Detection of point mutations in amplified single copy genes by biotin-labelled oligonucleotides: diagnosis of variants of alpha-1-antitrypsin

The production of PCR products with 5' single-stranded tails using primers that incorporate novel phosphoramidite intermediates

We have prepared several novel phosphoramidites and have synthesised oligonucleotides incorporating them internally. The presence of these residues in an oligonucleotide template presents an impossible barrier to primed synthesis by Taq DNA polymerase. When extended as polymerase chain reaction products, these oligonucleotides no longer serve as templates for the polymerase beyond the insertion sites of the modified intermediates, thereby producing single-stranded tails on amplification products. These tails can then be used for solid phase capture and colorimetric detection of PCR products.

Cloning and characterization of the human sperm receptor ligand ZP3: evidence for a second polymorphic allele with a different frequency in the Caucasian and Japanese populations

The human ZP3 gene, encoding the glycoprotein responsible for sperm-egg recognition, has been cloned using mouse ZP3 DNA as a probe. Genomic and cDNA cloning revealed eight exons, spread over 18 kb, encoding a protein of 424 amino acids with a 67% homology to mouse and hamster ZP3. Southern blotting, gene cloning, and sequence analysis were used to show that ZP3 is not a single-copy gene and that the human genome contains a second polymorphic locus which, due to an extra G residue in exon 8, has the potential to encode a truncated protein of 372 amino acids. Direct sequence analysis of polymerase chain reaction-amplified exon 8 DNA of 56 individuals of various human populations revealed three different sequence patterns: one containing only ZP3-424-coding sequences and two containing ZP3-424- and ZP3-372-coding DNA. The distribution of these three sequence patterns is significantly different between the Caucasian and Japanese populations, as indicated by ZP3-372 allele frequencies of 69 and 21%, respectively. Isolation of ZP3-424 and ZP3-372 cDNAs suggests that both loci represent functional transcription units. Therefore, it is hypothesized that throughout the human population during oogenesis ZP3 is translated from mRNAs derived from two to four transcription units. Provided that ZP3-372 mRNA is translated in vivo, corresponding differences in ZP3-372 protein levels might have an impact on human zona pellucida composition.

Specific diagnosis of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency in dried blood spots by a polymerase chain reaction (PCR) assay detecting a point-mutation (G985) in the MCAD gene

The discovery of a point-mutation, adenine-to-guanine, at position 985 in the gene coding for MCAD (G985), gave the basis for an easy and specific polymerase chain reaction test. We tested the specificity of such a PCR based assay and detected correctly G985 and A985 in sequence verified cDNA clones. We showed that the G985 mutation is present in genomic DNA from 48 of 50 patients with confirmed MCAD deficiency, originating from various European countries, Australia and the USA. On the basis of this high frequency of the G985 mutation among patients, we improved and optimized the assay with respect to reliability and convenience for routine diagnostic and screening purposes. As little as 2 microliters blood from filter-paper blood-spots (Guthrie spots) is sufficient for the test.

Clinical applications of the polymerase chain reaction

The polymerase chain reaction (PCR) is a technique that allows a million-fold, or greater, amplification of defined regions of DNA or RNA. It is potentially capable of detecting a single copy of a gene, present only once in 105 eukaryotic cells. This remarkable level of sensitivity has allowed the development of many diagnostic assays for human pathogens and disease states. These include: the detection of viral, bacterial and protozoal agents; diagnosis and genetic analysis of inherited diseases such as β-thalassaemia, sickle cell disease, haemophilia, Tay-Sachs disease and many others; diagnosis and analysis of neoplastic disorders such as, chronic myelogenous leukaemia (CML), acute lymphocytic lymphoma (ALL), follicular lymphomas and various other cancers, including the detection of activated oncogenes; prenatal and pre-implantation diagnosis; and the development of genetic risk prediction.

The PCR can greatly simplify diagnostic processes that were previously difficult to perform, particularly where the initial amounts of biological material were very limited. In other cases, PCR provides the only method available for detection and diagnosis. However, although simple in theory, the PCR technique remains, for routine clinical diagnostic purposes, currently in the domain of the specialist laboratory. This is because of its sensitivity to nucleic acid contamination from other sources that can cause misleading results. Procedures and precautions are being developed to minimize this problem and there is little doubt that, in many instances, the PCR will be the diagnostic method of choice within the next few years.