Our findings demonstrate that in Bartter's and Gitelman's syndromes, it may not be uncommon to see mutations in several causative transporter genes.

Hypokalemic metabolic tubulopathy, such as in Bartter syndrome and Gitelman syndrome, is caused by the dysfunction of renal electrolyte transporters. Despite advances in molecular genetics with regard to hypokalemic metabolic tubulopathy, recent reports have suggested that the phenotype-genotype correlation is still confusing, especially in classic Bartter and Gitelman syndromes. We report here two Japanese patients who suffered from clinically diagnosed classic Bartter syndrome but who presented hypocalciuria. Hypocalciuria is generally believed to be a pathognomonic finding of NCCT malfunction. To better understand the genotype-phenotype correlation in these two cases, we screened four renal electrolyte transporter genes [Na-K-2Cl cotransporter (NKCC2), renal outer medullary K channel (ROMK), Cl channel Kb (ClC-Kb), and Na-Cl cotransporter (NCCT)] by the PCR direct sequencing method. We identified three ClC-Kb allelic variants, including two new mutations (L27R and W610X in patient 1 and a G to C substitution of a 3' splice site of intron 2 and W610X in patient 2). We did not find any mutations in the other three genes. Our present data suggest that some ClC-Kb mutations may affect calcium handling in renal tubular cells.

All of these data suggest that Trp64Arg mutation of the beta3-AR gene might affect obesity and HDL metabolism in obese boys. In contrast, C161T mutation of the PPARgamma gene, by itself, is unlikely to influence obesity, lipid metabolism or plasma leptin levels.

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Cholesteryl ester transfer protein (CETP) is thought to regulate plasma HDL. Patients with CETP deficiency caused by mutation of the CETP gene [D442G; a missense mutation (Asp4423 Gly)] have been reported to show high plasma HDL levels. However, there are no data available on children with D442G. To determine the effects of plasma CETP and CETP gene mutation (D442G) on lipids and lipoproteins in children, we screened children by PCR and restriction fragment length polymorphism analysis of the CETP gene. Plasma lipids, apolipoproteins, and CETP mass levels were also determined. In the current study, 22 children with D442G were found (21 heterozygotes and a homozygote). A homozygous child showed high plasma HDL level and very low plasma CETP mass. In heterozygous children, plasma concentrations of HDL cholesterol, apo A-I and apo A-II were not increased, whereas plasma CETP mass was significantly decreased. Plasma CETP mass in heterozygous children was correlated with plasma concentrations of total cholesterol, LDL cholesterol, and apo B. Plasma CETP mass in children without D442G was not correlated with the plasma concentration of any lipid or apolipoprotein. All of these data suggest that the D442G mutation, by itself, might not affect HDL metabolism in children. The CETP mass required for efficient HDL-cholesteryl ester clearance in children may be less than that in older subjects. Esterification of cholesterol from peripheral tissues and subsequent transfer of CE from HDL to other lipoproteins are key steps in reverse cholesterol transport, i.e. transport from peripheral cells to the liver for excretion (1, 2). In humans, extracellular cholesterol is esterified by the action of LCAT, and the CE generated is transferred to the liver by two known pathways: 1) uptake of HDL particles by the liver (3, 4), and 2) uptake of HDL CE by LDL receptor in the liver via transfer of HDL-CE to VLDL and LDL, in a process mediated by CETP (1, 2, 5). Most LCAT and CETP are associated with HDL particles in human plasma (6, 7). Cholesterol esterification in HDL by LCAT increases the size of HDL particles, and the transfer of CE from HDL particles reduces the size of HDL. Thus, the size of HDL particles reflects the net rate of CE generation on and CE transfer from HDL particles. Furthermore, we have shown in previous studies that the function of HDL, as well as the particle size, is strongly affected in the presence of LCAT or CETP deficiency (8, 9). These findings, taken together, suggest that LCAT and CETP play a central role in maintaining the antiatherogenic nature of HDL.To date, several common polymorphisms have been reported in the CETP gene (10 -12). Most are located within intronic regions and do not appear to affect either the secretion or the function of CETP. Two mutations, an intron 14 splice donor site mutation (Int14A) and a missense mutation within exon 15 (D442G), have been reported in Japanese subjects with high HDL-C levels (Ͼ100 mg/dL) (13-15). These mutations affect the structure and function of CETP and are ...