Constitutive expression of a 2',5'-oligoadenylate synthetase cDNA results in increased antiviral activity and growth suppression

The interferon (IFN)-induced enzyme 2',5'-oligoadenylate (2-5A) synthetase has been implicated in the development of antiviral activity in human and animal cells. However, its role in IFN-mediated growth inhibition remains unclear. To elucidate the function of 2-5A synthetase, we have stably introduced a human 2-5A synthetase cDNA into a human glioblastoma cell line (T98G). Constitutive expression of the cDNA in these cells is associated with increased levels of resistance to infection by encephalomyocarditis virus. One transfected subclone, which expresses elevated levels of 2-5A synthetase enzyme activity, also shows a reduced rate of cellular proliferation.

A family showing no evidence of linkage between the ataxia telangiectasia gene and chromosome 11q22-23

We have studied an inbred family in which two cousins presented with the same clinical features of ataxia telangiectasia (AT). Both patients are still ambulatory at ages 25 and 20. Cellular features of both patients are typical of AT and include increased radiosensitivity and an increased level of spontaneously occurring chromosome aberrations in peripheral blood lymphocytes. Linkage studies and haplotype analysis show no clear evidence that the gene for AT in this family is on chromosome 11q22-23. As previously reported AT families from complementation groups AB, C, and D have all shown linkage to this region of 11q22-23. Our study is of importance in suggesting additional locus heterogeneity.

Diagnosis of Duchenne and Becker muscular dystrophies by polymerase chain reaction. A multicenter study

OBJECTIVE--To assess the efficiency, reliability, and ease of use of DNA diagnosis for Duchenne and Becker muscular dystrophies (DMD/BMD) using the polymerase chain reaction (PCR). DESIGN--DNA from the patients was screened for deletion mutations using multiplex PCR, and the results were compared with those obtained by Southern blot analysis. The PCR multiplex reaction detects nine specific "hot-spot" exons in the dystrophin gene while the Southern analysis detects 66 specific dystrophin gene restriction fragments. The multiplex reaction requires 50-fold less DNA than Southern analysis and thus is considerably more sensitive. SETTING--Fourteen university-affiliated and private genetic disease diagnostic laboratories. PATIENTS--Male patients with clinical signs of DMD/BMD. Cases were selected for analysis randomly, without knowledge of whether a deletion was present within the dystrophin gene. MAIN OUTCOME MEASURES--The percentage of cases that were detectable by multiplex PCR in comparison with Southern analysis, the frequency, extent, and location of the detected deletion mutations. In some cases, duplication mutations were monitored. RESULTS--The accuracy of a single PCR multiplex amplification (nine exons) was compared with Southern analysis with 10 cDNA probes that cover the full length of the gene. The multiplex PCR analytic method detected 82% of those deletions detected by Southern analysis methods. In one of 745 analyses, the multiplex method suggested a single exon deletion, which was not confirmed by Southern analysis, representing a false-positive rate of 0.013%. CONCLUSIONS--Multiplex PCR represents a sensitive and accurate method for deletion detection of 46% of all cases of DMD/BMD. The method requires 1 day for analysis, is easy to perform, and does not use radioactive tracers. As such, multiplex PCR represents an efficient and rapid method for prenatal or postnatal diagnosis of DMD/BMD.

Monozygotic twins discordant for Aicardi syndrome

Aicardi syndrome is a developmental disorder characterised by agenesis of the corpus callosum, retinal lacunae, seizures, and developmental delay. It is believed to be X linked with lethality in males. We report a set of monozygotic female twins one of whom is healthy and intellectually normal while the other has the classical Aicardi phenotype with profound retardation. Family history is negative. Both had normal karyotypes. Monozygosity was established by blood grouping, chromosomal heteromorphisms, and DNA analysis using six hypervariable probes (five autosomal and one X linked) and three X linked RFLP probes. We tested the hypothesis that preferential inactivation of a different X chromosome had occurred in each girl. Methylation sensitive RFLP analysis of DNA from EBV transformed B lymphocytes and cultured skin fibroblasts using MspI/HpaII digestion and probing with M27 beta showed a very similar pattern of X inactivation in both twins with no evidence of preferential expression of one particular X chromosome. We conclude that the abnormalities in the affected twin are probably the consequence of a postzygotic mutation in early embryonic development.

X inactivation patterns in female monozygotic twins and their families

X inactivation studies have been carried out on 22 pairs of female monozygotic twins, one set of female monozygotic triplets, and their mothers and singleton sisters, using the probe M27 beta. Forty-eight per cent of the twins, 55% of their mothers, and 42% of their singleton sisters showed skewed X inactivation. Two of the triplets and their mother had random X inactivation, while the third triplet showed skewed X inactivation. Their singleton sister was homozygous with M27 beta. Of the twins, six pairs showed skewed X inactivation in favour of the same X chromosome, one pair showed skewed X inactivation favouring opposite X chromosomes, in seven pairs one twin showed skewed X inactivation while her co-twin showed random X inactivation, and in eight pairs both twins were random. A higher frequency of skewed pattern of X inactivation was not observed in the monozygotic twins when compared to a series of non-twin females (mothers and singleton sisters) and, so, the results in this study do not lend support to the theory that skewed X inactivation predisposes to the twinning process.

Hypodontia: genotype or environment? A case report of monozygotic twins

A case report is presented of monozygotic twins with variable expression of hypodontia. DNA fingerprinting was used to confirm monozygosity, and this evidence supports the theory that genetic coding is not the sole controlling factor in tooth agenesis. It is suggested that DNA fingerprinting should be considered the gold standard for determination of monozygosity.