Probing the factor structure of metabolic syndrome in Sardinian genetic isolates

BACKGROUND AND AIMS

Owing to the multiplicity of the key components of metabolic syndrome (MetS), its diagnosis is very complex. The lack of a unique definition is responsible for the prevalence variability observed among studies; therefore, a definition based on continuous variables was recommended. The aim of this study was to compare competing models of the MetS factor structure for selecting the one that explains the best clustering pattern and to propose an algorithm for computing MetS as a continuous variable.

METHODS AND RESULTS

Data were from isolated Sardinian populations (n = 8102). Confirmatory factor analysis (CFA) and two-group CFA by gender were performed to evaluate the sex-specific factor structure of MetS. After selecting the best model, an algorithm was obtained using factor loadings/residual variances. The quality of the MetS score was evaluated by the receiver operating characteristics curve and the area under the curve. Cross-validation was performed to validate the score and to determine the best cut point. The best fit model was a bifactor one with a general factor (MetS) and three specific factors (f1: obesity/adiposity trait; f2: hypertension/blood pressure trait; and f3: lipid trait). Gender-specific algorithms were implemented to obtain MetS scores showing a good diagnostic performance (0.80 specificity and 0.80 sensitivity for the cut point). Furthermore, cross-validation confirmed these results.

CONCLUSION

These analyses suggested that the bifactor model was the most representative one. In addition, they provided a score and a cut point that are both clinically accessible and interpretable measures for MetS diagnosis and likely useful for evaluating the association with adverse cardiovascular disease and diabetes and for investigating the MetS genetic component.

Charcot-Marie-Tooth disease type 2 associated with mutation of the myelin protein zero gene

Charcot-Marie-Tooth disease (CMT), or hereditary motor and sensory neuropathy (HMSN), is a clinically and genetically heterogeneous condition. Mutations of the myelin protein zero (MPZ) gene have been associated with CMT1B, Dejerine-Sottas disease, and congenital hypomyelination, which are inherited demyelinating neuropathies characterized by different clinical severity. HMSN type II (HMSN II) or CMT2, the axonal form of CMT, is genetically heterogeneous. Linkage to 1p35-p36 (CMT2A), 3q (CMT2B), and 7p (CMT2D) chromosomes has been reported in the disease; however, most HMSN II families do not link to any of the reported loci. In a large HMSN II Sardinian family, we found a missense mutation in the chromosome 1q MPZ gene. This Ser44Phe mutation was located in exon 2 and was present in the heterozygous state in all affected individuals. This is the first example of an HMSN II family showing an MPZ point mutation. The MPZ gene Ser44Phe mutation found in the HMSN II family presented in this study suggests that genetic analysis of HMSN II families should also include the MPZ gene, previously not considered to be involved in the axonal form of HMSN.

Occurrence and clinical relevance of an interleukin-4 gene polymorphism in patients with multiple sclerosis

An epistatic gene interaction has been advocated to explain disease susceptibility in multiple sclerosis (MS). Cytokine genes are possible candidates due to the central role played by cytokines in the regulation of the immune-mediated pathogenetic process leading to central nervous system demyelination in these patients. Since interleukin (IL)-4 gene polymorphisms have been associated with immune-mediated diseases, we have analysed the relationship between a variable number of tandem repeat polymorphism of the IL-4 gene and clinical and physiological features of 256 sporadic MS patients and 146 healthy controls. Genotype frequencies were similar between the MS group and healthy controls. However, in MS patients a positive and significant correlation (r = 0.91; p < 0.001) was found between the carriage rate of the IL-4 B1 allele (from 0.21 to 0.36) and age of disease onset. No association was found between IL-4 alleles and disease progression, sex or ethnic background of the patients. Our results show that the IL-4 B1 allele is associated with late onset of MS and therefore might represent a modifier of age of onset rather than a susceptibility factor for patients with MS.

A novel point mutation in the peripheral myelin protein 22 (PMP22) gene associated with Charcot-Marie-Tooth disease type 1A

We studied the peripheral myelin protein gene PMP-22 in a large Sardinian family with Charcot-Marie-Tooth disease type 1A (CMT1A), in which the duplication commonly found in CMT1A was absent, but with evidence of linkage on chromosome 17. Sequencing of DNA and cDNA showed a missense point mutation G368-->T in exon 5 of PMP22, predicted to determine a valine for glycine substitution at codon 107, which could be plotted in the center of the PMP22 protein putative transmembrane domain III. Using sequence-specific oligonucleotide probes (SSOP), we found the point mutation in all affected CMT1A subjects but not in healthy family members or in 314 chromosomes of controls, thus indicating that the G368-->T point mutation is not a polymorphism. In the hypothetical model of PMP22, the amino acid at position 107 plots deeply into alpha-helical transmembrane domain III, a domain where point mutations have never previously been found. Although the same mutation was present in all CMT1A subjects examined, clinical findings showed a different stereotyped pattern in relation to the generation examined, for a progressive increase in severity and an earlier onset from the first to the third generation examined. Molecular analysis suggests that CMT1A disease in this family is due to the G368-->T point mutation, although other mechanisms may account for the clinical variability in the members of different generations.