Double-blind, randomized feedback control fails to improve the hypocholesterolemic effect of a plant-based low-fat diet in patients with moderately elevated total cholesterol levels.

OBJECTIVE: To determine whether the cholesterol-lowering effect of a plant-based low-fat diet can be improved by a flexible control design that controls the extent of fat reduction based on the individual response of blood cholesterol. DESIGN: Randomized, double-blind intervention study. SETTING: A hotel in Prerow, Germany. SUBJECTS: A total of 32 participants (21 female and 11 male participants) with total cholesterol level > 5.7 mmol/l. INTERVENTION: The control group consumed a plant-based low-fat diet with constantly 20% of energy as fat; the intervention group received a diet with either 20 or 15% of energy as fat, depending on the serum cholesterol response of the preceding week. A flexible control design based on the individual cholesterol response during a run-in period of 1 week was used within a low-fat intervention. RESULTS: During the run-in period, the consumption of a plant-based low-fat diet led to a reduction in total cholesterol by 18+/-6 mmol/l (P < 0.001), in LDL cholesterol by 19+/-9 mmol/l (P < 0.001) and triglycerides by 13+/-3 mmol/l (P < 0.001). During the feedback control period, an additional reduction in total cholesterol by 13+/-8 (P < 0.001) and in LDL cholesterol by 17+/-11 (P < 0.001) was observed compared to 15+/-15 and 7+/-18 in the control group. The effect of an additional feedback control was only marginal and not statistically significant compared to the effect of the low-fat diet alone. CONCLUSIONS: On a level of fat intake already reduced to 20% of energy, the use of a feedback control to adapt the fat content of the diet depending on the individual serum cholesterol response was not more effective in reducing blood cholesterol levels than a plant-based low-fat diet alone.

Spectrum of mutations in the major human skeletal muscle chloride channel gene (CLCN1) leading to myotonia.

Autosomal dominant myotonia congenita and autosomal recessive generalized myotonia (GM) are genetic disorders characterized by the symptom of myotonia, which is based on an electrical instability of the muscle fiber membrane. Recently, these two phenotypes have been associated with mutations in the major muscle chloride channel gene CLCN1 on human chromosome 7q35. We have systematically screened the open reading frame of the CLCN1 gene for mutations by SSC analysis (SSCA) in a panel of 24 families and 17 single unrelated patients with human myotonia. By direct sequencing of aberrant SSCA conformers were revealed 15 different mutations in a total of 18 unrelated families and 13 single patients. Of these, 10 were novel (7 missense mutations, 2 mutations leading to frameshift, and 1 mutation predicted to affect normal splicing). In our overall sample of 94 GM chromosomes we were able to detect 48 (51%) mutant GM alleles. Three mutations (F413C), R894X, and a 14-bp deletion in exon 13) account for 32% of the GM chromosomes in the German population. Our finding that A437T is probably a polymorphism is in contrast to a recent report that the recessive phenotype GM is associated with this amino acid change. We also demonstrate that the R894X mutation may act as a recessive or a dominant mutation in the CLCN1 gene, probably depending on the genetic background. Functional expression of the R894X mutant in Xenopus oocytes revealed a large reduction, but not complete abolition, of chloride currents. Further, it had a weak dominant negative effect on wild-type currents in coexpression studies. Reduction of currents predicted for heterozygous carriers are close to the borderline value, which is sufficient to elicit myotonia.

Molecular and genetic characterisation of German families with paramyotonia congenita and demonstration of founder effect in the Ravensberg families.

Eighteen German families with a history of paramyotonia congenita (PC) were characterised by genetic and mutational analysis at the SCN4A locus, which encodes the alpha-subunit of the adult skeletal muscle sodium channel. We concentrated our analysis primarily on these families to test the hypothesis that a predominance of one common mutation occurs in all German PC families and that this mutation arose in a common ancestor originating in the North-West of the country. The present eighteen PC families exhibit two different mutations (R1448C and R1448H) on various SCN4A dinucleotide repeat haplotypes and therefore the majority of the mutations probably occurred independently. However, the R1448H mutation is extremely frequent in the North-West of Germany (Ravensberger Land) on a specific SCN4A microsatellite haplotype, indicating a founder effect within this subpopulation. Our results suggest that the R1448C/R1448H mutations are by far the most common to be associated with the PC phenotype in the German population.

Genomic organization of the human muscle chloride channel CIC-1 and analysis of novel mutations leading to Becker-type myotonia.

The muscle chloride channel CIC-1 regulates the electric excitability of the skeletal muscle membrane. Mutations in the gene encoding this chloride channel (CLCN1) are responsible for both human purely myotonic disorders, autosomal recessive generalized myotonia (Becker's disease, GM) and autosomal dominant myotonia congenita (Thomsen's disease, MC). We now show that the protein-coding sequence of the CLCN1 gene is organized into 23 exons. The CIC-1 upstream region contains a canonical TATA box, several consensus binding sites for myogenic transcription factors and two other putative regulatory elements. SSCA analysis of a German GM family revealed that affected members are compound heterozygotes having two novel mutations. G979A affects a splice consensus site at the end of exon 8, and G1488T in exon 14 leads to a replacement of a positive charge in a highly conserved putative transmembrane domain (R496S). Functional expression of R496S cRNA in Xenopus oocytes did not yield detectable currents. It neither suppressed wild-type currents in a co-expression assay, confirming it as a recessive mutation.