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S L Sherman

Publications and source records attributed to S L Sherman.

At least 73 records · Page 4Linked to original sources
PubMed1991

Trisomy 21: association between reduced recombination and nondisjunction.

To assess the association between recombination and nondisjunction of chromosome 21, we analyzed cytogenetic and DNA markers in 104 trisomy 21 individuals and their parents. Our DNA marker studies of parental origin were informative in 100 cases, with the overwhelming majority (94) being maternal in origin. This value is significantly higher than the 75%-80% maternal nondisjunction rate typically observed in cytogenetic studies of trisomy 21 and illustrates the increased accuracy of the molecular approach. Using the maternally derived cases and probing at 19 polymorphic sites on chromosome 21, we created a genetic map that spans most of the long arm of chromosome 21. The map was significantly shorter than the normal female linkage map, indicating that absence of pairing and/or recombination contributes to nondisjunction in a substantial proportion of cases of trisomy 21.

Adult↗
PubMed1991

XY chromosome nondisjunction in man is associated with diminished recombination in the pseudoautosomal region.

To assess the possible association between aberrant recombination and XY chromosome nondisjunction, we compared pseudoautosomal region recombination rates in male meiosis resulting in 47,XXY offspring with those resulting in 46,XY and 46,XX offspring. Forty-one paternally derived 47,XXYs and their parents were tested at six polymorphic loci spanning the pseudoautosomal region. We were able to detect crossing-over in only six of 39 cases informative for the telomeric DXYS14/DXYS20 locus. Subsequently, we used the data to generate a genetic linkage map of the pseudoautosomal region and found it to be significantly shorter than the normal male map of the region. From these analyses we conclude that most paternally derived 47,XXYs result from meiosis in which the X and Y chromosomes did not recombine.

Chromosome Mapping↗
PubMed1988

Recurrence risks for relatives in families with an isolated case of the fragile X syndrome.

The proportion of sporadic cases among affected males with fragile X-related mental impairment was reinvestigated in a new sample of family data and compared to previous studies. It was found that the estimate has increased over time from 0 in the original study to 0.24 in the present study. This difference indicated that the correction used for the ascertainment of families in the original study may not have been adequate and that the suggestion that all mothers of affected males are obligate carriers may be wrong. Based on this new information, recurrence risks for relatives in a family with an isolated case of the fragile X or Martin-Bell syndrome were calculated under different assumptions in order to investigate the effect of 1) the knowledge of the phenotype of ancestors of the proband, 2) the dependence of expression of the mutation on the sex of the carrier parent, 3) the value of the penetrance of mental impairment (MI), and 4) the equality of mutation rates in egg and sperm. The assumptions made for modelling the mutational process had the greatest effect on the recurrence risk in sibs of an isolated case, whereas small differences in penetrance parameters and assumptions based on whether the ancestors were known to be normal or of unknown phenotype made little difference. Recurrence risks for the sibs and first cousins of an isolated case calculated under different assumptions are presented.

Female↗
PubMed1988

The longitudinal effects of growth on the Wits appraisal.

The longitudinal changes occurring between the ages of 4 and 24 years in the Wits appraisal and its component parts were evaluated in 40 persons. Contrary to what may have been believed previously, the Wits appraisal was not found to remain stable throughout the growth period. When the findings of the Wits appraisal were studied in individual subjects, there was a wide range of variation. Real changes in the Wits appraisal were found to be disguised clinically by the differential sagittal growth of pogonion in relation to B point, especially in male subjects. Furthermore, the appraisal was found to be affected profoundly by changes occurring in the angulation of the occlusal plane. It was concluded that if the Wits appraisal is to be used, it should be used in conjunction with other methods of assessment of apical base discrepancies and with due regard for the likely effects of changes in its component parts.

Adolescent↗
PubMed1988

Genetic mapping of the 21-hydroxylase locus: estimation of small recombination frequencies.

The locus for 21-hydroxylase (CA21HB) has been mapped to the interval between the HLA-B and HLA-DR loci on chromosome 6. Several methods of estimating genetic distance were used to determine whether CA21HB is closer to HLA-B or HLA-DR based on data collected on 157 families ascertained through a proband with the classical form of 21-hydroxylase deficiency (CA12Hd). The results were inconclusive but serve to highlight the limitations of present methods of estimating genetic distance when recombination frequencies are of the order of .005.

Chromosome Mapping↗
PubMed1988

A segregation and linkage study of classical and nonclassical 21-hydroxylase deficiency.

The segregation of classical and nonclassical 21-hydroxylase deficiency (21-OHD) and its linkage to HLA-B was investigated in 220 families. First, the surprisingly high frequency of the nonclassical 21-OHD gene estimated elsewhere was confirmed using a different methodology which avoided particular assumptions concerning the classification of an individual's genotype. In the present study the gene frequency was found to be .103 +/- .020 in an ethnically pooled sample and was as high as .223 +/- .062 among Ashkenazi Jews. Second, the segregation analysis of families ascertained through a nonclassical 21-OHD proband and those ascertained through a classical 21-OHD proband showed essentially identical results. A partial recessive model with no recombination between 21-OHD and HLA-B fitted the data better than did a complete recessive model with approximately 0.5% recombination between 21-OHD and HLA-B. The support for the partial over the complete recessive model depended on the assumed ascertainment probability, an unknown parameter in these data. Four families provided most of the evidence against the complete recessive model. All these included an unaffected sib who shared both HLA-B specificities in common with the affected proband. Possible explanations for the condition in these families include recombination, gene conversion, mutation in one of the parental gametes, or technical errors.

Adrenal Hyperplasia, Congenital↗
PubMed1987

Hypothesis regarding the nature of the fragile X mutation. A reply to Winter and Pembrey.

Pembrey et al. (1985) proposed a hypothesis regarding the nature of the fragile X [fra(X)] mutation. Recently they analyzed DNA linkage data (Winter and Pembrey 1986) that we and others have published on fra(X) pedigrees, found significant linkage heterogeneity, and modified their hypothesis to explain the observations. We would like to point out that their modified hypothesis is not supported by the data available.

Fragile X Syndrome↗