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PubMed2024

Rare variant analyses in 51,256 type 2 diabetes cases and 370,487 controls reveal the pathogenicity spectrum of monogenic diabetes genes.

Type 2 diabetes (T2D) genome-wide association studies (GWASs) often overlook rare variants as a result of previous imputation panels' limitations and scarce whole-genome sequencing (WGS) data. We used TOPMed imputation and WGS to conduct the largest T2D GWAS meta-analysis involving 51,256 cases of T2D and 370,487 controls, targeting variants with a minor allele frequency as low as 5 × 10-5. We identified 12 new variants, including a rare African/African American-enriched enhancer variant near the LEP gene (rs147287548), associated with fourfold increased T2D risk. We also identified a rare missense variant in HNF4A (p.Arg114Trp), associated with eightfold increased T2D risk, previously reported in maturity-onset diabetes of the young with reduced penetrance, but observed here in a T2D GWAS. We further leveraged these data to analyze 1,634 ClinVar variants in 22 genes related to monogenic diabetes, identifying two additional rare variants in HNF1A and GCK associated with fivefold and eightfold increased T2D risk, respectively, the effects of which were modified by the individual's polygenic risk score. For 21% of the variants with conflicting interpretations or uncertain significance in ClinVar, we provided support of being benign based on their lack of association with T2D. Our work provides a framework for using rare variant GWASs to identify large-effect variants and assess variant pathogenicity in monogenic diabetes genes.

Diabetes Mellitus, Type 2↗

PubMed2005

Monogenic hypocholesterolaemic lipid disorders and apolipoprotein B metabolism.

The study of apolipoprotein (apo) B metabolism is central to our understanding of human lipoprotein metabolism. Moreover, the assembly and secretion of apoB-containing lipoproteins is a complex process. Increased plasma concentrations of apoB-containing lipoproteins are an important risk factor for the development of atherosclerotic coronary heart disease. In contrast, decreased levels of, but not the absence of, these apoB-containing lipoproteins is associated with resistance to atherosclerosis and potential long life. The study of inherited monogenic dyslipidaemias has been an effective means to elucidate key metabolic steps and biologically relevant mechanisms. Naturally occurring gene mutations in affected families have been useful in identifying important domains of apoB and microsomal triglyceride transfer protein (MTP) governing the metabolism of apoB-containing lipoproteins. Truncation-causing mutations in the APOB gene cause familial hypobetalipoproteinaemia, whereas mutations in MTP result in abetalipoproteinaemia; both rare conditions are characterised by marked hypocholesterolaemia. The purpose of this review is to examine the role of apoB in lipoprotein metabolism and to explore the key biochemical, clinical, metabolic and genetic features of the monogenic hypocholesterolaemic lipid disorders affecting apoB metabolism.

Abetalipoproteinemia↗

PubMed2006

Familial chilblain lupus, a monogenic form of cutaneous lupus erythematosus, maps to chromosome 3p.

Systemic lupus erythematosus is a prototypic autoimmune disease. Apart from rare monogenic deficiencies of complement factors, where lupuslike disease may occur in association with other autoimmune diseases or high susceptibility to bacterial infections, its etiology is multifactorial in nature. Cutaneous findings are a hallmark of the disease and manifest either alone or in association with internal-organ disease. We describe a novel genodermatosis characterized by painful bluish-red inflammatory papular or nodular lesions in acral locations such as fingers, toes, nose, cheeks, and ears. The lesions sometimes appear plaquelike and tend to ulcerate. Manifestation usually begins in early childhood and is precipitated by cold and wet exposure. Apart from arthralgias, there is no evidence for internal-organ disease or an increased susceptibility to infection. Histological findings include a deep inflammatory infiltrate with perivascular distribution and granular deposits of immunoglobulins and complement along the basement membrane. Some affected individuals show antinuclear antibodies or immune complex formation, whereas cryoglobulins or cold agglutinins are absent. Thus, the findings are consistent with chilblain lupus, a rare form of cutaneous lupus erythematosus. Investigation of a large German kindred with 18 affected members suggests a highly penetrant trait with autosomal dominant inheritance. By single-nucleotide-polymorphism-based genomewide linkage analysis, the locus was mapped to chromosome 3p. Haplotype analysis defined the locus to a 13.8-cM interval with a LOD score of 5.04. This is the first description of a monogenic form of cutaneous lupus erythematosus. Identification of the gene responsible for familial chilblain lupus may shed light on the pathogenesis of common forms of connective-tissue disease such as systemic lupus erythematosus.

Adolescent↗

PubMedDate not supplied

High "population attributable fraction" for coronary heart disease mortality among relatives in monogenic familial hypercholesterolemia.

PURPOSE: To estimate "population attributable fraction" (PAF) for coronary heart disease (CHD) mortality in a population of first-degree relatives of patients with monogenic familial hypercholesterolemia (FH) compared with the PAF for hypercholesterolemia in the general population. METHODS: PAF was calculated as [f(R - 1)/[1 + f(R - 1)]], where f is the frequency of the risk factor (hypercholesterolemia) and R is the relative risk for the association of hypercholesterolemia and CHD death. For FH relatives, f was assumed to be 50%, based on a fully penetrant, dominant mode of inheritance, and R values were obtained from the prospective Simon Broome Register data. PAFs for hypercholesterolemia and CHD death in the general population were based on the Framingham risk equations for the 95th percentile of cholesterol and CHD mortality. RESULTS: Over all ages, 44% and 57% of 5-year CHD mortality could potentially be prevented among male and female first-degree relatives in FH families, respectively, by cholesterol reduction. In contrast, values for 5-year CHD death for hypercholesterolemia in the general population were uniformly lower at all ages, with overall 5% and 10% of fatal CHD prevented among men and women, respectively. CONCLUSION: These results strongly support the view that family based testing strategies of relatives of probands with monogenic hypercholesterolemia, followed by effective lipid lowering drug treatment, is a highly effective way of reducing CHD deaths among these relatives.

Adult↗

PubMed1999

Basic mechanisms of monogenic inheritance.

To revive the appreciation of the importance of genetic studies for the understanding of neurologic diseases inherited in a monogenic fashion. After a description of the basic patterns of monogenic inheritance, the importance of linkage studies for the mapping of a disease gene is mentioned. Furthermore, the term linkage disequilibrium is introduced. Finally, several procedures used in current linkage analyses are briefly mentioned, with the aim of identifying the disease gene. The importance of genetic studies of disease families with many members, preferably from isolated surroundings to favor homogeneity, is stressed. However, such analyses can be performed only as a consequence of a close cooperation between clinicians and research scientists.

Animals↗

PubMed2001

Premature atherosclerosis associated with monogenic insulin resistance.

BACKGROUND: The common insulin resistance syndrome, with obesity, dyslipidemia, hyperglycemia, and hypertension, is associated with increased risk of atherosclerosis. Early atherosclerosis in rare monogenic forms of insulin resistance, however, has not been extensively documented. Cardiovascular end points were thus evaluated in subjects with Dunnigan-type familial partial lipodystrophy (FPLD) due to mutations at LMNA codon 482. METHODS AND RESULTS: FPLD subjects >/=35 years old were stratified by genotype for either the LMNA R482Q or R482W mutation. Twenty-three subjects were heterozygous mutation carriers, and 17 were R482/R482 homozygous family control subjects. All LMNA mutation carriers had FPLD with insulin resistance. In addition, LMNA mutation carriers had significantly more type 2 diabetes, hypertension, and dyslipidemia than normal family control subjects. Eight LMNA mutation carriers had coronary heart disease (CHD), compared with 1 normal control subject (OR 5.9, 95% CI 1.2 to 30.2). Six LMNA mutation carriers had CHD end points before age 55 years, and 4 of these, all women, had been hospitalized for CABG surgery between the ages of 35 and 54 years. CONCLUSIONS: Rare LMNA mutations that underlie FPLD with insulin resistance and hyperinsulinemia are also associated with early CHD, notably in women. This suggests that abnormalities of the nuclear envelope can result in a phenotype that recapitulates most of the important attributes of the common insulin resistance syndrome, including accelerated cardiovascular disease. FPLD thus appears to be an appropriate human monogenic model for the common insulin resistance syndrome.

Age Distribution↗

PubMed2005

Human ICOS deficiency abrogates the germinal center reaction and provides a monogenic model for common variable immunodeficiency.

The homozygous deletion of the inducible costimulator (ICOS), an activation-induced member of the CD28 family on T cells, causes an antibody deficiency syndrome in affected humans. The identification of a total of 9 ICOS-deficient patients revealed that this monogenic disease comprises the full clinical phenotype described for common variable immunodeficiency (CVID), including recurrent bacterial infections, adult as well as childhood onset, splenomegaly, autoimmune phenomena (autoimmune neutropenia), intestinal lymphoid hyperplasia, and malignancy (carcinoma of the vulva). All patients exhibited a profound hypogammaglobulinemia and a disturbed B-cell homeostasis. The severe reduction of class-switched memory B cells resulted from poor germinal center formation in the absence of ICOS. The additional decrease of naive B cells was associated with a partial inhibition of the early B-cell development at the pre-B-I stage. T-cell homeostasis seemed not to be affected, but low IL-10 production by ICOS-deficient T cells may contribute to the disturbed germinal center reaction. Human ICOS deficiency is indistinguishable from CVID and thus serves as a monogenic model for this complex syndrome.

Adult↗

PubMed2006

LINKAGE programs: linkage analysis for monogenic cardiovascular diseases.

Identification of the genes for a human disease provides significant insights into the molecular mechanism underlying the pathogenesis of the disease. A human disease gene can be identified by its chromosomal location (positional cloning). Linkage analysis is a key step in positional cloning. For monogenic disorders with a known inheritance pattern, model-based linkage analysis is effective in mapping the disease location. Therefore, model-based linkage analysis can provide a powerful tool to positional cloning of some specific molecular determinants that co-segregate with disease phenotypes in the isolated samples (e.g., large and multiplex impaired pedigrees). This chapter describes model-based human genetic linkage analysis as implemented in the LINKAGE computer package. First, we introduce the basic concepts and principles for genetic analysis of monogenic disorders. Then, we demonstrate the usages of the programs by analyzing several examples of hypothetical pedigrees with the inheritance modes of autosomal-dominant, autosomal-recessive, and genetic heterogeneity.

Cardiovascular Diseases↗

PubMed2006

Defining the genetic aetiology of monogenic diabetes can improve treatment.

A molecular genetic diagnosis is now possible for > 80% of patients with monogenic diabetes. This not only provides accurate information regarding inheritance and prognosis, but can inform treatment decisions and improve clinical outcome. Mild fasting hyperglycaemia caused by heterozygous GCK mutations rarely requires pharmacological intervention, whereas patients with mutations in the genes encoding the transcription factors HNF-1alpha and HNF-4alpha respond well to low doses of sulphonylureas. The recent discovery that mutations in the KCNJ11 gene (encoding the Kir6.2 subunit of the K(ATP) channel) are the most common cause of permanent neonatal diabetes, has enabled children to stop insulin injections and achieve improved glycaemic control with high doses of sulphonylurea tablets. Molecular genetic testing is an essential prerequisite for the pharmacogenetic treatment of monogenic diabetes.

Age of Onset↗

PubMed2007

Preimplantation genetic diagnosis for monogenic diseases: overview and emerging issues.

Preimplantation genetic diagnosis (PGD) is an established reproductive option for couples at risk of conceiving a pregnancy affected with a known genetic disease, who wish to avoid an (additional) affected child, termination of pregnancy or recurrent miscarriages. Early technologies concentrated on different approaches to direct mutation testing for monogenic diseases using single cell PCR protocols, or sex selection by fluorescent in situ hybridization for X-linked monogenic disease. Development of multiplex fluorescent PCR allowed simultaneously testing of linked markers alongside the mutation test, increasing the accuracy by controlling for contamination and identifying allele drop-out. The advent of highly effective whole genome amplification methods has opened the way for new technologies such as preimplantation genetic haplotyping and microarrays, thus increasing the number of genetic defects that can be detected in preimplantation embryos; the number of cases carried out and the new indications tested increases each year. Different countries have taken very different approaches to legislating and regulating PGD, giving rise to the phenomenon of reproductive tourism. PGD is now being performed for scenarios previously not undertaken using prenatal diagnosis, some of which raise significant ethical concerns. While PGD has benefited many couples aiming to have healthy children, ethical concerns remain over inappropriate use of this technology.

Biopsy↗

PubMed1996

Flow-cytometric investigation of epidermal cell characteristics in monogenic disorders of keratinization and their modulation by topical calcipotriol treatment.

A flow-cytometric study was performed in monogenic disorders of keratinization, to assess DNA distribution as well as the expression of keratins and involucrin. In addition, the changes in expression of these markers under influence of calcipotriol treatment were investigated. Proliferation, measured by the percentage of epidermal cells in SG2M-phase of the cell cycle, was increased in Darier's disease, lamellar ichthyosis, congenital bullous ichthyotic erythroderma of Brocq and the Comel-Netherton syndrome, whereas normal proliferation was found in autosomal dominant ichthyosis vulgaris, X-linked recessive ichthyosis, keratosis pilaris, ichthyosis bullosa of Siemens and the Sjögren-Larsson syndrome. Keratin 6 was enhanced in erythrodermic lamellar ichthyosis, congenital bullous ichthyotic erythroderma of Brocq and the Comel-Netherton syndrome, showing also reduction of keratin 10. Involucrin was only slightly reduced in erythrodermic lamellar ichthyosis, congenital bullous ichthyotic erythroderma of Brocq and the Comel-Netherton syndrome, compared to the pronounced reduction in all other skin disorders studied. Calcipotriol was found to enhance differentiation in Darier's disease, erythrodermic lamellar ichthyosis, and congenital bullous ichthyotic erythroderma of Brocq. Only Darier's disease did not show clinical improvement. In conclusion, flow cytometry provides a useful method for quantification of epidermal cell characteristics in monogenic disorders of keratinization. Further studies need to be performed to establish its usefulness as a diagnostic and prognostic tool.

Administration, Topical↗

PubMed1999

Monogenic disorders of obesity and body fat distribution.

Recently, great progress has been made towards understanding the molecular basis of body fat regulation. Identification of mutations in several genes in spontaneous monogenic animal models of obesity and development of transgenic models have indicated the physiological roles of many genes in the regulation of body fat distribution. In humans, mutations in leptin, leptin receptor, prohormone convertase 1 (PC1), pro-opiomelanocortin (POMC), melanocortin 4-receptor (MC4-R), and peroxisome proliferator-activated receptor (PPAR) gamma2 genes have been described in patients with severe obesity. Most of these obesity disorders exhibit a distinct phenotype with varying degrees of hypothalamic and pituitary dysfunction and a recessive inheritance, whereas MC4-R mutation has a nonsyndromic phenotype with dominant inheritance. These mutations suggest the critical role of central signaling systems composed of leptin/leptin receptor and alpha-melanocyte stimulating hormone/MC4-R in human energy homeostasis. Although the genetic basis of monogenic disorders of body fat distribution, such as congenital generalized lipodystrophy and familial partial lipodystrophy, Dunnigan variety, is still unknown, the genes for these have recently been localized to chromosomes 9q34 and 1q21-22, respectively. The advances in our knowledge of the phenotypic manifestations and underlying molecular mechanisms of genetic body fat disorders may lead to better treatment and prevention of obesity and other disorders of adipose tissue in the future.

Adipose Tissue↗

PubMed1999

Pachygyria/hypogenitalism: A monogenic syndrome.

We describe the clinical and neuroimaging findings of two severely retarded boys born to consanguineous parents. This appears to be a monogenic condition of abnormal neuronal migration associated with hypogenitalism. Reports of other monogenic syndromes of neuronal migration abnormalities are reviewed.

Cell Movement↗

PubMed2002

Identification of a monogenic locus (jams1) causing juvenile audiogenic seizures in mice.

Epilepsy is a debilitating disease with a strong genetic component. Positional cloning has identified a few genes for rare monogenic epilepsy syndromes; however, the genetics of common human epilepsies are too complex to be analyzed easily by current techniques. Mouse models of epilepsy can further this analysis by eliminating genetic background heterogeneity and enabling the production of sufficient numbers of offspring. Here, we report that Black Swiss mice have a heretofore unrecognized specific susceptibility to audiogenic seizures. These seizures are characterized by wild running, loss of righting reflex, and tonic flexion and extension, and are followed by a postictal period. The susceptibility to these seizures is developmentally regulated, peaking at 21 d of age and nearly disappearing by adulthood. Interestingly, both the susceptibility to seizures and their developmental regulation appear unrelated to hearing thresholds in the Black Swiss strain and backcrossed progeny. Genetic mapping and linkage analysis of hybrid mice localize the seizure gene, jams1 (juvenile audiogenic monogenic seizures), to a 1.6 +/- 0.5 centimorgan (cM) region on mouse chromosome 10, delimited by the gene basigin (Bsg) and marker D10Mit140. Interestingly, the majority of the critical region is syntenic to a region on human chromosome 19p13.3 implicated in a familial form of juvenile febrile convulsions. Cloning the gene for audiogenic seizures in these mice may provide important insight into the fundamental mechanisms for developmentally regulated human epilepsy syndromes.

Acoustic Stimulation↗

PubMed2003

[Monogenic hereditary diseases].

Monogenic disorders are caused by the inheritance of single gene mutations; alternatively, a monogenic disorder arises as a consequence of a de novo mutation in either the paternal or maternal germ line. The exponential increase in our understanding of the human genome has resulted in the localisation and cloning of a vast number of disease genes which has enabled the precise characterization of the underlying molecular defect in many of these disorders. Single nucleotide substitutions and microdeletions are the major types of disease-related mutations, but more complex mutations have also been described.

Genes, Dominant↗

PubMedDate not supplied

[Genetics and arterial hypertension: monogenic forms].

Hypertension is a complex, multifactorial disease; genetic factors represent one third to half of the inter-individual variability of blood pressure values. The study of genes involved in rare forms of monogenic hypertension led to the identification of pivotal pathophysiological pathways of kidney sodium and water reabsorption that can influence blood pressure values when changed. Glucocorticoid-Remediable Aldosteronism (GRA) is characterised by normal to high aldosterone levels, despite plasma renin activity suppression, and by the fact that these alterations are corrected by exogenous glucocorticoid administration. Apparent Mineralocorticoid Excess (AME) is due to a mutation of the gene encoding the renal isoform of 11 â HSD enzyme; the non-conversion of cortisol to cortisone result in increasing cortisol levels that activate the mineralocorticoid receptor. Early onset hypertension exacerbating during pregnancy is caused by a mutation leading to a conformational change in the mineralocorticoid receptor. Therefore, substances that are normally inactive at this level, such as progesterone, become potent agonists of the mutated receptor. Liddle's syndrome (or type I pseudo-hyperaldosteronism (PHA1), is characterised by a constitutive activation of the epithelial sodium channels in the distal tubule, causing an increase in sodium and chloride reabsorption. Gordon syndrome (Type II pseudo-hyperaldosteronism, PHA2) differs from the other forms because of the presence, in addition to hypertension, of hyperkaliemia and hyperchloremic acidosis that can be normalized with thiazide diuretics. Finally, a large pedigree of Turkish origin has been described: these patients are affected by an uncertain form of monogenic hypertension associated with brachydactyly.

Glucocorticoids↗

PubMed2006

[Monogenic forms of diabetes mellitus].

Through the years the evolution of the concepts in the different classifications of Diabetes Mellitus keep a close relationship with the advance of the scientific knowledge of this matter. In this way the last classification adopted in 1995 by the American Association of Diabetes and the World Health Organization has an etiologic basis, but in some aspects is already obsolete. With the new knowledges this classification should be modified including a group dedicated to monogenic diabetes. In this group should be considered diabetes MODY 1 to 6, constituted by the forms expressed by mutations of transcription factors and the glucokinase enzyme. There are other patients named MODY X, because the responsible genes of the diseases have not been identified yet. Also in this section might be included the mutations of the Kir6.2 subunit of the K+ channel recently described in the beta cell. It is possible that in a near future other forms will be described, which will contribute to a better understanding of the monogenic diabetes.

Adult↗

PubMed1998

[Parkinson disease: monogenic forms and genetic susceptibility factors].

Parkinson's disease (PD) is one of the most frequent neurodegenerative disorders. The role of genetic factors in its pathogenesis is supported by several lines of evidence: the high concordance in twins using PET scan; the increased risk among relatives of PD patients in case control and family studies; the existence of monogenic forms of PD. the alpha-synuclein gene is involved in a rare dominant form of the disease for which a new locus has been recently mapped to chromosome 2. Early onset autosomal recessive parkinsonism, which maps to chromosome 6q, appears to be frequent in Japan and in Europe. The genes for several monogenic forms of this entity should be identified soon, providing new insight into the pathophysiology of the disease. However, it is not clear if these genes will be relevant to apparently sporadic cases. In the long term, genotyping of affected sib-pairs should permit localisation and identification of other genetic susceptibility factors. These complementary approaches will contribute to the elucidation of the mechanism of PD and should provide new targets for drug therapies.

Chromosomes, Human, Pair 2↗