A revised estimate of twin concordance in systemic lupus erythematosus

Systemic lupus erythematosus: considerations for a genetic approach

There is a powerful evidence suggesting that etiology and pathogenesis of systemic lupus erythematosus has both genetic and environmental components. Unfortunately, understanding the genetics of lupus has been impeded by knowing the pattern of inheritance. Indeed, a complex mode of inheritance for the lupus disease phenotype is suggested by the known characteristics of this disorder. Twenty-five multiplex pedigrees for lupus have been enrolled and have been used to evaluate power to reveal linkage. The power to find linkage in these pedigrees is greater for autosomal recessive than for autosomal dominant modes of inheritance. Once 100 similar pedigrees are available for analysis our results predict that linkage is likely to be present for genetic models with relatively relaxed requirements. At loci operating by autosomal recessive inheritance linkage should be detectable despite genetic homogeneity as low as 40% and penetrance as low as 50%. For loci operating by autosomal dominant inheritance genetic homogeneity must be 60% or more when penetrance is as low as 50% to be able to establish linkage. Available preliminary data are also consistent with a possible genetic linkage of Fc gamma RIIIPMN with lupus in American Black pedigrees multiplex for lupus.

Future challenges in secondary prevention of breast cancer for women at high risk

We are making great progress in singling out those among us who are at high risk of cancer, whether on the basis of epidemiologic characteristics that predict risk in the absence of a firm knowledge of mechanism or, more recently, by specifying the genetic site of a factor that unequivocally puts a specific person in danger. We have been less capable of identifying factors that, given awareness of increased risk, determine whether or not a person adopts an appropriately self-protective behavior. This article reports the experience of female twins whose co-twins have a diagnosis of breast cancer. Such individuals can be assumed to have been presented with incontrovertible evidence of their elevated risk almost as much as if they had been found to have a dangerous gene. Their subsequent actions can shed light on why persons do not always take steps to protect themselves from a clear but future danger. It is evident that cognition is not the sole, or even the most important, determinant of health promoting behavior. Among the others are beliefs about cancer causality and the state of personal health, the details of the medical experience of relatives, and the degree to which perceptions of that experience have intruded into consciousness. The gap between rational and actual efforts to reduce personal risk is great, and if technology is to offer us the benefits promised, we must give priority to narrowing that gap.

Twin studies in rheumatic diseases

Twin studies attract both clinicians and geneticists because of the value of the twin method in helping unravel the genetic predisposition to diseases and the role of environment in their causation. In the field of rheumatology, there are many case reports on twins concordant or discordant for diseases. Interesting as such reports may be, very few generalizations can be made from them. The concordance rate among monozygotic (MZ) twins indicates the maximum level of genetic contribution. Based on studies of systematically compiled twin series, the concordance rate is about 15% for rheumatoid arthritis; the rate is probably of the same order of magnitude for systemic lupus erythematosus (SLE). The fine specificity of antinuclear antibodies of MZ twins at least one of whom is affected by SLE is very similar, despite somatic generation of immune diversity. Up to now, twin studies have provided little information on the role of environmental factors in rheumatic diseases. A notable exception is a case-control study of MZ twins discordant for smoking that reinforced the role of smoking as a cause of lumbar intervertebral disc degeneration.

Hypocomplementemic urticarial vasculitis syndrome in identical twins

Hypocomplementemic urticarial vasculitis syndrome (HUVS) is a syndrome of recurrent urticarial vasculitis, arthralgia/arthritis, and hypocomplementemia. Angioedema, ocular inflammation, glomerulonephritis, and obstructive lung disease are other clinical findings. Although the etiology of HUVS is unknown, its resemblance to systemic lupus erythematosus (SLE) suggests a similar pathogenesis. SLE is known to occur in identical twins. This is the first report of a pair of identical twins with HUVS. Concordance for HUVS in identical twins suggests that the pathogenesis of the disease involves abnormal genetic immunoregulation.

Anti-centromere antibodies (ACA) in systemic sclerosis patients and their relatives: a serological and HLA study

Autoantibody reactivity to centromere proteins CENP-A, CENP-B and CENP-C was examined in 58 patients with systemic sclerosis (SSc), 218 first degree relatives and 22 spouses. HLA class II typing for HLA-DRB1 and HLA-DQA1 was performed by restriction fragment length polymorphism (RFLP) analysis in 50 families, and HLA-DRB1, HLA-DQA1 and HLA-DQB1 typing was performed by olignucleotide typing in 44 families. Eleven probands and two relatives had ACA. The two relatives with ACA also had SSc. One relative was an identical twin sister of a proband with ACA and the other relative was a sister of a proband with ACA. All ACA-positive probands and relatives were female, and all recognized CENP-A, CENP-B and CENP-C. The presence of at least one HLA-DQB1 allele not coding for leucine at position 26 of the first domain appeared necessary, although not sufficient for the generation of ACA. Therefore within SSc families ACA is strongly associated with female gender and disease phenotype, and is at least in part genetically determined.

Twin studies in auto-immune disease

Immune-mediated diseases affect up to 5% of the population and are a major cause of morbidity and mortality. These diseases can be organ specific, such as insulin-dependent diabetes (IDDM) and non-organ specific, such as Rheumatoid Arthritis (RA). Identical and non-identical twins have been used to establish whether these diseases are determined by genetic or environmental factors. The results of these studies have been collated in a new section of the Mendel Institute in Rome. Diseases included in these studies included IDDM, RA, Systemic Lupus Erythematosus (SLE), Multiple Sclerosis (MS) and Myasthenia. Striking differences in concordance rates between identical and non-identical twins in all these studies suggest that genetic factors are important in causing these diseases. All the diseases are known to be associated with HLA genes on chromosome 6 which may account for some or all of the genetic susceptibility. However, in the majority of pairs the affected twin has an unaffected co-twin. These observations suggest that non-genetically determined factors, probably environmental factors and not somatic mutations, are critical. The study of unaffected co-twins, who are at high disease-risk, has allowed the identification of changes which precede and predict the clinical disease. The immune-mediated destruction in many of these diseases is probably caused by T-lymphocytes. Twin studies have shown the importance of genetic factors in determining T-cell responses. Identical twins should, therefore, provide the perfect test bed to assess the role of T-cells in immune-mediated diseases.

HLA-DP does not contribute towards susceptibility to systemic lupus erythematosus

OBJECTIVES

To determine whether HLA-DP genes are involved in determining susceptibility to systemic lupus erythematosus (SLE).

METHODS

HLA-DPA1 and DPB1 genes were amplified by PCR of DNA samples from a panel of patients with SLE and normal controls. Amplified DNA was blotted on to nylon filters and probed with sequence-specific oligonucleotide (SSO) probes.

RESULTS

No DPA1 or DPB1 allele was significantly associated with SLE, or with any immunological or clinical subset of SLE. Evidence was found for only limited linkage disequilibrium between HLA-DP and HLA-DQ/DR variants, and none between HLA-DP and the TAP2 gene.

CONCLUSIONS

These data indicate that HLA-DP genes do not contribute towards determining susceptibility to SLE.

Polymorphisms of the TAP2 transporter gene in systemic lupus erythematosus

OBJECTIVES

To determine whether the TAP2 transporter gene, which lies between HLA-DP and HLA-DQ, is involved in determining susceptibility to systemic lupus erythematosus (SLE).

METHODS

TAP2 types were determined by ARMS-PCR in 89 white patients with SLE and 156 control subjects.

RESULTS

No particular TAP2 dimorphism or allele was associated with SLE or with any clinical/immunological subgroup of SLE. Furthermore, there was no evidence for significant linkage disequilibrium between TAP2 and HLA-DQ/DR in SLE.

CONCLUSIONS

These data suggest that TAP2 is not a disease susceptibility gene for SLE and that the disease-predisposing haplotypes do not extend as far as TAP2. This indicates that any HLA-DP association with SLE must be independent of other class II (DQ/DR) associations.

Major histocompatibility complex genes and susceptibility to systemic lupus erythematosus in northern India

Fifty-eight patients with systemic lupus erythematosus (SLE) from Northern India were tissue typed for HLA class I and II antigens. The results revealed an appreciable increase of HLA-DR4 (37.5%) among patients compared with controls (17.9%), P < 0.03. Additionally, haplotype B8-DR3 was encountered frequently in the patient group. The findings suggest an important role of MHC genes in influencing susceptibility to SLE.

A strategy for assembling samples of adult twin pairs in the United States

In this paper we develop a methodology for the identification of large numbers of U.S. adult twin pairs. Data for this study derive from the U.S. Department of Defense and the Vietnam Era Twin (VET) Registry. The Department of Defense identified potential male twins (n = 10,002) using a computerized record linkage algorithm based on the same last name, same date of birth, and the same first five digits of the Social Security number. Twinship was confirmed by comparison with the Vietnam Era Twin Registry. We developed a logistic regression model that predicts the probability that a paired record identifies twins based on the absolute difference in the last four digits in the Social Security number, the age of issuance of the Social Security number, and the frequency of occurrence of the last name. We used the estimated coefficients derived from this regression model to assign predicted probabilities of being a twin to each matched record. There is a close correspondence between the observed and expected number of twins when evaluated across deciles of predicted probabilities of being a twin; the value of the Harrell's c index (c = 0.68 +/- 0.0004) indicates the overall predictive accuracy of the regression equation. The results from this study demonstrate the feasibility of identifying adult male-male twin pairs from any large computerized database that contains name, date of birth and Social Security number. However, the selection criteria used in the creation of the computer database must be clearly specified to avoid constructing a biased sample of twins.

Immune ablation with stem-cell rescue: a possible cure for systemic lupus erythematosus?

The impressive prolongation of survival has been the most important progress made in clinical systemic lupus erythematosus (SLE). Quality of life has also greatly improved, including pregnancy. However, persisting disease and therapy-related morbidity outcomes justify new approaches, different from the usual long-term palliative immunosuppression. Haematopoietic stem cells (HSCs) from healthy histocompatible mice are capable of curing murine SLE after eradication of the original HSCs with total body irradiation. Syngeneic and even autologous HSCs are also capable of curing induced experimental autoimmune diseases such as adjuvant arthritis and experimental allergic encephalomyelitis. In man allogeneic bone-marrow transplantation (BMT) is becoming progressively safer, but cannot yet be offered to SLE patients. However, syngeneic transplants from twins non-concordant for the disease would be justified. Conditioning with high-dose cyclophosphamide followed by autologous HSC rescue, from the marrow and/or from the peripheral blood, may already be regarded as a powerful immunosuppressive procedure for selected cases of SLE and other severe autoimmune diseases. Autologous transplant procedures are not saddled with the immunologic problems of allo-BMT. Although eradication of SLE may not be achieved by auto-BMT, minimal residual immunologic disease can be suppressed or controlled, and long-term self-maintained remissions may be expected.

Mammography and physician breast exams after the diagnosis of breast cancer in a twin or non-twin sister

Reports of breast-cancer-screening behavior were collected from 591 twin sisters of women with breast cancer and 182 non-twin sisters of the same women, and compared with the patterns found by national surveys. Timeline plots indicate that prior to the diagnosis of breast cancer in a sister, these women were being screened at prevailing rates. In the year after diagnosis, the annual frequency of use by them of both mammograms and physician breast exams increased by approximately 25 percent, but in subsequent years these rates dropped to a plateau no more than 10 to 15 percent higher than the baseline. The sisters over age 60 were screened with unusually low frequency, as were those with no partner in the home, those with no regular source of medical care, and especially the siblings of cases that died soon after the diagnosis. The relatively infrequent adoption of a long-term, annual, screening pattern in the face of certain knowledge of personal high risk gives cause for concern about the effectiveness of any intervention program requiring recognition of personal high risk for effectiveness. One cause for optimism is that higher screening rates prevail among those with co-twins diagnosed since 1980, suggesting that the increase in publicity and public education in recent decades has had a beneficial impact.

Genetic and immunological mechanisms in the pathogenesis of systemic lupus erythematosus

Recent research in systemic lupus erythematosus and animal models of lupus has provided new insight into the pathogenesis of this complex autoimmune disease. Progress has been made towards understanding the genetic contributions to disease susceptibility and induction, as well as towards elucidation of the lymphocyte abnormalities involved in pathogenic autoantibody production.