A two-stage, genome-wide screen for susceptibility loci in primary Raynaud's phenomenon

ADRA2A and IRX1 are putative risk genes for Raynaud's phenomenon

Raynaud's phenomenon (RP) is a common vasospastic disorder that causes severe pain and ulcers, but despite its high reported heritability, no causal genes have been robustly identified. We conducted a genome-wide association study including 5,147 RP cases and 439,294 controls, based on diagnoses from electronic health records, and identified three unreported genomic regions associated with the risk of RP (p < 5 × 10-8). We prioritized ADRA2A (rs7090046, odds ratio (OR) per allele: 1.26; 95%-CI: 1.20-1.31; p < 9.6 × 10-27) and IRX1 (rs12653958, OR: 1.17; 95%-CI: 1.12-1.22, p < 4.8 × 10-13) as candidate causal genes through integration of gene expression in disease relevant tissues. We further identified a likely causal detrimental effect of low fasting glucose levels on RP risk (rG = -0.21; p-value = 2.3 × 10-3), and systematically highlighted drug repurposing opportunities, like the antidepressant mirtazapine. Our results provide the first robust evidence for a strong genetic contribution to RP and highlight a so far underrated role of α2A-adrenoreceptor signalling, encoded at ADRA2A, as a possible mechanism for hypersensitivity to catecholamine-induced vasospasms.

[Functional vascular acrosyndromes]

Vascular acrosyndromes are characterized by sparse, uniform clinical manifestations and a variety of possible pathomechanisms. The present article focuses on the functional entities. Raynaud phenomenon is based on cold- or stress-induced vasospasms of acral arteries. It is defined by the color changes of the skin, in the typical case white-blue-red (tricolore). The long fingers are most commonly affected. The etiology is unknown, and the pathophysiology is poorly understood. A distinction is made between primary and a secondary Raynaud phenomenon. The most important underlying diseases include collagenosis, primarily systemic sclerosis, and malignancies; furthermore, medications and drugs may promote vasospasm. Treatment is aimed at preventing or breaking the vasospasm, but has been only partially effective in doing so. Acrocyanosis is a vasospastic dystonic acral disorder that results in permanent reddish-livid discoloration, especially of the hands and feet. Secondary forms occur in collagenosis, malignancies, and myelodysplastic syndromes. The etiology and pathophysiology are virtually unknown. Targeted pharmacological intervention is not possible. Unlike all other vascular acrosyndromes, erythromelalgia is characterized by hyperemia. The primary form is a genetic sodium channelopathy, while secondary forms include malignancies, connective tissue diseases, and myelodysplastic syndromes. The symptoms are often distressing and disabling. Therapy requires a multimodal approach that includes both nonpharmacological and pharmacological strategies. Close interdisciplinary collaboration is essential for the management of this disease.

Raynaud's Phenomenon: Reviewing the Pathophysiology and Management Strategies

Raynaud's phenomenon (RP) is a multifactorial vasospastic disorder characterized by a transient, recurrent, and reversible constriction of peripheral blood vessels. RP is documented to affect up to 5% of the general population, but variation in its prevalence is commonly recognized owing to many factors, including varied definitions, gender, genetics, hormones, and region. Furthermore, RP may be idiopathic or be a clinical manifestation of an underlying illness. Patients with RP classically describe a triphasic discoloration of the affected area, beginning with pallor, followed by cyanosis, and finally ending with erythema. This change in color spares the thumb and is often associated with pain. Each attack may persist from several minutes to hours. Moreover, the transient cessation of blood flow in RP is postulated to be mediated by neural and vascular mechanisms. Both structural and functional alterations observed in the blood vessels contribute to the vascular abnormalities documented in RP. However, functional impairment serves as a primary contributor to the pathophysiology of primary Raynaud's. Substances like endothelin-1, angiotensin, and angiopoietin-2 play a significant role in the vessel-mediated pathophysiology of RP. The role of nitric oxide in the development of this phenomenon is still complex. Neural abnormalities resulting in RP are recognized as either being concerned with central mechanisms or peripheral mechanisms. CNS involvement in RP may be suggested by the fact that emotional distress and low temperature serve as major triggers for an attack, but recent observations have highlighted the importance of locally produced factors in this regard as well. Impaired vasodilation, increased vasoconstriction, and several intravascular abnormalities have been documented as potential contributors to the development of this disorder. RP has also been observed to occur as a side effect of various drugs. Recent advances in understanding the mechanism of RP have yielded better pharmacological therapies. However, general lifestyle modifications along with other nonpharmacological interventions remain first-line in the management of these patients. Calcium channel blockers, alpha-1 adrenoreceptor antagonists, angiotensin-converting enzyme inhibitors, nitric oxide, prostaglandin analogs, and phosphodiesterase inhibitors are some of the common classes of drugs that have been found to be therapeutically significant in the management of RP. Additionally, anxiety management, measures to avoid colder temperatures, and smoking cessation, along with other simple modifications, have proven to be effective non-drug strategies in patients experiencing milder symptoms.

Clinical features and risk factors of Raynaud's phenomenon in primary Sjögren's syndrome

Objective

The aim at the current study was to investigate the clinical characteristics and risk factors of Raynaud’s phenomenon (RP) in patients with primary Sjögren’s syndrome (pSS).

Methods

Retrospective analysis of the medical records of 333 new-onset pSS patients was performed. Demographic, clinical, and serological data were compared between individuals with and without RP. Logistic regression analysis was used to identify risk factors.

Results

RP was present in 11.41% of the pSS patients. pSS-RP patients were younger (49.74±14.56 years vs. 54.46±13.20 years, p=0.04) and exhibited higher disease activity (11 [5.75–15] vs. 7 [4–12], p=0.03) than those without. The prevalence of lung involvement was significantly higher in pSS patients with RP (60.53% vs. 17.29%; p<0.001). A significantly higher proportion of patients with pSS-RP tested positive about antinuclear (ANA), anti-RNP, and anti-centromere antibodies (ACA) compared to those without (p=0.003, <0.001, and 0.01, respectively). Multivariate analysis identified lung involvement (odds ratio [OR]=8.81, 95% confidence interval [CI] 2.02–38.47; p=0.04), anti-RNP positive status (OR=79.41, 95% CI 12.57–501.78; p<0.0001), as well as ACA (OR=13.17, 95% CI 2.60–66.72; p=0.002) as prognostic factors for pSS-RP.

Conclusion

The presence of RP defined a subset of pSS with a unique phenotype, manifesting as increased lung involvement and a higher frequency of anti-RNP antibodies and ACA, as well as greater disease activity. These results suggest that RP has clinical and prognostic value of pSS patients. Further prospective studies with a larger number of subjects are warranted to confirm our findings and assess the prognostic and treatment implications of RP in pSS patients.

Key Points • Raynaud’s phenomenon (RP) was present in 38 (11.41%) of 333 patients with primary Sjögren’s syndrome (pSS), with patients with RP exhibiting a younger age and higher disease activity. • The presence of RP indicates a subset of pSS with a unique phenotype, with manifestations including increased lung involvement and a higher frequency of anti-RNP antibodies and anti-centromere antibodies. • Patients with pSS and RP need close follow-up and long-term observation (including assessment of microangiopathy), with specific attention paid to the possible development of clinical features of systemic sclerosis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10067-021-05749-w.

Association of Raynaud's phenomenon with a polymorphism in the NOS1 gene

Background

Raynaud’s phenomenon (RP) describes the phenomenon of recurrent vasospasm of digital arteries, associated with skin colour changes: pallor, cyanosis and erythema. Twin studies have indicated a genetic predisposition for RP; however, the precise aetiology of RP remains unknown. It is thought that genetic variation in temperature-responsive or vasospastic genes might underlie RP so performed a candidate gene study in a large, population based sample. We assessed the association between RP and single nucleotide polymorphisms (SNPs) in the TRPA1, TRPM8, CALCA, CALCB and NOS1 genes.

Methods

Analysis included a total of 4276 individuals from the TwinsUK database. RP status had been determined using validated, self-administered questionnaires and was diagnosed in 640 individuals (17.6%). 66 tag SNPs across the candidate genes were tested for association with RP status using a linear regression model, accounting for covariates. Adjustment was made for multiple testing. RegulomeDB and GTEx databases were used to assess possible functional effects of the polymorphisms.

Results

Nominally significant associations between RP and four SNPs in NOS1 and one in CALCB were identified. After permutation testing, rs527590 SNP in NOS1 passed the significance threshold. RegulomeDB scores indicated an unlikely functional effect of this variant, while the survey of the GTEx database found the SNP and several variants in linkage disequilibrium to be cis-eQTLs in skin.

Conclusion

Results indicate that RP is associated with variation in gene NOS1. This finding may be related to the observation that the significant SNP in NOS1 is known to exhibit functional influence on the gene expression.

Raynaud's Phenomenon: A Brief Review of the Underlying Mechanisms

Raynaud’s phenomenon (RP) is characterized by exaggerated cold-induced vasoconstriction. This augmented vasoconstriction occurs by virtue of a reflex response to cooling via the sympathetic nervous system as well as by local activation of α_2C adrenoceptors (α_2C-AR). In a cold-initiated, mitochondrion-mediated mechanism involving reactive oxygen species and the Rho/ROCK pathway, cytoskeletal rearrangement in vascular smooth muscle cells orchestrates the translocation of α_2C-AR to the cell membrane, where this receptor readily interacts with its ligand. Different parameters are involved in this spatial and functional rescue of α_2C-AR. Of notable relevance is the female hormone, 17β-estradiol, or estrogen. This is consistent with the high prevalence of RP in premenopausal women compared to age-matched males. In addition to dissecting the role of these various players, the contribution of pollution as well as genetic background to the onset and prevalence of RP are also discussed. Different therapeutic approaches employed as treatment modalities for this disease are also highlighted and analyzed. The lack of an appropriate animal model for RP mandates that more efforts be undertaken in order to better understand and eventually treat this disease. Although several lines of treatment are utilized, it is important to note that precaution is often effective in reducing severity or frequency of RP attacks.

The 3p21.1-p21.3 Hereditary Vascular Retinopathy Locus Increases the Risk for Raynaud's Phenomenon and Migraine

Previously, we described a large Dutch family with hereditary vascular retinopathy (HVR), Raynaud's phenomenon and migraine. A locus for HVR was mapped on chromosome 3p21.1-p21.3, but the gene has not yet been identified. The fact that all three disorders share a vascular aetiology prompted us to study whether the HVR haplotype also contributed to Raynaud's phenomenon and migraine in this family. Whereas the parent-child transmission disequilibrium test (TDT) did not reach significance, the sibling TDT revealed that the HVR haplotype harbours a susceptibility factor for Raynaud's phenomenon and migraine. Identification of the HVR gene will improve the understanding of the pathophysiology of HVR, Raynaud's phenomenon and migraine.

Prevalence, risk factors and associations of primary Raynaud's phenomenon: systematic review and meta-analysis of observational studies

OBJECTIVE

To systematically review the literature with regard to the prevalence, incidence, risk factors and associations of primary Raynaud's phenomenon (PRP).

METHOD

A systematic review of the literature of observational studies for PRP was undertaken using five electronic databases. Any studies reporting prevalence, incidence and risk factors of PRP were collected. Relative risk or OR and 95% CI were extracted or calculated to present the association between risk factors and PRP. Random effects model was used to pool the results.

RESULTS

33 articles assessing a total of 33,733 participants were included in this analysis (2 cohort, 17 cross-sectional and 14 case-control studies). The pooled prevalence of PRP was 4.85% (95% CI 2.08% to 8.71%) in the general population. The pooled annual incidence of PRP was 0.25% (95% CI 0.19% to 0.32%). Risk factors and associations for PRP included female gender (OR=1.65, 95% CI 1.42 to 1.91), family history (OR=16.6, 95% CI 7.44 to 36.8), smoking (OR=1.27, 95% CI 1.06 to 1.53), manual occupation (OR=2.66 95% CI 1.73 to 4.08), migraine (OR=4.02, 95% CI 2.62 to 6.17), cardiovascular disease (OR=1.69, 95% CI 1.22 to 2.34) and marital status (married, OR=0.60, 95% CI 0.43 to 0.83). The definition of PRP varied considerably between studies.

CONCLUSIONS

This is the first systematic review of the prevalence, incidence, risk factors and associations of PRP. Further study using uniform strict criteria for the condition is required to confirm these findings, particularly the possible association with cardiovascular disease.

International consensus criteria for the diagnosis of Raynaud's phenomenon

Vasoconstriction accompanied by changes in skin color is a normal physiologic response to cold. The distinction between this normal physiology and Raynaud's phenomenon (RP) has yet to be well characterized. In anticipation of the 9th International Congress on Autoimmunity, a panel of 12 RP experts from 9 different institutes and four different countries were assembled for a Delphi exercise to establish new diagnostic criteria for RP. Relevant investigators with highly cited manuscripts in Raynaud's-related research were identified using the Web of Science and invited to participate. Surveys at each stage were administered to participants via the on-line SurveyMonkey software tool. The participants evaluated the level of appropriateness of statements using a scale of 1 (extremely inappropriate) through 9 (extremely appropriate). In the second stage, panel participants were asked to rank rewritten items from the first round that were scored as "uncertain" for the diagnosis of RP, items with significant disagreement (Disagreement Index > 1), and new items suggested by the panel. Results were analyzed using the Interpercentile Range Adjusted for Symmetry (IPRAS) method. A 3-Step Approach to diagnose RP was then developed using items the panelists "agreed" were "appropriate" diagnostic criteria. In the final stage, the panel was presented with the newly developed diagnostic criteria and asked to rate them against previous models. Following the first two iterations of the Delphi exercise, the panel of 12 experts agreed that 36 of the items were "appropriate", 12 items had "uncertain" appropriateness, and 13 items were "inappropriate" to use in the diagnostic criteria of RP. Using an expert committee, we developed a 3-Step Approach for the diagnosis of RP and 5 additional criteria for the diagnosis of primary RP. The committee came to an agreement that the proposed criteria were "appropriate and accurate" for use by physicians to diagnose patients with RP.

Synchronous Onset of Secondary Raynaud's Phenomenon in Monozygotic Twins

The heritability of primary Raynaud's phenomenon has been reported in previous works. In this paper we describe the simultaneous onset of Raynaud's phenomenon, rapidly evolved in acrocyanosis and diagnosed as secondary Raynaud's phenomenon, observed in monozygotic twins. This case supports the role of genetic factors in the pathogenesis of such disorder. Moreover, the singular synchronism of its appearance is discussed.

The pathogenesis, diagnosis and treatment of Raynaud phenomenon

The past 10 years have seen the publication of results from several multicentre clinical trials in primary and systemic sclerosis (SSc)-related Raynaud phenomenon. The publication of these studies has occurred as a result of new insights into the pathogenesis of Raynaud phenomenon, which are directing new treatment approaches, and increased international collaboration between clinicians and scientists. Although the pathogenesis of Raynaud phenomenon is complex, abnormalities of the blood vessel wall, of neural control mechanisms and of intravascular (circulating) factors are known to interact and contribute. Key players relevant in drug development include nitric oxide, endothelin-1, alpha adrenergic receptor activation, abnormal signal transduction in vascular smooth muscle, oxidative stress and platelet activation. The main advances in diagnosis have been a clearer understanding of autoantibodies and of abnormal nailfold capillary patterns as independent predictors of SSc, and widespread use and increased availability of capillaroscopy. The ultimate aim is to translate the advances made in the pathophysiology and early diagnosis into development of treatments to prevent and reverse digital vascular dysfunction and injury. This Review provides an update of the pathogenesis, diagnosis and treatment of Raynaud phenomenon. Current and future treatment approaches are discussed, and some key unanswered questions are highlighted.

The role of capillaroscopy in differentiation of primary and secondary Raynaud's phenomenon in rheumatic diseases: a review of the literature and two case reports

The purpose of this study is to study and systematize the current knowledge about the role of capillaroscopy in differentiation of primary and secondary Raynaud's phenomenon (RP) in rheumatic diseases. This method is a review of the literature. Capillaroscopy is of crucial value for diagnosis and differentiation of primary and secondary RP in rheumatic diseases. The appearance of abnormal capillaroscopic pattern inherits high positive predictive value for the development of systemic rheumatic disease. The most specific pattern is found in systemic sclerosis (SSc), so called "scleroderma pattern", which is characterized by the presence of dilated capillaries, hemorrhages, avascular areas and neoangiogeneis. It is found in more than 90% of patients with overt SSc. Similar changes are found in patients with dermatomyositis, mixed connective tissue disease, undifferentiated connective tissue disease and they are called "scleroderma-like pattern". Absence of abnormal capillaroscopic findings can be regarded as a diagnostic criterion for primary RP. Inclusion of pathologic capillaroscopic pattern may increase the sensitivity of ACR classification criteria for SSc. In conclusion, capillaroscopy is of crucial importance for the differentiation of primary and secondary RP in rheumatic diseases, and also in differentiation between different forms of connective tissue diseases as well as for their early diagnosis.

[Raynaud's phenomenon]

Raynaud's phenomenon is characterized by repeated daily attacks of ischemia followed by reperfusion at the acrallevel. It is a frequent syndrome found in medical practice; and it can be considered as primary or secondary to other conditions, including rheumatic autoimmune diseases. Current classification had clinical and therapeutic implications. Careful clinical evaluation is the most reliable and reproducible method in the diagnosis of Raynaud's phenomenon. Several risk factors had been associated in the genesis of Raynaud's phenomenon; however, its pathogenesis remains elusive although recently, considerable progress in disease mechanism had been described. Such advances are directing new lines of therapy.

Glutathione S-transferase M1 and GST T1 genetic polymorphisms and Raynaud’s phenomenon in French vinyl chloride monomer-exposed workers

Occupational vinyl chloride monomer (VCM) exposure can induce Raynaud's phenomenon (RP). However, not all VCM workers developed RP, which suggests an underlying genetic susceptibility. Genetic polymorphisms of glutathione S-transferases (GSTs), involved in VCM metabolism, have been shown to influence certain VCM-related health effects. We have conducted a case-control study of 58 subjects with RP along with 247 subjects without RP, from a population of 305 French workers exposed or formerly exposed to VCM, to assess any association between GST M1 and GST T1 gene polymorphisms, either separately or in combination, and the presence of RP. None of the GST M1 or GST T1 genotypes were significantly associated with the presence of RP among studied VCM workers. A combination of positive genotypes for both GST M1 and GST T1 was significantly associated with RP presence, compared to the other combinations of genotypes (OR=2.1, 95% CI=1.1-3.8). OR adjusted for age, smoking status, alcohol consumption and history of treated hypertension did not reach significance (OR=2.0, 95% CI=0.9-5.2). None of the GST M1 and GST T1 genotypes seem to contribute separately to the presence of RP, suggesting that they are not, when taken alone, a major determinant of interindividual variability for VCM-induced PR. However, the combination of both positive GST M1 and GST T1 genotypes appears to contribute slightly to susceptibility to RP in VCM-exposed subjects. Nevertheless, our study-the first to examine the role of a genetic component in the occurrence of RP secondary to occupational exposure to a chemical-corroborates the previous considerations that interaction between the genetic constitution and environmental factors is of importance in determining the health-adverse effects of VCM exposure.

Mechanisms of Raynaud's disease

Raynaud's phenomenon is due to transient cessation of blood flow to the digits of the hands or feet. An attack of Raynaud's phenomenon is classically manifested as triphasic color changes. The white phase is due to excessive vasoconstriction and cessation of regional blood flow. This phase is followed by a cyanotic phase, as the residual blood in the finger desaturates. The red phase is due to hyperemia as the attack subsides and blood flow is restored. An attack is frequently associated with pain and/or paresthesia due to sensory nerve ischemia. Variants of Raynaud's phenomenon include acrocyanosis and primary livedo reticularis, each of which is associated with reduced skin blood flow, exacerbated by cold or emotional upset. Raynaud's phenomenon in the absence of other disorders is primary Raynaud's phenomenon, or Raynaud's disease. The mechanisms of Raynaud's disease include increased activation of the sympathetic nerves, in response to cold or emotion; an impaired habituation of the cardiovascular response to stress may contribute. In addition, there appears to be a local fault, which is likely multifactorial. This local fault is due to an alteration in vascular function rather than vascular structure. The alteration in vascular function may be related to increased sensitivity to cold of the adrenergic receptors on the digital artery vascular smooth muscle. In some cases, locally released or systemically circulating vasoconstrictors may participate, including endothelin, 5-hydroxytryptamine and thromboxane. A deficiency or increased degradation of nitric oxide, possibly due to increased oxidative stress, may be involved in some cases. These recent pathophysiological insights may lead to new therapeutic options.

Aspects héréditaires et génétiques de la maladie de Raynaud

The pathophysiology of primary Raynaud's phenomenon (Raynaud's disease) remains uncertain but the transmission of this primary microcirculatory dysregulation seems strongly influenced by genetic factors. For a long time, physicians have found that the hereditary factor plays an important role in the genesis of Raynaud's disease. Familial analysis and twin studies have confirmed the role of an hereditary factor. It seems heterogeneous but pedigree analysis indicates the possibility of an autosomal dominant transmission influenced by sex, in some families, allowing an approach called "reverse genetic" based on linkage analysis. Such an approach has focused on few loci but sequencing of candidate genes for genetic mutations remains negative. Given the supposed heterogeneity of the genetic transmission of Raynaud's disease, diversification of strategies in molecular genetics is suitable with reference to techniques applied to multifactorial heredity.

Pathogenesis of Raynaud's phenomenon

The pathogenesis of Raynaud's phenomenon is not fully understood. However, the last 20 yr have witnessed enormous increases in our understanding of different mechanisms which, singly or in combination, may contribute. A key point is that Raynaud's phenomenon can be either primary (idiopathic) or secondary to a number of underlying conditions, and that the pathogenesis and pathophysiology vary between these conditions. This review concentrates upon those subtypes of Raynaud's phenomenon of most interest to rheumatologists: systemic sclerosis-related Raynaud's phenomenon, primary Raynaud's phenomenon and Raynaud's phenomenon secondary to hand-arm vibration syndrome. In this review, I shall discuss the main mechanisms thought to be important in pathophysiology under the three broad headings of 'vascular', 'neural' and 'intravascular'. While these are false distinctions because all interrelate, they facilitate discussion of the key elements: the blood vessel wall (particularly the endothelium), the neural control of vascular tone, and the many circulating factors which can impair blood flow and/or cause endothelial injury. Vascular abnormalities include those of both structure and function. Neural abnormalities include deficiency of the vasodilator calcitonin gene-related peptide (released from sensory afferents), alpha(2)-adrenoreceptor activation (possibly with up-regulation of the normally 'silent' alpha(2C)-adrenoreceptor) and a central nervous system component. Intravascular abnormalities include platelet activation, impaired fibrinolysis, increased viscosity and probably oxidant stress. As our understanding of the pathophysiology of Raynaud's phenomenon increases, so do our possibilities for identifying effective treatments.

A common genetic factor underlies hypertension and other cardiovascular disorders

Background

Certain conditions characterised by blood vessel occlusion or vascular spasm have been found to cluster together in epidemiological studies. However the biological causes for these associations remain controversial. This study used a classical twin design to examine whether these conditions are linked through shared environmental exposures or by a common underlying genetic propensity to vasospasm.

Methods

We investigated the association between hypertension, migraine, Raynaud's phenomenon and coronary artery disease in twins from a national register. Phenotype status was determined using a questionnaire and the genetic and environmental association between phenotypes was estimated through variance components analysis.

Results

Responses were obtained from 2,204 individuals comprising 525 monozygotic and 577 dizygotic pairs. There was a significant genetic contribution to all four traits with heritabilities ranging from 0.34 to 0.64. Multivariate model-fitting demonstrated that a single common genetic factor underlies the four conditions.

Conclusions

We have confirmed an association between hypertension, migraine, Raynaud's phenomenon and coronary artery disease, and shown that a single genetic factor underlies them. The demonstration of a shared genetic factor explains the association between them and adds weight to the theory of an inherited predisposition to vasospasm.

Treatment of Raynaud's phenomenon: new insights and developments

Although certain broad principles of treatment apply to all patients with Raynaud's phenomenon, the exact approach will vary depending on the nature and severity of the underlying digital vascular problem. Advances in the understanding of the pathophysiology of Raynaud's phenomenon are directing new lines of therapy. This review considers general (nonpharmacologic) measures, the different types of drug therapy, and the role of surgery. Recent advances in the use of more conventional treatments, such as calcium channel blockers, are discussed and also newer agents that are currently being researched, for example, endothelin-1 receptor antagonists and nitric oxide donors. The necessity of prompt assessment and treatment of acute digital ischemia, which is a medical emergency, is highlighted.

The genetics of systemic sclerosis

The etiopathogenesis of systemic sclerosis (SSc) is unclear. With no definitive evidence supporting an environmental cause, recent attention has focused on genetic factors. Familial clustering and ethnic influences have been demonstrated. Human leukocyte antigen (HLA) associations exist but are more related to the presence of particular autoantibodies rather than to the disease. In addition, no single major histocompatibility complex (MHC) allele predisposes to SSc in all ethnic groups. The role of microchimerism in SSc is a novel yet unproven hypothesis that may be related to intergenerational HLA compatibility. Recent studies investigating polymorphisms in genes coding for extracellular matrix proteins and cell-signaling molecules implicate non-MHC areas in SSc pathogenesis. The data reviewed suggest that SSc is a multigenic complex disorder.

Raynaud's phenomenon: epidemiology and risk factors

Although originally described more than 100 years ago, the pathophysiology of Raynaud's phenomenon (RP) remains incompletely understood. Epidemiologic studies have the potential to improve our understanding of the pathogenesis of RP and to identify potential targets for therapeutic interventions. Such studies require standardized instruments to accurately identify subjects with RP. Dr. Maricq was the first to develop and validate a standardized instrument to classify patients with this disorder. Her work has facilitated many of the epidemiologic studies of RP that are discussed in this review.

Genomewide scans of complex human diseases: true linkage is hard to find

Many "complex" human diseases, which involve multiple genetic and environmental determinants, have increased in incidence during the past 2 decades. During the same time period, considerable effort and expense have been expended in whole-genome screens aimed at detection of genetic loci contributing to the susceptibility to complex human diseases. However, the success of positional cloning attempts based on whole-genome screens has been limited, and many of the fundamental questions relating to the genetic epidemiology of complex human disease remain unanswered. Both to review the success of the positional cloning paradigm as applied to complex human disease and to investigate the characteristics of the whole-genome scans undertaken to date, we created a database of 101 studies of complex human disease, which were found by a systematic Medline search (current as of December 2000). We compared these studies, concerning 31 different human complex diseases, with regard to design, methods, and results. The "significance" categorizations proposed by Lander and Kruglyak were used as criteria for the "success" of a study. Most (66.3% [n=67]) of the studies did not show "significant" linkage when the criteria of Lander and Kruglyak (1995) were used, and the results of studies of the same disease were often inconsistent. Our analyses suggest that no single study design consistently produces more-significant results. Multivariate analysis suggests that the only factors independently associated with increased study success are (a) an increase in the number of individuals studied and (b) study of a sample drawn from only one ethnic group. Positional cloning based on whole-genome screens in complex human disease has proved more difficult than originally had been envisioned; detection of linkage and positional cloning of specific disease-susceptibility loci remains elusive.

Raynaud's phenomenon

Many persons are affected by the phenomenon known as Raynaud's. Raynaud's is classified in 2 ways-as Raynaud's disease or Raynaud's syndrome. Classification is based on the presence of associated conditions. Raynaud's is characterized by vasospasm-induced color changes of the fingers, toes, and ears. The fingers are most commonly affected. Studies involving cause, diagnosis, and treatment have been instituted with varied results. Diagnosis is primarily based on clinical symptoms involving digital color changes. Treatment is aimed at prevention of attacks and includes medication, stress reduction, and avoidance of vasoconstricting agents. Whether the phenomenon will develop into a more serious condition with which Raynaud's is associated is important. This article describes the etiology, pathophysiology, diagnosis, treatment, and nursing implications with regard to Raynaud's.

Raynaud's phenomenon

Raynaud's phenomenon is characterised by episodic vasospasm of the fingers and toes typically precipitated by exposure to cold. Mild Raynaud's is common and is not usually a harbinger of clinically important disability; its onset, however, can be startling and uncomfortable for patients, and the well recognised association in some cases with systemic rheumatic conditions often precipitates aggressive assessments for underlying diseases. Advances in vascular physiology have shed light on the role of the endothelium as well as endothelium-independent mechanisms in the altered vasoregulation of Raynaud's. We review clinical aspects of the disorder and new insights with respect to pathophysiology, and we discuss potential new therapeutics based on the disease mechanism, such as prostacyclin analogues, serotonin antagonists, and calcitonin gene-related peptides.