Hypertriglyceridemia and lower LDL cholesterol concentration in relation to apolipoprotein E phenotypes in myotonic dystrophy

Dyslipidemia in Muscular Dystrophy: A Systematic Review and Meta-Analysis

BACKGROUND

Muscular dystrophies (MDs) are characterized by chronic muscle wasting but also poorly understood metabolic co-morbidities. We have recently shown that Duchenne MD (DMD) patients, dogs and asymptomatic carriers are affected by a new form of dyslipidemia that may exacerbate muscle damage.

OBJECTIVE

We aimed to perform a systematic review and meta-analysis for evidence that other types of MDs are associated with dyslipidemia compared to healthy controls.

METHODS

Search was conducted using MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials for reports that compare plasma/serum lipids from MD patients and controls, and meta-analysis of cross-sectional studies quantifying total cholesterol, high-density lipoprotein, low density lipoprotein and triglycerides was performed.

RESULTS

Out of 749 studies, 17 met our inclusion criteria for meta-analysis. 14 of the 17 studies (82% ) included investigated myotonic dystrophy (DM); other studies were on pseudohypertrophic MD (PMD) or DMD. As a whole, MD individuals had significantly higher levels of circulating total cholesterol (Hedges' g with 95% confidence interval [CI], 0.80 [0.03 - 1.56]; p = 0.04) and triglycerides (Hedges' g with 95% confidence interval [CI], 2.28[0.63 - 3.92]; p = 0.01) compared to controls. Meta-regression analysis showed the percentage of male gender was significantly associated with the difference in total cholesterol (beta = 0.05; 95% CI, - 0.02 to 0.11; p = 0.043) and high-density lipoprotein (beta = - 9.38; 95% CI, - 16.26 to - 2.50; p = 0.028).

CONCLUSIONS

MD is associated with significantly higher circulating levels of total cholesterol and triglycerides. However, caution on the interpretation of these findings is warranted and future longitudinal research is required to better understand this relationship.

Metabolic Alterations in Myotonic Dystrophy Type 1 and Their Correlation with Lipin

Myotonic dystrophy type 1 (DM1) is an autosomal dominant hereditary and multisystemic disease, characterized by progressive distal muscle weakness and myotonia. Despite huge efforts, the pathophysiological mechanisms underlying DM1 remain elusive. In this review, the metabolic alterations observed in patients with DM1 and their connection with lipin proteins are discussed. We start by briefly describing the epidemiology, the physiopathological and systemic features of DM1. The molecular mechanisms proposed for DM1 are explored and summarized. An overview of metabolic syndrome, dyslipidemia, and the summary of metabolic alterations observed in patients with DM1 are presented. Patients with DM1 present clinical evidence of metabolic alterations, namely increased levels of triacylglycerol and low-density lipoprotein, increased insulin and glucose levels, increased abdominal obesity, and low levels of high-density lipoprotein. These metabolic alterations may be associated with lipins, which are phosphatidate phosphatase enzymes that regulates the triacylglycerol levels, phospholipids, lipid signaling pathways, and are transcriptional co-activators. Furthermore, lipins are also important for autophagy, inflammasome activation and lipoproteins synthesis. We demonstrate the association of lipin with the metabolic alterations in patients with DM1, which supports further clinical studies and a proper exploration of lipin proteins as therapeutic targets for metabolic syndrome, which is important for controlling many diseases including DM1.

High-fat diet induced adiposity and insulin resistance in mice lacking the myotonic dystrophy protein kinase

Myotonic dystrophy 1 (MD1) is caused by a CTG expansion in the 3'-unstranslated region of the myotonic dystrophy protein kinase (DMPK) gene. MD1 patients frequently present insulin resistance and increased visceral adiposity. We examined whether DMPK deficiency is a genetic risk factor for high-fat diet-induced adiposity and insulin resistance using the DMPK knockout mouse model. We found that high-fat fed DMPK knockout mice had significantly increased body weights, hypertrophic adipocytes and whole-body insulin resistance compared with wild-type mice. This nutrient-genome interaction should be considered by physicians given the cardiometabolic risks and sedentary lifestyle associated with MD1 patients.

Testosterone and diurnal rhythmicity of leptin, TNF-alpha and TNF-II receptor in insulin-resistant myotonic dystrophy patients

OBJECTIVE

To investigate the leptin and TNF systems in relation to testosterone in insulin resistant myotonic dystrophy (DM1) subjects.

DESIGN AND SUBJECTS

Fasting morning samples and diurnal sampling during 24 h. Forty-two DM1 subjects (20 women and 22 men; age 41.5 (28.5-58.7) y, body mass index (BMI) 23.3 (18.6-29.2) kg/m(2); median and 10th and 90th percentile, respectively). Fifty healthy volunteers (23 women and 27 men; age 42 (27.0-56.9) y, BMI 24.0 (20.7-29.7) kg/m(2)). Nine men with DM1 and nine healthy men participated in diurnal sampling.

MEASUREMENTS

Body composition was measured by bioelectric impedance analysis. Circulating levels of leptin, TNF-alpha, TNFR-II, insulin, testosterone and lipids were measured. The number of CTG triplet repeats was analysed.

RESULTS

Basal as well as median 24 h levels of leptin and TNFR-II were significantly increased in DM1 patients, independent of body fat mass. This was associated with higher insulin and lower testosterone levels in DM1 patients. The genetic defect was related to leptin and TNFR-II levels in DM1 patients.

CONCLUSION

Hyperleptinemia in DM1 is clearly linked to the concomitant hypogonadism. The genetic defect may directly or indirectly contribute to increased leptin levels. Increased exposure of cytokines may contribute to insulin resistance and other hormonal disturbances in DM1.

Increased levels of tPA antigen and tPA/PAI-1 complex in myotonic dystrophy

OBJECTIVE

To assess the fibrinolytic system in myotonic dystrophy (DM1), a disease connected to features of the metabolic syndrome, including a prominent insulin resistance, increased body fat mass, and hypertriglyceridaemia. We hypothesized that abnormalities in the fibrinolytic system are linked to metabolic dysfunction in DM1.

DESIGN

Circulating morning levels of tissue plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1) antigens, tPA/PAI-1 complex, lipids and insulin were determined. Genetic analyses, including calculation of allele size, were performed in all patients. Body fat mass was estimated with bioelectrical impedance analysis.

SETTING

Out-patient clinic in collaboration with Umeå University Hospital.

SUBJECTS

A total of 42 otherwise healthy patients with DM1 (22 men, 20 women; median age 41.5 years) and 50 controls (27 men, 23 women; median age 42.0 years).

MAIN OUTCOME MEASURES

The tPA and PAI-1 antigens, tPA/PAI-1 complex, blood lipids and body fat mass.

RESULTS

The tPA antigen and tPA/PAI-1 complex levels were significantly increased in DM1 patients (P < 0.001 and P < 0.05, respectively) whilst levels of PAI-1 did not differ from controls. Triglyceride levels were increased (P < 0.001) whereas HDL cholesterol levels were lower in DM1 patients (P < 0.05). Body fat mass was increased in DM1 patients (P < 0.001).

CONCLUSIONS

The fibrinolytic system is disturbed in DM1 patients, with increased levels of tPA and tPA/PAI-1 complex but paradoxically unaltered levels of PAI-1, in spite of a severely increased body fat mass. This may imply an abnormal function of adipose tissue in DM1, and calls for further studies of the fibrinolytic system in this disease.bstra

A 10-year study of mortality in a cohort of patients with myotonic dystrophy

OBJECTIVE

To determine the age and causes of death as well as the predictors of survival in patients with myotonic dystrophy (DM).

METHODS

In a longitudinal study, a cohort of 367 patients with definite DM was followed for 10 years.

RESULTS

During the 10-year period, 75 of the 367 DM patients (20%) died. The mean age at death (53.2 years, range 24 to 81) was similar for men and women. Among these 75 patients, 32 (43%) died of a respiratory problem, 15 (20%) of cardiovascular disease, 8 (11%) of a neoplasia, and 8 (11%) died suddenly. The ratio of observed to expected deaths was significantly increased to 56.6 (95% confidence interval [CI] 38.7 to 78.0) for respiratory diseases, 4.9 (95% CI 2.7 to 7.7) for cardiovascular diseases, and 2.5 (95% CI 1.1 to 4.6) for neoplasms. The mean age at death was 44.7 years for the childhood phenotype of DM, 47.8 years for the early-adult, 55.4 years for the adult, and 63.5 years for the mild phenotype (F = 4.8, p = 0.005). The age-adjusted risk of dying was 3.9 (95% CI 1.3 to 11.0) times greater for a patient with a distal weakness and 5.6 (95% CI 2.2 to 14.4) times greater for a patient with proximal weakness as compared with a person without limb weakness.

CONCLUSIONS

Life expectancy is greatly reduced in DM patients, particularly in those with early onset of the disease and proximal muscular involvement. The high mortality reflects an increase in death rates from respiratory diseases, cardiovascular diseases, neoplasms, and sudden deaths presumably from cardiac arrhythmias.

The relation of plasma triglyceride, apolipoprotein B, and high-density lipoprotein cholesterol to postheparin lipoprotein lipase activity is dependent on apolipoprotien E polymorphism

Postheparin plasma (PH)-lipoprotein lipase (LPL) activity has been reported to be a significant correlate of plasma triglyceride and high-density lipoprotein cholesterol (HDL-C) levels. However, some studies have failed to observe these associations. In this regard, apolipoprotein (apo) E polymorphism may play an important role, since the apo E2 isoform has unfavorable effects on the catabolism of triglyceride-rich lipoprotein particles. We have thus examined the relationships between PH-LPL activity and plasma lipoprotein-lipid levels within groups of men classified on the basis of apo E phenotypes, to verify whether apo E polymorphism could alter these associations. In men carrying the apo E2 isoform (n = 12), PH-LPL activity showed a strong negative correlation with plasma triglyceride (r = -.72, P < .01), very-low-density lipoprotein (VLDL) triglyceride ([VLDL-TG] r = -.83, P < .001), and VLDL cholesterol ([VLDL-C] r = -.57, P < .05) levels and a positive correlation with plasma HDL-C (r = .87, P < .001) and HDL2-C (r=.90, P < .001) concentrations. These correlations were also noted for plasma apo B levels (r = -.65, P < .05), VLDL-apo B concentrations (r= -.76, P < .01), and the HDL-C to cholesterol ratio (r = .85, P < .001). In contrast, none of these associations were found in men carrying the apo E4 isoform (n = 11). In men homozygous for the apo E3 isoform (n = 29), PH-LPL activity was only significantly correlated with plasma HDL2-C levels (r = .46, P < .01). Results of the present study indicate that PH-LPL activity is related to plasma triglyceride, VLDL-TG, VLDL-C, VLDL-apo B, apo B, and HDL-C levels and the HDL-C to cholesterol ratio in men carrying the apo E2 isoform, but not in men homozygous for the apo E3 isoform or among apo E4 carriers. Thus, apo E polymorphism appears to modulate the effect of variation in PH-LPL activity on the plasma lipoprotein profile.

Myotonic dystrophy: linkage with apolipoprotein E and estimation of the gene carrier status with genetic markers

The genes for myotonic dystrophy (MD) and for apolipoprotein E (ApoE) belong to a chromosome 19 synthenic group of markers. A familial linkage analysis between MD and ApoE was performed using the J Ott LIPED program (IBM PC/XT, April 1984) to estimate the genetic distance between these 2 genes. Of a total of 136 individuals in 11 MD families, 81 were confirmed to be affected by the disease and 41 were asymptomatic. ApoE phenotypes were determined in 115 of these 122 individuals. No recombinant was observed out of 74 meioses which were informatives for both MD and the ApoE isoproteins. A global maximal lod score Z of 19.00 was obtained at the recombination fraction theta = 0. The upper theta value at the confidence interval corresponding to the peak lod score (Z max) - 1 was 0.03. This suggests that the loci for MD and ApoE are at a distance of 0 to 0.03 Morgan. Since ApoE and apolipoprotein C2 (ApoC2) have been shown by others to be about 40 kb apart, our data are therefore consistent with the distance estimate of 0.02 Morgan reported between MD and ApoC2. The D19S19 (LDR152) polymorphic DNA sequence is also tightly linked to MD on chromosome 19. The segregation of ApoE isoproteins and of ApoC2 and D19S19 DNA polymorphism was utilized for evaluating the probability for individuals at risk of inheriting the disease gene in MD families. Data are presented on 3 families to emphasize the usefulness of genetic markers to estimate the MD gene carrier status of asymptomatic individuals and also for those presenting a partial syndrome. The limitations of such approach are also discussed.