Catherine Massart

Mandibuloacral Dysplasia Is Caused by a Mutation in LMNA-Encoding Lamin A/C

Mandibuloacral dysplasia (MAD) is a rare autosomal recessive disorder, characterized by postnatal growth retardation, craniofacial anomalies, skeletal malformations, and mottled cutaneous pigmentation. The LMNA gene encoding two nuclear envelope proteins (lamins A and C [lamin A/C]) maps to chromosome 1q21 and has been associated with five distinct pathologies, including Dunnigan-type familial partial lipodystrophy, a condition that is characterized by subcutaneous fat loss and is invariably associated with insulin resistance and diabetes. Since patients with MAD frequently have partial lipodystrophy and insulin resistance, we hypothesized that the disease may be caused by mutations in the LMNA gene. We analyzed five consanguineous Italian families and demonstrated linkage of MAD to chromosome 1q21, by use of homozygosity mapping. We then sequenced the LMNA gene and identified a homozygous missense mutation (R527H) that was shared by all affected patients. Patient skin fibroblasts showed nuclei that presented abnormal lamin A/C distribution and a dysmorphic envelope, thus demonstrating the pathogenic effect of the R527H LMNA mutation.

Variation in Serum and Plasma PTH Levels in Second-Generation Assays in Hemodialysis Patients: A Cross-sectional Study

BACKGROUND Previous reports show that parathyroid hormone (PTH) concentrations may vary widely depending on the assay used to assess PTH. In this cross-sectional study, we aim to determine the usefulness of standardizing blood handling for optimal interpretation of PTH in patients with chronic kidney disease. STUDY DESIGN Diagnostic test study. SETTING & PARTICIPANTS Predialysis blood was sampled in 34 long-term hemodialysis patients at a single academic medical center. INDEX TEST PTH was measured by using 6 different automated second-generation assays (Elecsys, Advia Centaur, LIAISON, Immulite, Architect, and Access assays), 3 blood specimen types (serum, EDTA plasma, and citrate plasma), and 2 consecutive days of measurement (after thawing and 18 hours later with samples having been let at room temperature). REFERENCE TEST None. RESULTS A mixed statistical analysis model showed that the nature of the assay (P < 0.001) and nature of the blood sample (P < 0.001) significantly influenced variability in PTH concentrations, whereas day of measurement (day 1 or 2) did not (P = 0.5). Most PTH variability was caused by observations (96.8%), then manufacturers kit (2.5%), and last, specimen type (0.7%). PTH concentrations measured in citrate plasma were lower with every assay method used than those observed in serum or EDTA plasma. The interaction between manufacturer and specimen type was of moderate statistical significance (P = 0.04). To evaluate the potential clinical consequence of PTH measure variability, we classified patients according to Kidney Disease Outcomes Quality Initiative cutoff values (PTH < 150 pg/mL; PTH, 150 to 300 pg/mL; and PTH > 300 pg/mL). Overall, statistical classification agreement was moderate to high for comparison between assays and high to very high between different blood samples and between days of measurement. However, we found that up to 11 of 34 patients were classified in different categories with some assays (LIAISON versus Architect) and up to 7 of 34 in different categories with different blood specimen type (citrate plasma versus serum [corrected] in LIAISON assay). LIMITATIONS This is a cross-sectional study that used single lots of reagents. There currently is no reference method for the measurement of PTH and no recombinant PTH standard for PTH assay. CONCLUSION PTH variability caused by the nature of the assay and/or blood specimen type is large enough to potentially influence clinical decision making. A specified collection method therefore should be used for PTH measurements. In routine practice, we recommend serum PTH over EDTA or citrate plasma.

Multitissular involvement in a family with LMNA and EMD mutations Role of digenic mechanism

Background: Mutations in the EMD and LMNA genes, encoding emerin and lamins A and C, are responsible for the X-linked and autosomal dominant and recessive forms of Emery–Dreifuss muscular dystrophy (EDMD). LMNA mutations can also lead to several other disorders, collectively termed laminopathies, involving heart, fat, nerve, bone, and skin tissues, and some premature ageing syndromes. Methods: Fourteen members of a single family underwent neurologic, electromyographic, and cardiologic assessment. Gene mutation and protein expression analyses were performed for lamins A/C and emerin. Results: Clinical investigations showed various phenotypes, including isolated cardiac disease (seven patients), axonal neuropathy (one patient), and a combination of EDMD with axonal neuropathy (two patients), whereas five subjects remained asymptomatic. Genetic analyses identified the coincidence of a previously described homozygous LMNA mutation (c.892C→T, p. R298C) and a new in-frame EMD deletion (c.110-112delAGA, p. delK37), which segregate independently. Analyses of the contribution of these mutations showed 1) the EMD codon deletion acts in X-linked dominant fashion and was sufficient to induce the cardiac disease, 2) the combination of both the hemizygous EMD and the homozygous LMNA mutations was necessary to induce the EDMD phenotype, 3) emerin was present in reduced amount in EMD-mutated cells, and 4) lamin A/C and emerin expression was most dramatically affected in the doubly mutated fibroblasts. Conclusions: This highlights the crucial role of lamin A/C–emerin interactions, with evidence for synergistic effects of these mutations that lead to Emery–Dreifuss muscular dystrophy as the worsened result of digenic mechanism in this family.

Associations between visceral adipose tissue, inflammation and sex steroid concentrations in men

In men, obesity and the metabolic syndrome are accompanied by decreased testosterone levels, but little is known about the associations between visceral adipose tissue (VAT), VAT‐related inflammation and sex steroids.

Intermethod Variability in TSH-Receptor Antibody Measurement: Implication for the Diagnosis of Graves Disease and for the Follow-Up of Graves Ophthalmopathy

BACKGROUND We compared the analytical and clinical performance of 3 porcine thyroid receptor antibody (TRAb) methods (1 second- and 2 new third-generation systems) with the conventional TRAb assay based on the human recombinant TSH receptor (hTRAK). PATIENTS AND METHODS We obtained sera from 86 patients with untreated Graves disease (GD) and 71 healthy controls. We measured TRAb concentrations by radioreceptor assay using the hTRAK (Brahms) or the porcine TSH receptor (pRRA) from Beckman-Coulter, by electrochemiluminescence immunoassay (ECLIA) with the Elecsys/Cobas (Roche), and by ELISA using the Medizym TRAb clone (Medipan). RESULTS Between-run assay imprecision was < or =10% and < or =7.6% for hTRAK and ECLIA, but reached 14% and 14.9% for ELISA and pRRA, respectively. Maximal specificity and sensitivity close to 100% were obtained for hTRAK, ECLIA, and ELISA. pRRA failed to detect positive TRAbs in 5 GD patients. Although calibrated against the same reference standard 90/672, the assays displayed a high intermethod variability. The results were significantly higher by ECLIA and lower by ELISA and pRRA compared with hTRAK. Patients with ophthalmopathy had higher TRAb results by ELISA and pRRA than those without eye disease. CONCLUSIONS Second- and third-generation TRAb assays had similar diagnostic sensitivities in the diagnostic evaluation of GD. Despite the use of the same reference standard for calibration, high intermethod variability in TRAb assay results was seen in untreated GD patients. Assay harmonization is necessary for correct interpretation in the follow-up of Graves ophthalmopathy.

Vitamin D deficiency, vitamin D receptor gene polymorphisms and cardiovascular risk factors in Caribbean patients with type 2 diabetes

AIM The prevalence of diabetes in the French West Indies is three times higher than in mainland France. We aimed to assess the associations between vitamin D deficiency, vitamin D receptor (VDR) gene polymorphisms and cardiovascular risk factors in Caribbean patients with type 2 diabetes (T2D). METHODS In this cross-sectional study of 277 patients, 25-hydroxyvitamin D was measured by radioimmunoassay. FokI, BsmI, ApaI and TaqI single nucleotide polymorphisms (SNPs) of the VDR gene were genotyped. Analysis of covariance and logistic regression were performed. RESULTS The study included 76 patients of Indian descent and 201 patients of African descent. The prevalence of vitamin D deficiency (<20 ng/mL) was 42.6%. When patients were classified into groups with (G1) and without (G2) vitamin D deficiency, there were no significant differences in age, systolic blood pressure, low-density lipoprotein cholesterol and HbA(1c), although body mass index was significantly higher in G1. Vitamin D deficiency was significantly associated with increased diastolic blood pressure and triglyceride levels, and reduced high-density lipoprotein cholesterol (P<0.05). Prevalence of vitamin D deficiency was decreased in patients carrying the f allele of FokI (OR: 0.52; P=0.02) and the aa genotype of ApaI (OR: 0.46; P=0.05). BsmI and TaqI SNPs were not associated with vitamin D deficiency. CONCLUSION The rate of vitamin D deficiency was high in our T2D patients, and was associated with the VDR gene FokI and ApaI polymorphisms and cardiovascular risk profile. Measurements of vitamin D may help to detect T2D patients with cardiovascular risk, and VDR polymorphisms might explain why vitamin D deficiency is so frequently seen in some T2D patients.

Type B mandibuloacral dysplasia with congenital myopathy due to homozygous ZMPSTE24 missense mutation

Mutation in ZMPSTE24 gene, encoding a major metalloprotease, leads to defective prelamin A processing and causes type B mandibuloacral dysplasia, as well as the lethal neonatal restrictive dermopathy syndrome. Phenotype severity is correlated with the residual enzyme activity of ZMPSTE24 and accumulation of prelamin A. We had previously demonstrated that a complete loss of function in ZMPSTE24 was lethal in the neonatal period, whereas compound heterozygous mutations including one PTC and one missense mutation were associated with type B mandibuloacral dysplasia. In this study, we report a 30-year longitudinal clinical survey of a patient harboring a novel severe and complex phenotype, combining an early-onset progeroid syndrome and a congenital myopathy with fiber-type disproportion. A unique homozygous missense ZMPSTE24 mutation (c.281T>C, p.Leu94Pro) was identified and predicted to produce two possible ZMPSTE24 conformations, leading to a partial loss of function. Western blot analysis revealed a major reduction of ZMPSTE24, together with the presence of unprocessed prelamin A and decreased levels of lamin A, in the patients primary skin fibroblasts. These cells exhibited significant reductions in lifespan associated with major abnormalities of the nuclear shape and structure. This is the first report of MAD presenting with confirmed myopathic abnormalities associated with ZMPSTE24 defects, extending the clinical spectrum of ZMPSTE24 gene mutations. Moreover, our results suggest that defective prelamin A processing affects muscle regeneration and development, thus providing new insights into the disease mechanism of prelamin A-defective associated syndromes in general.

Role of sex steroids, intrahepatic fat and liver enzymes in the association between SHBG and metabolic features

SHBG and liver enzymes levels are both associated with the risk of type 2 diabetes. However, the relationship between SHBG with liver enzymes and intrahepatic fat content remain poorly understood.

Reference Values for IGF-I Serum Concentrations: Comparison of Six Immunoassays

Context: Measurement of IGF-I is essential for diagnosis and management of patients with disorders affecting the somatotropic axis. However, even when IGF-I kit manufacturers follow recent consensus guidelines, different kits can give very different results for a given sample. Objectives: We sought to establish normative data for six IGF-I assay kits based on a large random sample of the French general adult population. Subjects and Methods: In a cross-sectional multicenter cohort study, we measured IGF-I in 911 healthy adults (18–90 years) with six immunoassays (iSYS, LIAISON XL, IMMULITE, IGFI RIACT, Mediagnost ELISA, and Mediagnost RIA). Pairwise concordance between assays was assessed with Bland-Altman plots for both IGF-1 raw data and standard deviation scores (SDS), as well as with the percentage of observed agreement and the weighted Kappa coefficient for categorized IGF-I SDS. Results: Normative data included the range of values (2.5–97.5 percentiles) given by the six IGF-I assays according to age group and sex. A formula for SDS calculation is provided. Although the lower limits of the reference intervals of the six assays were similar, the upper limits varied markedly. Pairwise concordances were moderate to good (0.38–0.70). Conclusion: Despite being obtained in the same healthy population, the reference intervals of the six commercial IGF-1 assay kits showed noteworthy differences. Agreement between methods was moderate to good.

Parallel assessment of male reproductive function in workers and wild rats exposed to pesticides in banana plantations in Guadeloupe

BackgroundThere is increasing evidence that reproductive abnormalities are increasing in frequency in both human population and among wild fauna. This increase is probably related to exposure to toxic contaminants in the environment. The use of sentinel species to raise alarms relating to human reproductive health has been strongly recommended. However, no simultaneous studies at the same site have been carried out in recent decades to evaluate the utility of wild animals for monitoring human reproductive disorders. We carried out a joint study in Guadeloupe assessing the reproductive function of workers exposed to pesticides in banana plantations and of male wild rats living in these plantations.MethodsA cross-sectional study was performed to assess semen quality and reproductive hormones in banana workers and in men working in non-agricultural sectors. These reproductive parameters were also assessed in wild rats captured in the plantations and were compared with those in rats from areas not directly polluted by humans.ResultsNo significant difference in sperm characteristics and/or hormones was found between workers exposed and not exposed to pesticide. By contrast, rats captured in the banana plantations had lower testosterone levels and gonadosomatic indices than control rats.ConclusionWild rats seem to be more sensitive than humans to the effects of pesticide exposure on reproductive health. We conclude that the concept of sentinel species must be carefully validated as the actual nature of exposure may varies between human and wild species as well as the vulnerable time period of exposure and various ecological factors.