Marie-Thérèse Berthier

The interleukin 6 –174G/C Polymorphism is associated with indices of obesity in men

AbstractObesity represents an expansion of adipose tissue (AT) mass and is closely related to insulin resistance and cardiovascular disease. Several hormonal signals have been shown to originate from AT, one of them being interleukin 6 (IL6), for which one third of circulating levels is accounted for by AT. To study the impact of the IL6 –174G/C polymorphism on obesity-related phenotypes, we genotyped a cohort of 270 French-Canadian men from the greater Quebec City area selected to cover a wide range of body fatness values. The IL6 –174G allele was more commonly observed among lean subjects (body mass index <25kg/m2, χ2 = 7.27, P = 0.007 or waist-line <100cm, χ2 = 6.63, P = 0.01). When men were subdivided according to insulin and glucose levels at 180min following the glucose load, using 160pmol/l and 4.6mmol/l, respectively, as cutoff points, the –174G allele was more frequently observed in groups with low concentrations of either insulin or glucose, P = 0.03 and P = 0.01, respectively. When comparisons between genotype groups were performed, –174G/G homozygotes presented the lowest waist circumference (P < 0.05). In summary, this study showed that, in men, the IL6 –174G/C polymorphism is associated with some indices of body composition and parameters of glucose and insulin homeostasis.

Molecular screening of the microsomal triglyceride transfer protein : association between polymorphisms and both abdominal obesity and plasma apolipoprotein B concentration

AbstractMicrosomal triglyceride transfer protein (MTP) plays a critical role in the assembly of lipoproteins. The aim of this study was first to seek new MTP gene variants and then to verify whether MTP gene polymorphisms were associated with plasma lipoprotein/lipid levels in men with visceral obesity. Molecular screening of the MTP gene revealed 11 polymorphisms. The carriers of the c.933A allele and c.1151C allele or –400A/A homozygotes were characterized by increased levels of abdominal visceral adipose tissue (AT) measured by computed tomography (P=0.02, P=0.04, P=0.03, respectively). After dividing each genotype group into subgroups using 130 cm2 as a cutoff point for visceral AT, significantly higher low-density lipoprotein (LDL)-apolipoprotein B (apoB) concentrations were found in obese men bearing the c.891G allele, the –400 T allele, as well as for 282G/G homozygotes, 933C/C homozygotes, and 1151A/A homozygotes when compared to their lean counterparts. Haplotypes were not associated with phenotypes under study. In conclusion, some MTP gene polymorphisms in the French Canadian population are associated with the amount of abdominal visceral AT and plasma LDL-apoB concentrations.

Hypersuccinylacetonaemia and normal liver function in maleylacetoacetate isomerase deficiency

Background A high level of succinylacetone (SA) in blood is a sensitive, specific newborn screening marker for hepatorenal tyrosinemia type 1 (HT1, MIM 276700) caused by deficiency of fumarylacetoacetate hydrolase (FAH). Newborns with HT1 are usually clinically asymptomatic but show liver dysfunction with coagulation abnormalities (prolonged prothrombin time and/or high international normalised ratio). Early treatment with nitisinone (NTBC) plus dietary restriction of tyrosine and phenylalanine prevents the complications of severe liver disease and neurological crises. Methods and results Six newborns referred for hypersuccinylacetonaemia but who had normal coagulation testing on initial evaluation had sequence variants in the GSTZ1 gene, encoding maleylacetoacetate isomerase (MAAI), the enzyme preceding FAH in tyrosine degradation. Initial plasma SA levels ranged from 233 to 1282 nmol/L, greater than normal (<24 nmol/L) but less than the initial values of patients with HT1 (16 944–74 377 nmol/L, n=15). Four individuals were homozygous for c.449C>T (p.Ala150Val). One was compound heterozygous for c.259C>T (p.Arg87Ter) and an intronic sequence variant. In one, a single heterozygous GSTZ1 sequence variant was identified, c.295G>A (p.Val99Met). Bacterial expression of p.Ala150Val and p.Val99Met revealed low MAAI activity. The six individuals with mild hypersuccinylacetonaemia (MHSA) were not treated with diet or nitisinone. Their clinical course has been normal for up to 13 years. Conclusions MHSA can be caused by sequence variants in GSTZ1. Such individuals have thus far remained asymptomatic despite receiving no specific treatment.

Newborn Screening By Tandem Mass Spectrometry: Impacts, Implications and Perspectives

There are over 6000 inherited human diseases described in the McKusick Online Mendelian Inheritance in Man database (OMIM)(McKusick-Nathans Institute of Genetic Medicine, 2011). They show a wide range of variability in frequency, severity, age of onset, diagnostic and treatment approaches. A subset of diseases induce severe metabolic disturbances in the newborn that can lead to irreversible damage and illnesses. For some of those, there is a treatment that prevents such damages as long as it is initiated early after birth. For these diseases, population-based newborn screening has been proposed, developed and implemented in many countries albeit at different rates and based on different criteria. Even if those diseases are rare, the burden that is prevented if treated early has been shown to be cost-effective as it is larger than the cost of systematic screening and treatment of the cases identified (Venditti et al., 2003). Different analytical methods have been deployed since the 1960’s to detect abnormal levels of specific metabolites or hormones in the newborn’s blood with sufficient reliability and low cost to allow their use as screening methods (see 1.1). We will describe the tremendous impact that tandem mass spectrometry has had in the field of newborn screening for inherited diseases in the recent decade. After a brief history of newborn screening, we will describe the classical WHO criteria for population-based screening for disease, summarize impacts of tandem mass spectrometry in this field. Then, we will describe the laboratory workflow, the pre-examination, examination, and postexamination aspects of MS/MS-based newborn screening, its advantages and limitations. Other issues will also be reviewed including sample and data management, revision of screening criteria and future perspectives for MS/MS in population-based screening.

Effect of the factor VII R353Q missense mutation on plasma apolipoprotein B levels: impact of visceral obesity

AbstractAn atherogenic dyslipidemia, characterized by increased plasma triglyceride and apolipoprotein (apo) B levels, low HDL-cholesterol concentrations and the development of small, dense LDL particles has been associated with the presence of abdominal-visceral obesity. Visceral obesity is also associated with a hypercoagulate state and elevated concentrations of procoagulant factors such as factor VII. Moreover, it is known that some genetic variants in the gene encoding factor VII alter its activity and concentration, and consequently these variants may have an impact on atherosclerosis development. The objective of this study was to verify whether the factor VII R353Q polymorphism contributes to predict the risk of an atherogenic dyslipidemia in absence and in the presence of visceral obesity. A sample of 299 French-Canadian men, selected in order to cover a wide range of body fatness values, participated in this study. We observed that the R353 allele was more commonly observed among men characterized by apo B levels below 1.09 g/l than among men with apo B levels greater or above this threshold value (allele frequency of 92.1 vs 85.4%, χ2=6.18, P=0.01). Multivariate analyses further showed that the genotype R353/R353 was associated with a lower risk to exhibit atherogenic concentrations of total-apo B (≥1.09 g/l) and LDL apo B (≥0.95 g/l) before (odds ratio: 0.47, 95%CI=0.27–0.90, P=0.02; odds ratio:0.46, 95%CI=0.25–0.85, P=0.01, respectively) and after adjustments for age and visceral AT (odds ratio:0.49, 95%CI=0.24–0.91, P=0.02; odds ratio: 0.44, 95%CI=0.23-0.85, P=0.01, respectively). When the two genotype groups were further divided on the basis of visceral adipose tissue (AT) accumulation using a cutoff point of 130 cm2, we observed that R353/R353 homozygotes with low visceral AT were characterized by a more favorable lipoprotein-lipid profile, mainly lower total-cholesterol, total-apo B, and LDL-apo B levels compared with R353/R353 homozygotes with high levels of visceral AT. In contrast, irrespective of obesity, plasma lipid levels among carriers of the Q353 allele were similar to those of viscerally obese men homozygous for the R353 allele. In conclusion, results of the present study suggest that the factor VII R353 allele is associated with lower concentrations of plasma apo B levels. However, the presence of visceral obesity abolishes this effect. Further studies will be necessary to confirm this association and the mechanism involved.

Mildly elevated succinylacetone and normal liver function in compound heterozygotes with pathogenic and pseudodeficient FAH alleles

Background A high level of succinylacetone (SA) in blood is a sensitive, specific marker for the screening and diagnosis of hepatorenal tyrosinemia (HT1, MIM 276700). HT1 is caused by mutations in the FAH gene, resulting in deficiency of fumarylacetoacetate hydrolase. HT1 newborns are usually clinically asymptomatic, but have coagulation abnormalities revealing liver dysfunction. Treatment with nitisinone (NTBC) plus dietary restriction of tyrosine and phenylalanine prevents the complications of HT1 Observations Two newborns screened positive for SA but had normal coagulation testing. Plasma and urine SA levels were 3–5 fold above the reference range but were markedly lower than in typical HT1. Neither individual received nitisinone or dietary therapy. They remain clinically normal, currently aged 9 and 15 years. Each was a compound heterozygote, having a splicing variant in trans with a prevalent “pseudodeficient” FAH allele, c.1021C > T (p.Arg341Trp), which confers partial FAH activity. All newborns identified with mild hypersuccinylacetonemia in Québec have had genetic deficiencies of tyrosine degradation: either deficiency of the enzyme preceding FAH, maleylacetoacetate isomerase, or partial deficiency of FAH itself. Conclusion Compound heterozygotes for c.1021C > T (p.Arg341Trp) and a severely deficient FAH allele have mild hypersuccinylacetonemia and to date they have remained asymptomatic without treatment. It is important to determine the long term outcome of such individuals.

Newborn Screening for Hereditary Tyrosinemia Type I in Québec: Update

Hereditary tyrosinemia type I (HTI) is a rare autosomal recessive disorder caused by a fumarylacetoacetate hydrolase (FAH) deficiency. If untreated, its acute form is characterized by hepatic failure, renal dysfunction and neurological crisis, and may lead to death. Due to a genetic founder effect in the French-Canadian population, the prevalence of HTI is increased in the province of Quebec (1/19 819), with the IVS12 + 5G>A (1062 + 5G>A) splice site mutation responsible for more than 90% of mutated alleles. Universal newborn screening for (HT1) was thus established in 1970, and close to four million infants have been tested so far, allowing to identify 185 of the 190 affected newborns. During the 1970-1997 period, 2,249,000 newborns were screened at 3-7 days of life on dried filter paper blood spots by tyrosine (Tyr) concentration followed by indirect colorimetric semi-quantitative and quantitative (Q) succinylacetone (SA) testing (red blood cells δ-aminolevulinate dehydratase inhibition), with immunoreactive FAH as the confirmatory test. This approach allowed to identify 118 of 123 affected newborns. In 1998, owing to earlier hospital discharge and increased rate of breastfeeding, four cases were missed within the same year as the discriminating power of blood Tyr became inadequate. Thus, the screening algorithm was modified: indirect semi-quantitative SA measurement became the first-tier test between 1998 and 2014, and direct SA measurement by tandem mass spectrometry (MS/MS) was implemented in 2014, followed by indirect quantitative SA measurement as second tier test. Confirmation is performed by plasmatic amino acid profile and molecular testing. During the 1998-2016 period, more than 1,5 million neonates have been tested (90% sampled between 24 and 48 h of life): 67 of the 67 HTI cases were identified. Both indirect and direct SA measurement as the initial HTI screening test proved to be highly sensitive and specific, with positive and negative predicting value of 79% and 100% respectively.