H63D is an haemochromatosis associated allele.
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Genes, MHC Class I↗
Biomedical subjects
K Snow
Publications and source records attributed to K Snow.
Segregation of the fragile X mutation from a male with a full mutation: unusual somatic instability in the FMR-1 locus.
Fragile X syndrome is associated with an unstable CGG-repeat in the FMR-1 gene. There are few reports of affected males transmitting the FMR-1 gene to offspring. We report on a family in which the propositus and his twin sister each had a full mutation with abnormal methylation. Their mother had an FMR-1 allele in the normal range and a large premutation, with normal methylation. The maternal grandmother had two normal FMR-1 alleles. The maternal grandfather had an unusual somatic FMR-1 pattern, with allele size ranging from premutation to full mutation. No allele was detectable by PCR analysis. Multiple Southern blot analyses identified a hybridization pattern that originated at a distinct premutation band and extended into the full mutation range. Methylation studies revealed a mosaic pattern with both unmethylated premutations and methylated full mutations. This individual declined formal evaluation but did not finish high school and has difficulty in reading and writing. The size of the premutation FMR-1 allele passed to his daughter is larger than his most prominent premutation allele. This is most likely due to gonadal mosaicism similar to that in his peripheral lymphocytes. Alternatively, this expansion event may have occurred during his daughter's early embryonic development and this large premutation allele is mitotically unstable. This pattern of FMR-1 alleles in a presumably mildly affected male is highly unusual. These findings are consistent with the absence of transmission of a full fragile X mutation through an expressing male. Studies of tissue specific FMR-1 allele expansion and FMR-1 protein expression on this individual should help to determine the correlation of the molecular findings with the phenotypic effects.
Alleles↗
Molecular analysis of the Huntington's disease gene in New Zealand.
AIMS: To establish and validate a polymerase chain reaction (PCR)-based diagnostic test in New Zealand, which enables the number of CAG repeats present in the Huntington's disease (HD) gene to be determined with speed and accuracy. To develop procedures for reporting and counselling probands and families. METHODS: The analysis of the CAG repeat region in Huntington's disease and normal chromosomes involved PCR amplification of genomic DNA using either the incorporation of radioactive deoxynucleotides or fluorescent oligonucleotide primers. RESULTS: The molecular analysis of the CAG repeat sequence in the Huntington's disease gene of over 100 New Zealand individuals has been performed. Huntington's disease chromosomes contained 37-70 (median 44) repeats whereas normal chromosomes contained 9-27 (median 18) repeats. Six individuals from three families had an allele in the intermediate range (30-36 repeats). Instability of the CAG repeat upon transmission from generation to generation was also observed. A comparison of the results obtained using radioactive and fluorescent assays indicates that while both methods are reliable, the latter method is more rapid and allows for automation to be incorporated in the scoring of allele sizes. CONCLUSIONS: Our analysis of Huntington's disease alleles has shown a profile of CAG repeat lengths that is consistent with those reported internationally. In addition, reporting and counselling procedures have been established for presymptomatic testing of Huntington's disease in New Zealand.
DNA↗
Hyperoxia enhances expression of gamma-glutamyl transpeptidase and increases protein S-glutathiolation in rat lung.
By participating in glutathione (GSH) synthesis, gamma-glutamyl transpeptidase (GGT) influences the GSH redox cycle, which is a major contributor in protecting against reactive oxygen metabolites. This study determined the effect of prolonged exposure of neonatal rats to > 98% oxygen on expression of GGT and on GSH metabolism. Lungs of neonatal rats chronically exposed to hyperoxia had increased expression of GGT mRNA, resulting in significantly higher GGT protein levels and enzyme activity than in lungs of animals raised in room air. Hyperoxia also upregulated glucose-6-phosphate dehydrogenase, but Na-K-ATPase activity was not changed. GGT mRNA, protein level, and enzyme activity returned to control levels after recovery in room air for 3 days. Levels of GSH, glutathione disulfide, and protein-bound GSH (S-glutathiolated protein) rose with hyperoxia and fell during recovery. S-glutathiolation is likely a mechanism for protection and a regulatory modification of protein sulfhydryl groups. Hyperoxia-induced upregulation of GGT and the concomitant increase in protein S-glutathiolation appear to be additional components fundamental in protecting the lung against oxidative injury.
Animals↗
The fragile X premutation in carriers and its effect on mutation size in offspring.
The pattern of inheritance in the fragile X (fra(X)) mutation follows a multistage intergenerational process in which the premutation evolves into the full mutation and the characteristic phenotype of the fra(X) syndrome after passing through oogenesis or a postzygotic event. Findings from our multicenter study confirm a strong direct relationship between fra(X) premutation size in the mother and probability of a full mutation in offspring with the mutation. Remarkably, the best-fitting equations are nonlinear asymptotic functions. The close approximation to both the logistic model and Gompertz suggests a process of accumulation of errors in DNA synthesis, as has been proposed previously. We also note that a larger-than-expected number of daughters of transmitting males have premutations that are smaller than their fathers', and that proportion is significantly higher than the proportion of daughters whose premutations are smaller than their mothers'. Intergenerational decreases in premutation size have been reported in other trinucleotide-repeat disorders and also appear to be parent-of-origin specific. Thus, while intergenerational expansion to the full mutation in fra(X) may manifest a postzygotic event, decreases in mutation size may occur during or prior to meiosis.
Female↗
The gift of compassion.
Christmas Day in a hospital is always different from Christmas Day anywhere else. For one thing, there is a sense of isolation; family and friends are elsewhere and every patient who can be discharged, even temporarily, leaves for the day.
Accidents↗
Program for controlling the use of ondansetron injection.
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Clinical Protocols↗
High functioning fragile X males: demonstration of an unmethylated fully expanded FMR-1 mutation associated with protein expression.
Fragile X (fra(X)) males with a standardized IQ score of 70 or higher represent a high functioning (HF) or nonretarded fra(X) male group. This group, which does not include nonpenetrant males, has received little research attention to date. Of 221 fra(X) males who had been evaluated through The Children's Hospital in Denver since 1981 and had completed cognitive or developmental testing, 29 (13%) were high functioning by the above definition. We found that HF males on the whole had a lower cytogenetic score and were younger than retarded fra(X) males, but there was no difference between these two groups in the number of typical fra(X) physical manifestations present. FMR-1 DNA testing was performed on 134 fra(X) males and methylation status was determined for 51 of these. A greater percentage of HF males had a mosaic pattern or an incompletely methylated full mutation than did retarded males. A unique DNA pattern, an unmethylated fully expanded mutation, was discovered in 3 of the highest functioning fra(X) males. Protein studies performed on 2 of these males demonstrated the presence of FMR-1 protein, albeit at lower levels than normal. FMR-1 protein was not present in retarded fra(X) males. Significant FMR-1 protein expression may be responsible for higher cognitive functioning in the 2 males with unmethylated fully expanded mutations compared to retarded fra(X) males.
Adolescent↗
Reliability of diagnostic assessment of normal and premutation status in the fragile X syndrome using DNA testing.
Until recently, fragile X [fra(X)] syndrome was diagnosed by cytogenetic techniques and/or linkage analysis. Investigation of the mutation at the molecular level has shown that amplification of a polymorphic trinucleotide repeat (CGG) is diagnostic of this syndrome. Fu et al. [1991] observed that between 6-54 copies of the repeat were associated with alleles found in the general population, whereas 50-200 copies were associated with the premutation. In general, differences in copy number between the normal and premutated states are sufficiently large so that the probability of misclassification is, for all practical purposes, zero. However, there is a grey area in which members from both populations overlap. The purpose of our study was to determine the probability of misclassifying an individual from either the general or premutation population. DNA obtained from the general population and transmitting fra(X) females were analyzed from 3 centers in North America: Houston, Texas; Rochester, Minnesota; and Kingston, Ontario. The distribution of normal alleles from Houston was not significantly different from those obtained from Rochester. Therefore, these 2 samples were combined and the pooled distribution of normal alleles was compared with the pooled distribution of premutations. Results indicated that if 50 repeats were used as the cutoff criterion, sensitivity is 100%, specificity is 99.6%, and the probability that an individual has the fra(X) premutation given that the number of repeats is greater than 50 is 95%. Other cutoff criteria (45, 55, 60, 65) employed produced like findings, although 55 repeats appears to be a marginally superior criterion to 50. An independent sample from Kingston was used to verify the original assessments.(ABSTRACT TRUNCATED AT 250 WORDS)
Bayes Theorem↗
Heat shock does not induce tolerance to hyperoxia.
Thermal stress is associated with the induction of a specific set of proteins called heat shock proteins and with the induction of thermal tolerance. Heat stress has been shown to be capable of inducing at least partial tolerance to other stresses, including some oxidant stresses. Furthermore, these oxidant stresses are reported to be inducers of heat shock proteins. We hypothesized that hyperoxic stress would induce heat shock proteins and that factors induced by thermal stress, including heat shock proteins, would offer at least partial protection from hyperoxic exposure. We were particularly interested in a level of protection that would be relevant to clinical situations. Lung fibroblasts and live animals were exposed to thermal stress and/or hyperoxic stress and examined for induction of HSP70 (the most conserved of the heat shock proteins) and for induced tolerance as determined by the ability of cells to metabolize 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and by comparison of lung wet to dry weight ratios in live animals. Each stress induced tolerance to itself, but there was no evidence of heat stress inducing tolerance to hyperoxic stress. Furthermore, there was only minimal induction of HSP70 mRNA by hyperoxic exposure. We conclude that some overlap of mechanisms of induced tolerance by hyperoxic and thermal stress exists, but that differences far outweigh similarities.
Animals↗
Length of uninterrupted CGG repeats determines instability in the FMR1 gene.
Analysis of 84 human X chromosomes for the presence of interrupting AGG trinucleotides within the CGG repeat tract of the FMR1 gene revealed that most alleles possess two interspersed AGGs and that the longest tract of uninterrupted CGG repeats is usually found at the 3' end. Variation in the length of the repeat appears polar. Alleles containing between 34 and 55 repeats, with documented unstable transmissions, were shown to have lost one or both AGG interruptions. These comparisons define an instability threshold of 34-38 uninterrupted CGG repeats. Analysis of premutation alleles in Fragile X syndrome carriers reveals that 70% of these alleles contain a single AGG interruption. These data suggest that the loss of an AGG is an important mutational event in the generation of unstable alleles predisposed to the Fragile X syndrome.
Base Sequence↗
Sequence analysis of the fragile X trinucleotide repeat: implications for the origin of the fragile X mutation.
This study addresses mechanism of instability of the FMR-1 (CGG)n-repeat, and investigates features which may distinguish between normal stable and fragile X unstable repeats. To achieve this, we have sequenced 178 alleles to analyze patterns of AGG interruptions within the CGG repeat, and have typed the (CA)n-repeat at DXS548 for 204 chromosomes. Overall, our data is consistent with the idea that the length of uninterrupted CGG repeats determines instability. We predict that certain sequence configurations [no AGG, and (CGG)9-11AGG(CGG) > or = 20] present in the general population, are predisposed towards replication slippage. Association between these proposed predisposing repeats and DXS548 alleles may explain the previously reported frequencies of fragile X mutations and large-size normal repeats on specific haplotype backgrounds. We propose that predisposing alleles arise in the general population by as yet undefined mechanism(s) which introduce a relatively long stretch of pure CGG repeat at the 3'-end (relative to the direction of transcription) of the FMR-1 repeat region. The 3' pure repeat may then be susceptible to further expansion by replication slippage. Slippage on these predisposing chromosomes could accumulate over many generations until a threshold size is reached, at which point the repeat is susceptible to greater instability (i.e. premutation stage). Thus, results suggest that evolution of fragile X full mutations could involve 4 definable stages: 1) ancestral events leading to the formation of predisposing alleles which have large total repeat length (e.g. between 35 to 50) but no AGG or 1 AGG; 2) gradual slippage of these predisposing alleles to small premutations (S alleles); 3) conversion from S alleles to larger premutations (Z); 4) massive expansion from a Z allele to a full mutation (L).
Alleles↗
Is there a relationship between autoantibodies and silicone-gel implants?
The present study was conducted to determine if 200 patients with silicone-gel implants demonstrated elevated levels of autoantibodies, compared with a similar group of 100 age-matched control subjects without breast implants. These results were then compared with 29 patients who had demonstrated implant rupture. Differences in the frequency of autoantibody levels were determined by the chi-squared test. Differences in autoantibody titers were determined by Wilcoxon's signed rank test. Differences were considered significant with p > 0.05. The prevalence of a positive antinuclear antibody (ANA) test (dilution 1:100) in the 200 patients with breast implants was 26.5% compared with 28% in the 100 control subjects. In 29 patients with implant rupture, only 17.2% tested ANA positive. These values were not significantly different. In addition, there were no significant differences between the ANA titers of positive patients in each group. In each of the three groups, all patients who tested ANA positive were analyzed to assess the frequency and titer of other autoantibodies, including anti-DNA, anti-cardiolipin, anti-SSA, anti-SSB, anti-SM, anti-RNP, and anti-Scl-70. There were no significant differences between the frequency or titer of any of these autoantibody levels in each of the three groups of patients. These studies strengthen the concept that there is no conclusive evidence that silicone-gel implants are related to the development of connective tissue disease.
Adult↗
Doctors under the knife.
With Bill Clinton's new reforms only a month away, the health-care system is on the operating table--and the doctors are under the knife. Americans have a love-hate relationship with physicians: they like the care that doctors provide but hold them to blame for the nation's health-care mess. NEWSWEEK looks at how the culture of medicine may change, assesses doctors' fears--and examines the brave new world of HMOs.
American Medical Association↗
Molecular-clinical correlations in children and adults with fragile X syndrome.
INTRODUCTION: Fragile X syndrome is the most commonly known inherited form of mental retardation. The intellectual abilities range from a normal IQ with learning disabilities to severe mental retardation. In males, there is a tendency for IQ decline in childhood. The purpose of this study was to correlate variations of the molecular cytosine guanine guanine (CGG) amplification in the fragile X mental retardation-1 (FMR-1) gene with the clinical findings, including IQ and physical features. METHODS: Full-scale IQ and cytogenetic results in 116 individuals with the FMR-1 mutation were studied. The IQ testing was performed with age-appropriate standardized tests. Physical features were summarized in a physical index score for each patient. The FMR-1 results were determined with the OX1.9 probe and the following system was used: P1 indicates premutation; P2, large premutation to small full mutation; P3, full mutation; and P4, mosaic. RESULTS/CONCLUSIONS: The findings showed that those females with a small insert in the P1 range had a significantly higher IQ than other heterozygotes (P2, P3, and P4 categories). P4 males had a significantly higher IQ than P2 or P3 males. In cross-sectional age comparisons, the slope of the IQ decline was greater in P2 males than in P4 or P3 males.
Adolescent↗
The polymerase chain reaction. Applications in dermatology.
Within the space of the last 5 years, application of the revolutionary in vitro method of deoxyribonucleic acid (DNA) amplification known as the polymerase chain reaction (PCR), has become ubiquitous. The rapidly increasing number of clinical and research articles utilizing this technology, both in the dermatologic and general medical literature, requires one to have at least a basic understanding of how the PCR is conducted, what it has to offer, and the potential shortcomings. Such knowledge will hopefully allow a more critical appraisal of an increasingly complex literature. This review aims to describe the methodology and medical applications of this powerful technique with special consideration to the increasing role PCR may have on dermatologic research and practice.
Genetic Diseases, Inborn↗
Analysis of a CGG sequence at the FMR-1 locus in fragile X families and in the general population.
In this study, we have characterized a CGG repeat at the FMR-1 locus in more than 100 families (more than 500 individuals) presenting for fragile X testing and in 247 individuals from the general population. Both Southern blot and PCR-based assays were evaluated for their ability to detect premutations, full mutations, and variability in normal allele sizes. Among the Southern blot assays, the probes Ox1.9 or StB12.3 with a double restriction-enzyme digest were the most sensitive in detecting both small and large amplifications and, in addition, provided information on methylation of an adjacent CpG island. In the PCR-based assays, analysis of PCR products on denaturing DNA sequencing gels allowed the most accurate determination of CGG repeat number up to approximately 130 repeats. A combination of a Southern blot assay with a double digest and the PCR-sequencing-gel assay detected the spectrum of amplification-type mutations at the FMR-1 locus. In the patient population, a CGG repeat of 51 was the largest to be stably inherited, and a repeat of 57 was the smallest size of premutation to be unstably inherited. When premutations were transmitted by females, the size of repeat correlated with risk of expansion to a full mutation in the next generation. Full mutations (large repeats typically associated with an abnormal methylation pattern and mitotic instability) were associated with clinical and cytogenetic manifestations in males but not necessarily in females. In the control population, the CGG repeat ranged from 13 to 61, but 94% of alleles had fewer than 40 repeats. The most frequent allele (34%) was a repeat of 30. One female had an allele (61 repeats) within a range consistent with fragile X premutations, while two other individuals each had a repeat of 52. This suggests that the frequency of unstable alleles in the general population may be approximately 1%.
Blotting, Southern↗
Characterization of human sperm antigens and antisperm antibodies in infertile patients.
OBJECTIVE: To identify which sperm antigens may elicit the production of functionally important antisperm antibodies. DESIGN: Immunoblot analysis was performed on 69 serum and 9 seminal plasma samples from infertile patients, using detergent extracts of pooled donor sperm as the antigen source. Serum and seminal plasma had been previously tested by an indirect immunobead binding test (IBT); 61 IBT-positive and 17 IBT-negative samples were included in the study. Proteins recognized by IBT-positive but not IBT-negative samples were most likely to be cell surface antigens, whereas proteins recognized by both IBT-positive and IBT-negative samples were probably intracellular. Antibodies directed toward surface antigens would be most likely to affect fertilization. Characterization of sperm surface proteins on both acrosome-intact and -reacted sperm used labeling of cell surface proteins with an N-hydroxysuccinimide ester of biotin, fractionation of sperm heads and tails, and lectin binding to determine glycosylation. RESULTS: Specific immunoreactivity (with respect to IBT results) was observed to 35K, 40 to 45K, 57K, 66K, and 88 to 90K MW proteins. Characterization studies identified an 88K MW glycosylated plasma membrane protein, a 66K MW inner acrosomal membrane protein, a 34K MW inner acrosomal membrane protein, and a 35K MW prominent tail protein. CONCLUSION: Immunological infertility may involve several antigens characterized in this study. Further studies are necessary to determine if antibodies to these specific proteins interfere with sperm function.
Acrosome↗