the spectrum.

METHODS

We have performed the validation of a DHPLC assay for direct genotyping of 11 known β-thalassemia mutations in the Tunisian population.

RESULTS

DHPLC assay was established based on the analysis of 62 archival β-thalassemia samples previously genotyped then validated with full concordance on 50 tests with blind randomized samples previously genotyped with DNA sequencing and with 96% of consistency on 40 samples as a prospective study.

CONCLUSION

Compared to other genotyping techniques, the DHPLC method can meet the requirements of direct genotyping of known β-thalassemia mutations in Tunisia and to be applied as a powerful tool for the genetic screening of prenatal and postnatal individuals.

Modified Proofreading PCR for Detection of Point Mutations, Insertions and Deletions Using a ddNTP-Blocked Primer

The development of simple, accurate, rapid and cost-effective technologies for mutation detection is crucial to the early diagnosis and prevention of numerous genetic diseases, pharmacogenetics, and drug resistance. Proofreading PCR (PR-PCR) was developed for mutation detection in 1998 but is rarely applied due to its low efficiency in allele discrimination. Here we developed a modified PR-PCR method using a ddNTP-blocked primer and a mixture of DNA polymerases with and without the 3'-5' proofreading function. The ddNTP-blocked primer exhibited the best blocking efficiency to avoid nonspecific primer extension while the mixture of a tiny amount of high-fidelity DNA polymerase with a routine amount of Taq DNA polymerase provided the best discrimination and amplification effects. The modified PR-PCR method is quite capable of detecting various mutation types, including point mutations and insertions/deletions (indels), and allows discrimination amplification when the mismatch is located within the last eight nucleotides from the 3'-end of the ddNTP-blocked primer. The modified PR-PCR has a sensitivity of 1-5 × 10² copies and a selectivity of 5 × 10^-5 mutant among 10⁷ copies of wild-type DNA. It showed a 100% accuracy rate in the detection of P72R germ-line mutation in the TP53 gene among 60 clinical blood samples, and a high potential to detect rifampin-resistant mutations at low frequency in Mycobacterium tuberculosis using an adaptor and a fusion-blocked primer. These results suggest that the modified PR-PCR technique is effective in detection of various mutations or polymorphisms as a simple, sensitive and promising approach.

Real-time bidirectional pyrophosphorolysis-activated polymerization for quantitative detection of somatic mutations

Detection of somatic mutations for targeted therapy is increasingly used in clinical settings. However, due to the difficulties of detecting rare mutations in excess of wild-type DNA, current methods often lack high sensitivity, require multiple procedural steps, or fail to be quantitative. We developed real-time bidirectional pyrophosphorolysis-activated polymerization (real-time Bi-PAP) that allows quantitative detection of somatic mutations. We applied the method to quantify seven mutations at codons 12 and 13 in KRAS, and 2 mutations (L858R, and T790M) in EGFR in clinical samples. The real-time Bi-PAP could detect 0.01% mutation in the presence of 100 ng template DNA. Of the 34 samples from the colon cancer patients, real-time Bi-PAP detected 14 KRAS mutant samples whereas the traditional real-time allele-specific PCR missed two samples with mutation abundance <1% and DNA sequencing missed nine samples with mutation abundance <10%. The detection results of the two EGFR mutations in 45 non-small cell lung cancer samples further supported the applicability of the real-time Bi-PAP. The real-time Bi-PAP also proved to be more efficient than the real-time allele-specific PCR in the detection of templates prepared from formalin-fixed paraffin-embedded samples. Thus, real-time Bi-PAP can be used for rapid and accurate quantification of somatic mutations. This flexible approach could be widely used for somatic mutation detection in clinical settings.

Mrassf1a-pap, a novel methylation-based assay for the detection of cell-free fetal DNA in maternal plasma

OBJECTIVES

RASSF1A has been described to be differentially methylated between fetal and maternal DNA and can therefore be used as a universal sex-independent marker to confirm the presence of fetal sequences in maternal plasma. However, this requires highly sensitive methods. We have previously shown that Pyrophosphorolysis-activated Polymerization (PAP) is a highly sensitive technique that can be used in noninvasive prenatal diagnosis. In this study, we have used PAP in combination with bisulfite conversion to develop a new universal methylation-based assay for the detection of fetal methylated RASSF1A sequences in maternal plasma.

METHODS

Bisulfite sequencing was performed on maternal genomic (g)DNA and fetal gDNA from chorionic villi to determine differentially methylated regions in the RASSF1A gene using bisulfite specific PCR primers. Methylation specific primers for PAP were designed for the detection of fetal methylated RASSF1A sequences after bisulfite conversion and validated.

RESULTS

Serial dilutions of fetal gDNA in a background of maternal gDNA show a relative percentage of ~3% can be detected using this assay. Furthermore, fetal methylated RASSF1A sequences were detected both retrospectively as well as prospectively in all maternal plasma samples tested (n = 71). No methylated RASSF1A specific bands were observed in corresponding maternal gDNA. Specificity was further determined by testing anonymized plasma from non-pregnant females (n = 24) and males (n = 21). Also, no methylated RASSF1A sequences were detected here, showing this assay is very specific for methylated fetal DNA. Combining all samples and controls, we obtain an overall sensitivity and specificity of 100% (95% CI 98.4%-100%).

CONCLUSIONS

Our data demonstrate that using a combination of bisulfite conversion and PAP fetal methylated RASSF1A sequences can be detected with extreme sensitivity in a universal and sex-independent manner. Therefore, this assay could be of great value as an addition to current techniques used in noninvasive prenatal diagnostics.

Non-invasive prenatal diagnosis of beta-thalassemia and sickle-cell disease using pyrophosphorolysis-activated polymerization and melting curve analysis

OBJECTIVE

The aim of this study was to develop a pyrophosphorolysis-activated polymerization (PAP) assay for non-invasive prenatal diagnosis (NIPD) of β-thalassemia major and sickle-cell disease (SCD). PAP is able to detect mutations in free fetal DNA in a highly contaminating environment of maternal plasma DNA.

METHODS

Pyrophosphorolysis-activated polymerization primers were designed for 12 informative SNPs, genotyped by melting curve analysis (MCA) in both parents. The PAP assay was tested in a series of 13 plasma DNA samples collected from pregnant women. A retrospective NIPD was performed in a couple at risk for SCD.

RESULTS

All PAP reactions were optimized and able to detect <3% target gDNA in a background of >97% wildtype gDNA. In all 13 cases, the paternal allele was detected by PAP in maternal plasma at 10 to 18 weeks of gestation. For the couple at risk, PAP showed presence of the normal paternal SNP allele in maternal plasma, which was confirmed by results of the chorionic villus sampling analysis.

CONCLUSIONS

In contrast to other methods used for NIPD, the combined PAP and MCA analysis detecting the normal paternal allele is also applicable for couples at risk carrying the same mutation, provided that a previously born child is available for testing to determine the linkage to the paternal SNPs.

PAP-LMPCR: an improved, sequence-selective method for the in vivo analysis of transcription factor occupancy and chromatin fine structure

In vivo footprinting and ligation-mediated PCR (LMPCR) are well-established methods for the examination of the chromatin structure of eukaryotic genes. Here, we describe an improved method (pyrophosphorolysis activated polymerization LMPCR or PAP-LMPCR) that overcomes the shortfalls of previous methods by being capable of reading through sequences that up to now were refractory to this type of analysis. This includes dinucleotide repeat sequences or GC-rich regions. We also describe conditions capable of distinguishing between different alleles, thus enabling the simultaneous analysis of monoallelically expressed genes without having to employ interspecies hybrids.

Mosaicism and haemophilia

Mosaicism may affect the haemophilia phenotype. Well-known instances include chromosomal mosaicism due to aneuploidy and pseudo-mosaicism due to varying patterns of X-chromosome inactivation. Chromosomal mosaicism in a chimera is a potential source of phenotypic variation. Gene mosaicism is commonplace. Its pattern and effect depend on the stage of development at which a mutation occurs. Proven or possible genetic mosaicism is an important consideration when predicting the likelihood of transmission of haemophilia to a future generation.

Analysis of cancer mutation signatures in blood by a novel ultra-sensitive assay: monitoring of therapy or recurrence in non-metastatic breast cancer

BACKGROUND

Tumor DNA has been shown to be present both in circulating tumor cells in blood and as fragments in the plasma of metastatic cancer patients. The identification of ultra-rare tumor-specific mutations in blood would be the ultimate marker to measure efficacy of cancer therapy and/or early recurrence. Herein we present a method for detecting microinsertions/deletions/indels (MIDIs) at ultra-high analytical selectivity. MIDIs comprise about 15% of mutations.

METHODS AND FINDINGS

We describe MIDI-Activated Pyrophosphorolysis (MAP), a method of ultra-high analytical selectivity for detecting MIDIs. The high analytical selectivity of MAP is putatively due to serial coupling of two rare events: heteroduplex slippage and mis-pyrophosphorolysis. MAP generally has an analytical selectivity of one mutant molecule per >1 billion wild type molecules and an analytical sensitivity of one mutant molecule per reaction. The analytical selectivity of MAP is about 100,000-fold better than that of our previously described method of Pyrophosphorolysis Activated Polymerization-Allele specific amplification (PAP-A) for detecting MIDIs. The utility of this method is illustrated in two ways. 1) We demonstrate that two EGFR deletions commonly found in lung cancers are not present in tissue from four normal human lungs (10(7) copies of gDNA each) or in blood samples from 10 healthy individuals (10(7) copies of gDNA each). This is inconsistent, at least at an analytical sensitivity of 10(-7), with the hypotheses of (a) hypermutation or (b) strong selection of these growth factor-mutated cells during normal lung development leads to accumulation of pre-neoplastic cells with these EGFR mutations, which sometimes can lead to lung cancer in late adulthood. Moreover, MAP was used for large scale, high throughput "gene pool" analysis. No germline or early embryonic somatic mosaic mutation was detected (at a frequency of >0.3%) for the 15/18 bp EGFR deletion mutations in 6,400 individuals, suggesting that early embryonic EGFR somatic mutation is very rare, inconsistent with hypermutation or strong selection of these deletions in the embryo. 2) The second illustration of MAP utility is in personalized monitoring of therapy and early recurrence in cancer. Tumor-specific p53 mutations identified at diagnosis in the plasma of six patients with stage II and III breast cancer were undetectable after therapy in four women, consistent with clinical remission, and continued to be detected after treatment in two others, reflecting tumor progression.

CONCLUSIONS

MAP has an analytical selectivity of one part per billion for detection of MIDIs and an analytical sensitivity of one molecule. MAP provides a general tool for monitoring ultra-rare mutations in tissues and blood. As an example, we show that the personalized cancer signature in six out of six patients with non-metastatic breast cancer can be detected and that levels over time are correlated with the clinical course of disease.

Mutation detection by real-time PCR: a simple, robust and highly selective method

Background

Molecular tests for diagnosis of disease, particularly cancer, are gaining increased acceptance by physicians and their patients for disease prognosis and selection of treatment options. Gene expression profiles and genetic mutations are key parameters used for the molecular characterization of tumors. A variety of methods exist for mutation analysis but the development of assays with high selectivity tends to require a process of trial and error, and few are compatible with real-time PCR. We sought to develop a real-time PCR-based mutation assay methodology that successfully addresses these issues.

Methodology/Principal Findings

The method we describe is based on the widely used TaqMan® real-time PCR technology, and combines Allele-Specific PCR with a Blocking reagent (ASB-PCR) to suppress amplification of the wildype allele. ASB-PCR can be used for detection of germ line or somatic mutations in either DNA or RNA extracted from any type of tissue, including formalin-fixed paraffin-embedded tumor specimens. A set of reagent design rules was developed enabling sensitive and selective detection of single point substitutions, insertions, or deletions against a background of wild-type allele in thousand-fold or greater excess.

Conclusions/Significance

ASB-PCR is a simple and robust method for assaying single nucleotide mutations and polymorphisms within the widely used TaqMan® protocol for real time RT-PCR. The ASB-PCR design rules consistently produce highly selective mutation assays while obviating the need for redesign and optimization of the assay reagents. The method is compatible with formalin-fixed tissue and simultaneous analysis of gene expression by RT-PCR on the same plate. No proprietary reagents other than those for TaqMan chemistry are required, so the method can be performed in any research laboratory with real-time PCR capability.

Noninvasive prenatal diagnosis of aneuploidy using cell-free nucleic acids in maternal blood: promises and unanswered questions

The discovery of cell-free fetal (cff) DNA and RNA in the maternal circulation has driven developments in noninvasive prenatal diagnosis (NIPD) for the past decade. Detection of paternally derived alleles in cff DNA is becoming well established. Now much interest is focussing on NIPD of fetal chromosomal abnormalities, such as trisomy 21, which is a considerable challenge because this demands accurate quantitative measurements of the amounts of specific cff DNA or cff RNA sequences in maternal blood samples. Emerging strategies for distinguishing and quantifying the fetal nucleic acids in the maternal circulation promise continued development of the field, and pose a number of unanswered questions.

Rapid genotyping of known mutations and polymorphisms in beta-globin gene based on the DHPLC profile patterns of homoduplexes and heteroduplexes

BACKGROUND

Beta-thalassemia represents a great heterogeneity as over 200 mutations have been identified for the beta-globin gene responsible for this disease. A rapid genotyping test with high accuracy, selectivity, and reproducibility suitable for the determination of known mutations is needed for prenatal screening and post-natal diagnosis of this disease in clinical setting.

DESIGN AND METHODS

We have performed the validation of a DHPLC assay for direct genotyping of known causative mutations in beta-globin gene using the chromatographic pattern-based strategy under partially-denaturing conditions.

RESULTS

DHPLC assay was established based on the analysis of 795 DNA samples from a group of various genotypes for the 20 mutations and 8 polymorphisms in beta-globin gene then validated on 319 tests in a blind study. The results obtained with this assay were in concordance with the results obtained by DNA sequence analysis.

CONCLUSION

This simple method can meet the requirements of direct genotyping of known beta-thalassemia mutations and/or polymorphisms in the clinical setting for Chinese and in general as a model for other populations.

PAP-LMPCR for improved, allele-specific footprinting and automated chromatin fine structure analysis

The analysis of chromatin fine structure and transcription factor occupancy of differentially expressed genes by in vivo footprinting and ligation-mediated-PCR (LMPCR) is a powerful tool to understand the impact of chromatin on gene expression. However, as with all PCR-based techniques, the accuracy of the experiments has often been reduced by sequence similarities and the presence of GC-rich or repeat sequences, and some sequences are completely refractory to analysis. Here we describe a novel method, pyrophosphorolysis activated polymerization LMPCR or PAP-LMPCR, which is capable of generating accurate and reproducible footprints specific for individual alleles and can read through sequences previously not accessible for analysis. In addition, we have adapted this technique for automation, thus enabling the simultaneous and rapid analysis of chromatin structure at many different genes.

Y chromosome detection by Real Time PCR and pyrophosphorolysis-activated polymerisation using free fetal DNA isolated from maternal plasma

OBJECTIVES

To validate the use of Real Time PCR, a widely used technique that can detect very low levels of Y chromosomal sequence, and to assess the use of a highly sensitive PCR technique, pyrophosphorolysis-activated polymerisation (PAP), for fetal sex determination using free fetal DNA (ffDNA).

METHODS

The fetal sex was determined by Real Time PCR in 58 pregnancies using ffDNA isolated from maternal plasma. In parallel with the Real Time PCR experiments, the presence of Y chromosome sequence was also determined using PAP on 54 isolated ffDNA samples.

RESULTS

Both techniques detected Y chromosome sequence at very low levels with 98% specificity and 100% sensitivity (Real Time n = 44, PAP n = 54). Furthermore, the PAP technique was shown to be more robust than the Real Time PCR as none of the samples tested failed to meet the acceptance criteria. Combining the two techniques for male fetal sex detection from maternal blood plasma increases the sensitivity and specificity to 100% in this series.

CONCLUSIONS

This study shows that both Real Time PCR and PAP can be used for Y chromosome detection on ffDNA. Furthermore, by using PAP in combination with Real Time PCR more reliable early prenatal sexing can be performed using ffDNA.

Sensitive Detection of KIT D816V in Patients with Mastocytosis

Background: The 2447 A&gt;T pathogenic variation at codon 816 of exon 17 (D816V) in the KIT gene, occurring in systemic mastocytosis (SM), leads to constitutive activation of tyrosine kinase activity and confers resistance to the tyrosine kinase inhibitor imatinib mesylate. Thus detection of this variation in SM patients is important for determining treatment strategy, but because the population of malignant cells carrying this variation is often small relative to the normal cell population, standard molecular detection methods can be unsuccessful.

Methods: We developed 2 methods for detection of KIT D816V in SM patients. The first uses enriched sequencing of mutant alleles (ESMA) after BsmAI restriction enzyme digestion, and the second uses an allele-specific competitive blocker PCR (ACB-PCR) assay. We used these methods to assess 26 patients undergoing evaluation for SM, 13 of whom had SM meeting WHO classification criteria (before variation testing), and we compared the results with those obtained by direct sequencing.

Results: The sensitivities of the ESMA and the ACB-PCR assays were 1% and 0.1%, respectively. According to the ACB-PCR assay results, 65% (17/26) of patients were positive for D816V. Of the 17 positive cases, only 23.5% (4/17) were detected by direct sequencing. ESMA detected 2 additional exon 17 pathogenic variations, D816Y and D816N, but detected only 12 (70.5%) of the 17 D816V-positive cases. Overall, 100% (15/15) of the WHO-classified SM cases were codon 816 pathogenic variation positive.

Conclusion: These findings demonstrate that the ACB-PCR assay combined with ESMA is a rapid and highly sensitive approach for detection of KIT D816V in SM patients.

Approaches for analyzing human mutations and nucleotide sequence variation: a report from the Seventh International Mutation Detection meeting, 2003

The Seventh International Symposium on Mutations in the Human Genome, Mutation Detection 2003, was held during 2-6 July 2003 in Palm Cove near Cairns, Australia. The meeting was organized under the auspices of the Human Genome Organisation (HUGO) as a satellite meeting of the International World Congress of Genetics, held in Melbourne the following week. Meeting participants reported on advances in mutation detection technologies, including advances in high-throughput detection systems for SNP genotyping applicable to the international haplotype mapping project (HapMap); and bioinformatics tools, including databases for handling and processing growing amounts of genome variation data. This meeting report summarizes the presentations and cites related articles from the special issue of Human Mutation (Volume 23#5, May 2004; available online at www.wiley.com/humanmutation).