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Biomedical subjects

G C Windham

Publications and source records attributed to G C Windham.

45 records · Page 3Linked to original sources
PubMed1984

Malformations in twins and their siblings, Norway, 1967-79.

During 1967-79 the population-based Medical Birth Registry of Norway registered 7,660 twin pairs (1% of births) born to 7,596 mothers, who gave birth to 6,608 additional infants (twin siblings). The total rate of malformations among twins (278.1/10,000) was not significantly different than among singletons (302.1/10,000), nor among twin siblings (314.8/10,000). By specific type of defect, twins had significantly higher rates than singletons of central nervous system (CNS) defects (Rate Ratio = 1.8) and cardiovascular defects (RR = 1.5). The twins also had a significantly low rate of congenital hip dislocation (RR = 0.4), which may explain the relatively low incidence of malformations in twins. Like-sex (LS) twins had a slightly higher rate of malformations than unlike-sex (US) twins (RR = 1.1), as well as a higher rate of CNS defects (RR = 3.0). The siblings also had a significantly increased rate of CNS defects compared to singletons (RR = 1.9), but not of cardiovascular defects (RR = 0.9). The results indicate that twins have elevated rates of at least some congenital malformations. The observations about CNS defects suggest common factors that can lead to either like-sex twinning, CNS defects, or both. The increased frequency of cardiovascular defects in twins appears to be associated with the biologic conditions of twinning.

Adult↗
PubMed1982

The association of twinning and neural tube defects: studies in Los Angeles, California, and Norway.

Accurate, unbiased malformation rates in twins must be obtained unselectively from population-based studies that include livebirths and stillbirths after a thorough ascertainment of cases. This type of study was conducted in Los Angeles County, California, where 28 twins with a neural tube defect (NTD) were identified. The prevalence in twins (1.6/1,000) was significantly higher than in singletons (1.1/1,000). The study then was expanded to include population-based data from the Medical Birth Registry of Norway which has a comparable overall NTD prevalence (1.0/1,000) and twinning rate (2%). The combined material shows a higher prevalence of anencephaly and encephalocele but not of spina bifida in twins compared to singletons. The male/female ratios in total twin and singleton cases were comparable (0.8), but varied by specific defect. Like-sex twin females appeared at highest risk for NTD as well as for fetal death. This study supports theories which associate NTDs with monozygotic twins, either through developmental disruptions that cause susceptibility to environmental agents or through a common etiology. Furthermore, it suggests that twins and singletons differ in their response to etiologic factors for the development of NTDs and that the development of each type of NTD may be related to different factors.

California↗
PubMed1982

Secular trends of neural tube defects by demographic subgroups in Norway, 1967-81.

The secular trends of NTDs by subgroups were investigated using data from the population-based Medical Birth Registry of Norway. During 1967-81, rates of total congenital malformations significantly increased by 4.1% annually. In contrast, there was an average annual decline of 1.6% in anencephaly rates and 0.4% in spina bifida rates. Annual rates of NTDs among twins decreased more (3.8%) than among singletons (1.6%). Females had an annual decline in rates (2.2%) that was greater than in males (0.7%). Separation of NTDs into two sub-groups based on the presence of multiple major malformations, revealed a significant decline of 2.1% annually in singles, whereas rates in multiples showed an increase of 3.3% annually. The different prevalence patterns revealed in various subgroups strongly suggest different etiologic entities. These should be further refined for elucidating etiologic factors. Furthermore, in prediction of current cases and evaluation of the effects of health services, the proportion of the various subgroups present should be considered.

Anencephaly↗
PubMed1982

Current trends in the incidence of neural tube defects.

To verify and investigate the reported decline of neural tube defects (NTDs) in the last decade, data from three different sources were examined: the Birth Defects Monitoring Program (BDMP), composed of newborn discharge diagnoses; the population-base Metropolitan Atlanta Congenital Defects Program (MACDP); and the National Center for Health Statistics (NCHS), whose data include only live births. Although the three systems use different methods of ascertaining cases, all data bases showed a decreasing trend in NTD rates, with annual percent decreases of 3.1% for NCHS, 5.7% for BDMP, and 7.7% for MACDP. The decrease was noted in all variables examined: race, sex, and birth status for each defect. NTD rates appear to be declining more rapidly in females than in males. Further, the rate among stillborn infants decreased more than the rate among live-born infants. The exclusion of stillbirths in the NCHS data may contribute to its low rate of decline for female anencephalics. Data from England showed a larger average annual decrease (10.6%) than did data from the United States. Although reasons for the overall decline are not verifiable, a variety of explanations are suggested for this decline and for the difference in NTD rate decline noted between live births and stillbirths. The overall decline in NTD rates should be investigated with respect to etiology; recognition of the decline is useful for planning and evaluating health care programs.

Anencephaly↗
PubMed1982

Neural tube defects among twin births.

To obtain accurate, unbiased rates of neural tube defects (NTDs) in twins, we conducted a population-based study that included live births and fetal deaths in Los Angeles County, California, ascertaining cases by multiple methods. Twenty-eight twin cases yielded a prevalence-at-birth of 1.6/1,000 twin births, which is significantly higher than the singleton prevalence of 1.1/1,000 births. In twins compared with singletons, the prevalences of both encephalocele and anencephaly are increased, whereas spina bifida is decreased. The twin case male/female sex ratio (.55) is lower than the singleton case sex ratio (.77). Concordance is relatively low at 3.7%, but appears to be higher than recently reported recurrence risks in other low prevalence areas. Stillbirths were most common among female cases and like-sex twins. Our study tends to support proposed etiologic theories associating NTDs with females or monozygotic twins, or both. There is increasing evidence that the etiology of NTDs may differ in high and low prevalence areas. We suggest also that twins and singletons may differ in their response to etiologic factors. The variations among anencephaly, spina bifida, and encephalocele in their association with twinning suggest that there may be different factors that influence the development of each specific NTD. The noted differences among the malformations also indicate that some of the variation among results of other studies of NTDs and twinning may be due to case ascertainment. Including spina bifida cases would decrease the proportion of twins in a study population, while including anencephalics would increase the proportion. Importantly, ascertaining fetal deaths would increase the proportion of anencephalics and case females, so studies of NTDs that do not include fetal deaths will show fewer twins than expected. On the basis of our findings and those of Layde et al., excluding encephaloceles will also decrease the number of twins among NTD cases. When investigating etiologic hypotheses for NTDs, these potential biases must be recognized.

Adult↗
PubMed1977

On the cysteine and cystine content of proteins. Differences between intracellular and extracellular proteins.

Analysis of published data on the cysteine and half-cystine content of proteins indicates that most intracellular proteins may be classified as sulfhydryl proteins (those containing cysteine but little or no half-cystine) and that such sulfhydryl proteins have a low cysteine content. The mean systeine content found for 32 intracellular mammalian proteins was 1.6% and intracellular proteins of many bacteria have similar or lower values. Extracellular mammalian proteins are primarily disulfide proteins (those containing half-cystine but little or no cysteine) have a high half-cystine content, the mean value found for some 34 extracellular mammalian proteins being 4.1%. This is contrasted with many of the extracellular proteins from facultative bacteria which are cyst(e)ine-free proteins, being lacking in both cysteine and half-cystine. These and related observations are interpreted in terms of the evolution of life in a reducing atmosphere and the subsequent transition to an oxidizing environment. It is suggested that disulfide proteins evolved primarily after the accumulation of oxygen in the atmosphere.

Bacterial Proteins↗
PubMedDate not supplied

Influence of exposure assessment methods on risk estimates in an epidemiologic study of total trihalomethane exposure and spontaneous abortion.

Trihalomethanes are common contaminants of chlorinated drinking water. Studies of their health effects have been hampered by exposure misclassification, due in part to limitations inherent in using utility sampling records. We used two exposure assessment methods, one based on utility-wide sampling averages, and one based on measurements from the utility sampling site closest to the subject's residence, to reestimate total trihalomethane (TTHM) exposure for 4212 participants in a preexisting study of risk factors for spontaneous abortion (SAB). For both approaches we performed unweighted, weighted, and subset analyses. The weighted and subset analyses were intended to reduce exposure misclassification, and were based on within-utility variance in TTHM measurements for the utility-wide average approach, and the distance between the subject's residence and sampling site for the closest-site approach. In general, the utility-wide average methods produced odds ratios equivalent to or slightly higher than the closest-site methods. Odds ratios obtained using the utility-wide average, but not the closest-site, approach also became progressively stronger in the weighted and subset analyses. A dose-response was seen between SAB and an exposure metric incorporating both TTHM concentration (utility-wide average approach) and personal ingestion, with SAB rates ranging from 8.3% to 13.7% (unweighted), 7.9% to 16.6% (variance weighted), and 6.6% to 23.1% (low-variance subset). Utility-wide average TTHM exposure assessment methods together with variance-based weights and subsets are relatively simple exposure assessment techniques, which may increase the epidemiologic usefulness of utility sampling records.

Abortion, Spontaneous↗
PubMedDate not supplied

Illness and absenteeism among California highway patrol officers responding to hazardous material spills.

Highway patrol officers are the primary responders to hazardous material spills in California, yet little is known regarding the health effects resulting from this exposure. A historical cohort study of 993 California highway patrol officers who responded to hazardous material spills in 1984 was conducted. The records of officers who were exposed to acutely toxic chemicals were followed for the subsequent week to determine if they demonstrated more absenteeism or illness compared to officers who were not exposed to toxic chemicals. No significant differences in the frequency of absenteeism or illness was found between the two groups during the week following exposure. No indication was found that exposure to hazardous materials during a highway patrol spill response results in increased absenteeism.

Absenteeism↗