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S Collyer

Publications and source records attributed to S Collyer.

16 recordsLinked to original sources
PubMed1992

A comparison between colour and luminance contrast in a spatial linking task.

We report experiments which compare the ability of subjects to employ colour vs luminance contrast as a basis for discriminating the degree of collinearity of random element string pairs. The purpose of the study was to determine the extent to which spatial integration mechanisms could utilize colour contrast. In order to probe directly the processes of spatial integration per se, it was necessary to control for any differences in the efficiency with which the visual system utilized colour and luminance contrast to locate the positions of the individual elements in the test stimuli. To do this we first established the "equivalent" luminance contrast of an isochromatic stimulus which produced equal performance to an isoluminant stimulus in a 2 element per string alignment task. This equated the colour defined and luminance defined stimuli for local positional acuity. We then measured performance for both isoluminant and equivalent luminance contrast stimuli for strings consisting of 2, 4, 8 and 16 elements. This tested for any differences in the processes of spatial integration. For both unmasked stimuli and stimuli embedded in luminance noise, there was no consistent trend favouring either luminance or colour contrast as the number of elements in the stimuli was increased. We conclude that the visual system is able to employ colour contrast as efficiently as luminance contrast for collinearity judgements, thus implicating a general role for colour vision in spatial integration tasks.

Color Perception↗
PubMed1988

Klinefelter's syndrome: an analysis of the origin of the additional sex chromosome using molecular probes.

The results of our study of the origin of the additional X chromosome in 39 males with a 47,XXY chromosome constitution are reported. We used a total of 20 X-linked RFLPs and successfully determined the origin of all 32 patients in whom DNA from both parents was available, and a further 3 in whom DNA was available from the patient and mother only. Males whose additional X chromosome was maternal in origin were further investigated using an X-linked centromere specific probe to determine the cell division at which the error occurred. Our results showed 53% of the non-disjunction to be attributable to pat mei I errors, 34% to mat mei I errors, 9% to mat mei II errors and 3% to a post-zygotic mitotic error. In the great majority of patients resulting from an error of maternal meiosis there was clear evidence of recombination involving the non-disjoined chromosomes, suggesting that absence of recombination is not an important aetiological factor in non-disjunction of the X chromosome in female meiosis. There was no alteration of parental age associated with the paternally derived 47,XXY males but a marked increase in maternal age among the maternally derived 47,XXY males, the increase being associated with mat mei I but not mat mei II errors. The proportion of paternally and maternally derived cases was similar among different ascertainment classes, suggesting that there is no dramatic effect of parental origin of the additional X chromosome on the phenotype of 47,XXY males.

Age Factors↗
PubMed1987

Mortality and causes of death in females with extra X chromosomes and males with extra Y chromosomes.

A prospective study of mortality in females with extra X chromosomes and males with extra Y chromosomes is reported. Among the 94 females who survived infancy and were then observed on average for 16 years there were 24 deaths compared with an expected mortality of 10.7. The greater than twofold increase is highly significant (p less than 0.005). The deaths were due to a variety of diseases but no significant increase from any single cause could be identified. Among 136 males with extra Y chromosomes observed on average for 12 years there were 10 deaths. This number is not significantly greater than the expected 6.4. No increase in mortality from a single cause was observed.

Adolescent↗
PubMed1986

Segregation analysis of balanced pericentric inversions in pedigree data.

The results of the recent European collaborative prenatal study suggested a segregation distortion of balanced pericentric inversions from carrier fathers but not carrier mothers (Boué & Gallano 1984). In an attempt to confirm these unexpected results, we examined 216 pedigrees with balanced pericentric inversions collected from three centers and from the literature. We were unable to detect any significant deviation from the expected 1:1 segregation of balanced pericentric inversions to normal karyotypes among the offspring of either carrier parent. To clarify the discrepancy between the studies, we reanalyzed the data from the prenatal study using all karyotyped individuals and, assuming conventional ascertainment rules, found a normal segregation pattern. We conclude that balanced pericentric inversions segregate normally in both males and females and that some retrospectively selected pedigrees were included as prospective in the prenatal study and this misclassification caused the apparent segregation distortion from carrier fathers.

Chromosome Inversion↗
PubMed1986

Mortality ratios, life expectancy, and causes of death in patients with Turner's syndrome.

In a prospective study of 156 female patients with Turner's syndrome who had survived infancy and been followed up for an average of 17 years there were 15 deaths. The expected mortality was 3.6. Sixteen of the patients had a congenital heart anomaly and five of the deaths occurred in this group. The 10 deaths in the remaining 140 were three times as many as expected. The reduction in life expectation was 12.5 years at age 1 year, 11 years at age 20, and 10 years at age 40. Deaths were due to a broad spectrum of diseases. In the sample as a whole there were eight deaths from diseases of the circulatory system. This number is significantly greater than expected, but four were due to congenital heart disease. When patients with congenital heart disease were omitted from the sample the mortality from circulatory disorders was not significantly increased. Within the category of circulatory disorders there were three deaths from dissection of the aorta, a number which is greatly in excess of the expected. Two of these patients had no previous evidence of heart disease.

Female↗
PubMed1985

Mortality ratios and life expectancy in X chromatin positive males.

In a prospective study of 466 X chromatin positive males an increase in mortality of about 50% has been observed. The increase is associated with a loss of about five years in life span. There is no convincing evidence that the increase is concentrated at any particular age group but this possibility could not be excluded. No effect of mode of ascertainment could be demonstrated. From this study we conclude that it is likely that the mortality experienced by chromatin positive males in general is at least 115% of that experienced by normal men and could be more than 200%.

Adolescent↗
PubMed1985

Causes of death in X chromatin positive males (Klinefelter's syndrome).

The causes of death in 466 X chromatin positive males (Klinefelter's syndrome) studied prospectively over the last 25 years have been analysed. We have previously reported the overall mortality to be increased by 50% and life expectancy reduced by about five years. A highly significant increase in mortality from cerebrovascular disease was observed in the sub group considered to be most representative of X chromatin positive males in general. In the age group up to 45 years this increase could be attributed to deaths from subarachnoid haemorrhage. An increase in mortality from respiratory diseases was observed in those ascertained in psychiatric hospitals. In the sample as a whole there were small but highly significant numbers of deaths from carcinoma of the breast and aortic valve disease. The deaths from carcinoma of the breast were comparable with those expected if female mortality rates were applied.

Adolescent↗
PubMed1984

An aetiological study of 290 XXY males, with special reference to the role of paternal age.

Data on 290 non-mosaic 47,XXY males have been analysed for possible associations with parental ages at birth, season of birth, sex ratio among sibs, and twinning. Comparison with matched population controls revealed a highly significant association with parental age, which was fully explained by dependence on maternal age and maternal age alone. The maternal age effect was determined with greater precision than in an earlier study of the same material, in which siblings were used as controls, and was estimated to result in an increased risk of between 5% and 10% per annum (p.a.). The estimated independent effect of paternal age, after fitting maternal age, was marginally (but not significantly) negative, and excluded an increased risk in excess of 3% p.a. Paternal age therefore appears to have little if any independent significance in the aetiology of 47,XXY. After correcting for seasonal variations in the population birth rate and smoothing, there was a peak of XXY births in March and a trough in November. Though not statistically significant, the pattern resembled that reported in previous studies, and was similar for both younger and older mothers. The twinning rate for both the XXYs and their sibs, and the sex ratio among the latter, were close to the corresponding population values.

Female↗
PubMed1982

The effect of variant chromosomes on reproductive fitness in man.

Reproductive fitness of carriers of heterochromatic variants of the human karyotype was found to be normal. The method was based on a comparison between known carriers and known non-carriers from the same pedigree in respect of live births, generation time and survival of offspring to reproductive age. A subset of the data had been included in an earlier study in which reproductive fitness of carriers was found to be significantly reduced. Our analysis suggests that the result may have been fortuitous, since it was not supported by the additional data. There was no evidence of heterogeneity between carriers of different types of variant or of different sex. There were indications of increased fetal losses to carriers, but the number of spontaneous abortions was insufficient to produce a detectable effect on gross reproductive fitness.

Abortion, Spontaneous↗
PubMed1982

A study of familial factors in Alzheimer's disease.

Data on the families of 74 probands with autopsy-proven Alzheimer's disease did not support the hypothesis, advanced by Heston and co-workers, of a familial association between Alzheimer's disease, Down's syndrome and immunoproliferative disorders. However, there are difficulties of interpreting negative conclusions in this type of study, particularly those resulting from small sample size and the impossibility of tracing all relatives; only the data for immunoproliferative disorders are incompatible with the hypothesis, those for Down's syndrome being too few to be informative. The incidence of presenile dementia among the first-degree relatives of probands was raised, as in many previous studies, and was consistent with a simple polygenic model. The mean parental age at birth of the probands was significantly raised by about 2 years (P divided by 0.01), but so also was that of their unaffected sibs, suggesting that the mechanism differs from that occurring in trisomy 21 and certain other aneuploidies.

Adolescent↗
PubMed1981

Phenotypically normal individuals with an inversion (X) (p22q13) and the recombinant (X), dup q.

Two families are described in which there is an inv(X) (p22q13) which has been transmitted for three generations. In one family (K482), no recombinants have been recovered and the inversion can be traced to a female born in 1839. In the second family (K491), a recombinant (X), dup q, has been recovered in a normal fertile woman. In both families the inverted X appears to be carrying the Xg allele. Despite extensive family studies no common ancestor has been found for the two families. The pattern of DNA synthesis has been studied in those individuals who are karyotypically 46,X,inv(X) (p22q13) and 46,X,rec(X)dup 1, inv(X) (p22q13); the selection of the abnormal as the late synthesizing X chromosome is random in the former and total in the latter. In some cells the two long arms of the recombinant X chromosome showed asynchrony of DNA replication.

Adult↗
PubMed1980

A collaborative study of the aetiology of Turner syndrome.

Data on Turner Syndrome from four sources were analysed for possible associations with several aetiological factors. Two classes of liveborn propositae were included, those with a non-mosaic 45, X karyotype (XO) and those with an isochromosome of the long arm of the X (iso-X). The numbers were 288 and 84 respectively and constitute the largest series of such cases to be analysed to date. For the XO's, an analysis using the liveborn full sibs of propositae as controls (method of Carothers et al. 1978) confirmed earlier studies in finding no positive association with parental age or birth order, and even suggested a small negative association. There were no significant differences between the mean parental ages of those cases shown by Xg grouping to have received a maternal X chromosome and those of the remainder. Among the iso-X's there was an exceptionally high proportion (17.5%) of parents with an age difference (paternal-maternal) of 10 or more years, raising the possibility of a paternal age effect. This agrees with earlier studies but conflicts with the finding of a negligible tendency for affected individuals to be born later within their sibships. The apparent discrepancy may be due to the relative insensitivity of the latter method to small parental age effects in samples of this size. For the XO's there were no detectable seasonal variations in the month of birth, but for the iso-X's there was a significant excess of births in the first 6 months of the year. Reviewing the conflicting evidence from the literature on seasonal variations in chromosomal aberrations, we urge caution in interpreting these results. In agreement with earlier studies, the incidence of twins among both XO's and iso-X's was higher than the population average, but the numbers were too small for statistical significance. There was no evidence for any alteration in the sex ratio among the liveborn sibs of either class.

Adolescent↗