Factors affecting birthweight of rural Australian Aborigines

Aim : To examine factors affecting birthweight of Aboriginal infants in the Kimberley region of north-west Australia. Research design : A retrospective study of maternal and infant health records obtained through routine data collection. Subjects and methods : Birthweight and length of 2959 infants born to 1822 women from 1986 to 1994 were analysed. Mothers and infants were matched using unique identification codes. Index births and subsequent births to the same mother were collated in order to examine relative birth order effects and to calculate birth intervals. Results : Regression analysis showed significant associations between weight of the index birth and maternal age ( p < 0.001), remoteness of locality ( p < 0.01), sex of the infant ( p < 0.001) and maternal height ( p < 0.001). Length at birth was significantly associated with ethnicity of infant (Aboriginal vs Aboriginal/non-Aboriginal admixture, p < 0.05), sex ( p < 0.001), remoteness ( p < 0.01) and maternal height ( p < 0.001). Similar associations were observed for second and subsequent births. Birth interval was not associated with birthweight or length. Low birthweight was also more common to Aboriginal mothers compared with mothers of Aboriginal/non-Aboriginal admixture (13.1% vs 9.2%; &#104 2 = 5.1, p < 0.025) even though there were no differences in height between these two groups. Teenage mothers ( &#114 19 years) were no more likely to have low birthweight babies than older mothers. Of the variables examined, the only significant predictor of low birthweight was a previous low birthweight baby (relative risk = 4.45, p < 0.001). Conclusions : Short birth intervals and teenage births were not significant contributors to low birthweight in the present study. The high prevalence and duration of breastfeeding in the Kimberley may contribute to long average birth intervals. Pre-term birth, rather than intrauterine growth retardation, is likely to be the most common cause of low birthweight in this population.     

Factors affecting electromorph mutation rates in man: An analysis of data from Australian Aborigines

The constraints of molecular size and structure on the relative magnitudes of electromorph mutation rates as calculated indirectly have been studied using data for Australian Aborigines. The role of sample size in detecting rare electromorphs is important, In addition, subunit size shows a positive and subunit number a negative correlation with mutation rate. The differences in mutation rates were 2–9-fold when calculated for different categories of the data. The importance of physicochemical constraints are discussed.     

Immune dysfunction in Australian Aborigines

An examination of the prevalence and phenotype of immune disorders in different ethnic groups may provide important clues to the etiopathogenesis of these disorders. Whilst still conjectural the restricted and somewhat unique polymorphisms of the MHC (and other genetic loci involving host defences) of the Australian Aborigines may provide an explanation for their apparent heightened susceptibility to newly encountered infections and their resistance to many (auto) immune and allergic disorders. In comparison with non-Aboriginal Australians, Australian Aborigines have heightened frequencies of rheumatic fever, systemic lupus erythematosus, various infections and post-streptococcal glomerulonephritis. In contrast various autoimmune disorders (e.g. rheumatoid arthritis, multiple sclerosis, CREST, biliary cirrhosis, coeliac disease, pernicious anaemia, vitiligo), B27 related arthropathies, psoriasis, lymphoproliferative disorders and atopic disorders appear infrequent or absent. Similarly various autoantibodies occur with increased or diminished frequency. With continuing racial admixture, social deprivation and deleterious lifestyles of these people it is likely that further changes in both the frequencies and phenotype of these immune disorders will occur. It is only with a full understanding of the pathogenic mechanisms involved in these immune disorders that meaningful and clinical relevant interventions will be possible.     

Hepatitis B virus genotypes in Mongols and Australian Aborigines

Hepatitis B virus (HBV) is spread worldwide. Seven genotypes, A-G, have been described, differing by more than 8% of the genome. In eastern Asia and Oceania genotypes B and C are predominant. However, little is known about genotypes in Mongolia and Australian aborigines. We analysed the preS and S regions of HBV from 9 Mongols and 5 Australian Aborigines. All Mongolian strains were of genotype D and were most similar to Central Asian sequences. All the Australian strains were genetically of serotype ayw3, and could not be reliably classified by the S region analysis, but placed on a separate branch. By preS analysis, they were however clearly of genotype C. The 6-7% nucleotide difference from published Asian genotype C sequences suggests that they diverged from Asian genotype C branch more than 1000 years ago.     

Analysis of HLA class II allogenotyping in Australian Aborigines and Papua New Guinea populations

Human leukocyte antigen (HLA) class II allogenotyping has been applied to investigate the polymorphism of the DRB, DQB1, DQB2, DQA1, and DQA2 genes in Aborigines from the East Coast of Australia and in Melanesians from the Papua New Guinea North-East Coast and Highlands. Three new DR/DQ arrangements were observed, DRw14/DQB1-2b/DQA1-1a and DRw5Nauru/DQB1-3a/DQA1-2 (n Australian Aborigines), and DRw5Nauru/DQB1-1a/DQA1-1b (in Madang). DQA2 and DQB2 allogenotyping with TaqI and PstI digested genomic DNA revealed little polymorphism among the Papua New Guineans, with DQA2-Xa1 and DQB2-Xb1 the most common alleles in all the groups. However, the presence of DQA2-Xa2 in Papuans and Australian Aborigines reflects the degree of admixture with Caucasoids while the DQA2-Xa4 allele in Madang is probably a marker of Mongoloid origin.     

HLA class I variation in Australian Aborigines: characterization of allele B*1521

Abstract: Traditional methods of serological typing have largely used antisera of Caucasoid origin, which can overlook HLA heterogeneity in non-Caucasoid populations. Therefore, we have used molecular techniques to evaluate potential polymorphism in HLA class I molecules of Aborigines from the central desert and northern coast of Australia. The DNA sequence of common Aboriginal HLA-A and B antigens were compared with serological reaction patterns which suggested new polymorphisms. Although serological data indicated that long and short variants of A34 may exist, regardless of the serological pattern, all individuals carried the A*3401 allele. Therefore, the variation in A34 reaction pattern observed serologically was not attributable to primary sequence variation in the HLA A*3401 allele. Similarly, there was no detectable polymorphism in the sequences of selected HLA-B alleles, even though some of these alleles showed unusual serological reaction patterns. However, a new allele of B15 (B*1521) was detected in two individuals carrying this serotype. The cells from both of these individuals showed ambiguous reaction patterns with monospecific B62 and B75 sera. cDNA sequencing of the HLA B15 gene from these cells revealed a B15 allele that differed from B*1502 by a single nucleotide change. This change occurred at position 272, resulting in a C to G substitution at residue 67 in the consensus B15 cDNA sequence. Hence, the Australian Aborigines as an ethnic group show very little primary sequence polymorphism within the class I loci, consistent with the results obtained from previous serological studies.     

Factors affecting IgA related hyperviscosity

Sera from 14 patients with an IgA M-component, six of whom had myelomatosis and eight with benign monoclonal gammopathy (BMG) were analysed. All six sera from patients with high IgA (greater than 40 g/l) and total protein (greater than 100 g/l) concentrations were hyperviscous (HV). Four of these six patients also had hyperviscosity syndrome (HVS). There was no correlation between the quantity of IgA dimers or polymers and the presentation of HV and HVS. The binding between IgA and albumin and alpha 1-anti-trypsin was not covalent. Differences in the microenvironment of S-S bonds or of aromatic amino acids between isolated monoclonal monomeric and dimeric IgA were demonstrated with circular dichroism. Besides that, differences in hydrophobicity (exposure of aromatic amino acids) between IgA from normal serum and monomeric and dimeric IgA from a myeloma serum were revealed using hydrophobic interaction chromatography. The significance of hydrophobic interactions involving IgA and the influence of such forces on the circulation of the molecules are discussed.     

Factors affecting time to pregnancy

BACKGROUND: Both lifestyle factors and occupational and environmental factors have been suggested to affect the female reproductive system. In the present study, the separate and joint effects of several such factors are investigated. METHODS: Information on time to pregnancy (TTP) was available for 1578 women randomly selected from the general Swedish population. The information was collected retrospectively by using self-administered questionnaires. By means of logistic regression of survival data, fecundability odds ratios were determined for many factors. Multivariate models were used to determine which factors had the most impact on TTP. RESULTS: Several lifestyle factors were found to associate with TTP. However, only use of oral contraceptives prior to attempting to conceive, menstrual cycle length, age at conception and parity remained in the multivariate models. Together, these factors explained 14% of the variance in TTP. Excluding first and second month conceptions, only age at conception and menstrual cycle length remained in the multivariate models, together explaining only 8% of the variance in TTP. CONCLUSIONS: Although information on several factors was available, the multivariate model explained only a small fraction of the variation in the observed time to pregnancies. Furthermore, female biological factors seemed more important predictors of TTP than lifestyle factors.     

Factors affecting respiratory system stability

Periodic breathing (recurrent central apneas) occurs frequently during sleep. Periodic breathing can arise as a result of unstable behavior of the respiratory control system. A mathematical model of the respiratory control system was used to investigate, systematically, the effect of severity of disturbances to respiration and certain system parameters on periodic breathing occurring during sleep. The model consisted of multi-compartment representation of O₂ and CO₂ stores, a peripheral controller sensitive to O₂ and CO₂, and a central controller sensitive to CO₂. The effects of hypoxia and hypercapnia on the upper airway muscles were not considered in the model. Episodes of hyperventilation or asphyxia were used to disturb the control system and explore the boundaries of stable breathing. Circulation time and metabolic rate were also varied. Simulations with the model produced the following findings: The number of central apneas associated with periodic breathing were greater as circulation time increased; controller gain increases also made the number of apneas greater, although periodic breathing occurs with lower controller gains as circulation time increases. At each level of circulation time there was a range of controller gain changes which caused little change in the number of apneas. There were more apneas with hypoxia; also the number of apneas increased with sleep-associated reductions in metabolic rate. The more rapidly resting PCO₂ rose at sleep onset, the greater the likelihood of recurrent apneas. Finally, the more intense the disturbance, the more apneas there were.