Biomedical subjects
K Christensen
Publications and source records attributed to K Christensen.
[Picture of the month. Schistosomiasis haematobia].
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Biodemographic trajectories of longevity.
Old-age survival has increased substantially since 1950. Death rates decelerate with age for insects, worms, and yeast, as well as humans. This evidence of extended postreproductive survival is puzzling. Three biodemographic insights--concerning the correlation of death rates across age, individual differences in survival chances, and induced alterations in age patterns of fertility and mortality--offer clues and suggest research on the failure of complicated systems, on new demographic equations for evolutionary theory, and on fertility-longevity interactions. Nongenetic changes account for increases in human life-spans to date. Explication of these causes and the genetic license for extended survival, as well as discovery of genes and other survival attributes affecting longevity, will lead to even longer lives.
Prenatal exposure to famine and health in later life.
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Low birth weight and preterm birth after short interpregnancy intervals.
OBJECTIVE: Our purpose was to study low birth weight and preterm birth after short interpregnancy intervals. STUDY DESIGN: Follow-up of a cohort of a register-based random sample of women who had at least two live births in Denmark between 1980 and 1992. Frequency of preterm birth (gestational age <37 weeks) and low birth weight (<2500 gm) were studied as a function of the interpregnancy interval in 10,187 women. RESULTS: Short interpregnancy intervals (< or =8 months) were associated with preterm birth but not with low birth weight. The adjusted odds ratios for preterm birth were 3.60 (95% confidence interval 2.04 to 6.35) for intervals up to 4.00 months and 2.28 (1.49 to 3.48) for intervals between 4.01 and 8.00 months compared with deliveries after 24 to 36 months, in which the risk of preterm birth was 3.5%. Risks were higher in women with a previous pregnancy at term. Social status, age, and parity were adjusted for. CONCLUSIONS: Short interpregnancy intervals were associated with an increased risk of premature delivery. This risk should be taken into account when planning a new pregnancy.
Estimating the critical molecular mobility temperature (T(K)) of amorphous pharmaceuticals.
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The genetic component of discrete disability traits: an analysis using liability models with age-dependent thresholds.
The presence of familial and genetic effects in the Activities-of-Daily-Life (ADL) data collected in the first wave of the 1995 Longitudinal Study of Aging of Danish Twins (LSADT) older than 75 is tested using multithreshold liability models of disability with age-dependent thresholds. These models are developed for discrete scores represented by five disability scales of male and female Danish twins. The presence of familial effects is revealed in all five scales of disability data for females and in three scales of data for males. Genetic effects are found to be significant in all four levels of aggregation of the Upper Limb-T (T = tiredness) disability scale for females and in the PADL-H (H = need for help) scale for males. Genetic effects are also pronounced in the Mobility-T scale for females and in the Lower Limb-T scale for males and females. For females, the genetic effects in the T-scale seem to be more pronounced than in the H-scale. For males, genetic effects are more pronounced in the H-scale. The estimates for MZ correlations in liability tend to be higher than the estimates for DZ correlations in almost all cases, which suggests that additional genetic effects may be revealed should the sample size of the ADL data be increased.
A population-based study of Graves' disease in Danish twins.
OBJECTIVE: The aetiology of Graves' disease (GD) is generally thought to fit a multi-factorial pattern of inheritance in which clinical disease develops on the basis of genetic susceptibility interacting with environmental and endogenous factors. In previous twin studies the probandwise concordance rates for hyperthyroidism were as high as 0.86 in monozygotic twins and 0.20 in dizygotic twins, indicating a very strong genetic influence. In these studies, however, no effort was made to distinguish between GD and non-autoimmune hyperthyroidism, and one study also included patients with simple non-toxic goitre, hampering if not invalidating any conclusions. The aim of the present study was to determine whether there is a genetic contribution in the aetiology of GD. DESIGN: Historical cohort study of pairs of same-sex twins, with information on GD being gathered by questionnaire surveys in the 1950s and 1960s. All available hospital material was sought to verify the diagnosis, which was assigned on the basis of clinical and histopathological evidence. The healthy co-twins were followed through middle age by questionnaire surveys in the 1970s and 1980s. PATIENTS: Same-sex twin individuals born between 1870-1920, included in a population-based nationwide register. A total of 118 subjects indicated hospitalization due to GD. A hospital record was available in 76 subjects. Of these, 55 (46 females and 9 males) could be classified as having GD. MEASUREMENTS: Pairwise and probandwise concordance rates for GD in monozygotic and dizygotic twin pairs. RESULTS: The probandwise concordance rates were 0.36 for monozygotic pairs and 0 for dizygotic pairs. The pairwise concordance rates were 0.22 and 0 for monozygotic and dizygotic pairs, respectively. The concordance rates were significantly (P = 0.012) higher in monozygotic than in dizygotic pairs. CONCLUSIONS: These results confirm that genetic factors play an important role in the aetiology of Graves' disease. However, they may not be as powerful as previously thought.
Risk of preterm delivery, low birthweight and growth retardation following spontaneous abortion: a registry-based study in Denmark.
BACKGROUND: Some studies have found an association between spontaneous abortion and adverse birth outcome in the subsequent pregnancy, but results are conflicting, maybe due to lack of confounder control. METHODS: Using population-based registries we identified a cohort of 45 449 women having a livebirth preceded by a spontaneous abortion ('abortion cohort'), and a random sample of 9752 women with two consecutive livebirths ('reference cohort'). We examined the risk of preterm (<37 weeks gestation) and very preterm delivery (<34 weeks), low birthweight and growth retardation in both births in the reference cohort compared with births following an abortion, controlling for social factors and interpregnancy interval. RESULTS: Compared to second births in the reference cohort, the abortion cohort had higher risks for preterm (odds ratio [OR] = 1.74, 95% CI: 1.5-2.0) and very preterm delivery (OR = 2.17, 95% CI : 1.7-2.7), low birthweight (OR = 1.76, 95% CI: 1.5-2.1), and growth retardation (OR = 1.50, 95% CI: 1.4-1.6). In the reference cohort 3.9% of the pregnancies ended as preterm deliveries, 1 % as very preterm, 3.3% as low birthweight, and 8.1% as growth retarded. Women with two or more previous abortions had a higher risk for preterm and very preterm delivery. When first liveborns of women in the reference cohort were compared with first liveborns in the abortion cohort, only deliveries before 34 and 37 weeks' gestation were associated with previous abortion. CONCLUSIONS: Spontaneous abortion is associated with preterm delivery (both <34 and <37 weeks) in the subsequent pregnancy. Women who become pregnant following an abortion should receive special attention in the antenatal clinics.
Mink 5S rRNA genes map to 2q in three loci suggesting conservation of synteny with human 1q.
By in situ hybridization we show that the SS rRNA genes in the mink map to chromosome 2q in three loci. The 2q1.1 locus containing 34% of the 5S rDNA, maps close to the centromere, and the remaining two loci of the 5S rDNA map to 2q1.3 (52%) and to 2q2.3. (14%). These data were obtained with a tritiated transcript of the 5S rRNA gene containing 121 bp. In a comparative FISH study performed with a biotinylated transcript of the 5S rRNA gene the procedure failed to detect the 2q2.3 site. A closely corresponding difference between the two procedures experienced previously in man and in the crab-eating macaque is discussed. The present results suggest a homology between 2q in the mink and part of 1q in man harbouring the 5S rRNA genes in 1q42.13 and 1q31, respectively.
Registration of congenital malformations in Denmark.
General registration of congenital malformations was established in Denmark in the early 1960s as a consequence of the thalidomide tragedy. The aims of the present paper are to describe the registration of congenital malformations in Denmark since the thalidomide tragedy, to discuss the limitations of these data and to point towards possibilities for improving the registration of congenital malformations in the future. Important components in a surveillance system are compulsory detailed reporting of malformations shortly after the diagnoses have been made and continuous expert evaluation of all reports. However, since 1995 the registration of congenital malformations in Denmark is based mainly on routine discharge diagnoses from hospitals. A high quality registration of congenital malformations in Denmark would be particularly valuable, because such a register together with existing health related registers and an ongoing large scale cohort study of pregnant women would provide a unique resource for etiological research in congenital malformations. Considering the consequences of congenital malformations for the affected children, their families and society, the establishment of a high quality registration of congenital malformations seems justifiable--and the Swedish experience shows that it is feasible.
Fecundability of female twins.
Animal studies have shown evidence of prenatal hormonal interaction between unlike sexed fetuses, including reduced fertility among females. We evaluated whether the fecundability of female twins is different from that of singletons and whether it differs according to the sex of the co-twin. The study was based on a questionnaire survey of 12,681 female twins born in the period 1953-1976 and an interview survey of 760 female controls born in the period 1953-1966, both in Denmark. Outcome of the first try ever to become pregnant (pregnant, still trying, stopped trying, pregnant despite contraception, and never tried) and the waiting time to pregnancy distribution did not differ among monozygotic, dizygotic same sexed, and dizygotic unlike sexed twins. More twins had a waiting time of less than 2 months, compared with singletons. This difference probably reflects an artifact due to the data collection method, because it disappeared when the cutoff point was changed to include 2 months for singletons, and we found no difference for longer waiting times. Hence, we found no increase in fecundability for twins compared with singletons, nor any reduced fecundability among female twins from unlike sexed pairs.
Intramedullary nailing of femoral fractures in adolescents.
A prospective study of adolescents with femoral fractures treated with intramedullary nailing was done to identify complications and evaluate the outcome of this method of treatment. Sixty patients with femoral fractures have been treated with antegrade intramedullary nailing. Magnetic resonance imaging scans were obtained to evaluate for subclinical avascular necrosis of the femoral head. The average patient age was 12 years. All patients had open physes at the time of surgery. Implants were removed in 33 patients to date at an average of 10 months after initial nailing. All but two patients continue to have no signs of avascular necrosis, no rotational or angular deformity, and no nerve palsy. Two patients have had subclinical avascular necrosis as seen on magnetic resonance imaging. One patient had avascular necrosis develop in both femoral heads 1 year after nail removal from the right femur. The second patient has asymptomatic marrow changes on magnetic resonance imaging consistent with avascular necrosis with no femoral head collapse. It is thought that intramedullary nailing of pediatric femoral fractures is a safe treatment option. Few complications and a small risk of subclinical presentation of avascular necrosis of the femoral head that can become evident after removal of the implant have been found.
Three polymorphic mink, Mustela vison, dinucleotide repeats.
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A polymorphic mink (Mustela vison) dinucleotide repeat.
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Spinal cord and nerve root blood flow in acute double level spinal stenosis.
STUDY DESIGN: Twenty-four pigs were randomized into three groups of eight pigs; a control group with 0% stenosis, a 25% stenosis group, and a 50% stenosis group. A fourth 75% stenosis group was added when results of the randomized experiment had been analyzed. Blood flow of the spinal cord and nerve roots and spinal evoked potentials were determined before and 1 hour after induction of the spinal stenoses. OBJECTIVES: To study the acute effects of different degrees of spinal stenosis on neural tissue blood flow and spinal evoked potentials. SUMMARY OF BACKGROUND DATA: Spinal cord dysfunction may be caused by vascular impairment or mechanical injury to neural tissue. Experimental double level compression of the cauda equina causes reversible nerve root edema, stasis, blood flow decrease, and compromised neural function. The vascular pathophysiology after spinal cord trauma was studied previously, and both increased and decreased neural tissue blood flow have been reported. METHODS: Two level spinal stenosis was introduced by placement of stenosing bands around the dural sac at L4 and L6. Neurologic function was monitored by sensory and motor evoked potentials. Regional blood flow (RBF) was measured in the stenotic segments between the bands and other regions of neural tissue by radioactive microspheres before and after induction of stenosis. RESULTS: Regional blood flow increased in the stenotic segments after 0% sham stenosis. Analysis of variance revealed no differences in RBF between the three randomized groups under comparable conditions of 0% stenosis. However, the RBF level of the added 75% group was lower than that of the other three groups. By comparison of RBF within groups before and after stenosis, no decrease in RBF was found between the stenosing bands in any of the groups. Fifty percent stenosis changed the amplitude of evoked potentials in half of the animals. Seventy-five percent stenosis caused severe changes in evoked potentials in 7 of 8 animals. CONCLUSIONS: Blood supply of the spinal cord and nerve roots in the segments between two central stenoses is preserved immediately after stenosis introduction by way of the segmental nerve pathway, even if nerve conduction is impaired.
Change in social status and risk of low birth weight in Denmark: population based cohort study.
OBJECTIVE: To estimate the risk of having a low birthweight infant associated with changes in social, environmental, and genetic factors. DESIGN: Population based, historical cohort study using the Danish medical birth registry and Statistic Denmark's fertility database. SUBJECTS: All women who had a low birthweight infant (< 2500 g) (index birth) and a subsequent liveborn infant (outcome birth) in Denmark between 1980 and 1992 (exposed cohort, n = 11,069) and a random sample of the population who gave birth to an infant weighing > or = 2500 g and to a subsequent liveborn infant (unexposed cohort, n = 10,211). MAIN OUTCOME MEASURES: Risk of having a low birthweight infant in the outcome birth as a function of changes in male partner, area of residence, type of job, and social status between the two births. RESULTS: Women in the exposed cohort showed a high risk (18.5%) of having a subsequent low birthweight infant while women in the unexposed cohort had a risk of 2.8%. After adjustment for initial social status, a decline in social status increased the absolute risk of having a low birthweight infant by about 5% in both cohorts, though this was significant only in the unexposed cohort. Change of male partner did not modify the risk of low birth weight in either cohort. CONCLUSION: Having had a low birthweight infant and a decline in social status are strong risk factors for having a low birthweight infant subsequently.
[Twin research--present and future potentials].
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