No abstract

Familial hypomagnesaemia with hypercalciuria and nephrocalcinosis (FHHNC, MIM 248250) is a complex renal tubular disorder characterised by hypomagnesaemia, hypercalciuria, advanced nephrocalcinosis, hyposthenuria and progressive renal failure. The mode of inheritance is autosomal recessive. A primary defect in the reabsorption of magnesium in the medullary thick ascending limb of the loop of Henle (mTAL) has been proposed to be essential in FHHNC pathophysiology. To identify the underlying genetic defect we performed linkage analysis in eight families, including three with consanguineous marriages. We found linkage to microsatellite markers on chromosome 3q27 with a maximum two-point lod score (Z max ) of 5.208 for D3S3530 without evidence for genetic heterogeneity. Haplotype analysis revealed crucial recombination events reducing the critical interval to 6.6 cM. Recently, mutations in the gene PCLN-1, mapping to 3q27 and coding for paracellin-1, were identified by Simon et al (1999) as the underlying genetic defect in FHHNC. Paracellin-1 represents a renal tight junction protein predominantly expressed in the TAL. Mutational analysis in our patient cohort revealed eight different mutations in the PCLN-1 gene, within six novel mutations. In seven of 13 mutant alleles we detected a Leu151 substitution without evidence for a founder effect. Leu151 is a residue of the first extracellular loop of paracellin-1, the part of the protein expected to bridge the intercellular space and to be important for paracellular conductance. This study confirms the implication of paracellin-1 defects in FHHNC and points to a predominant role of this protein in the paracellular reabsorption of divalent cations in the TAL.

The long-term consequences of cardiac alterations in children with chronic renal failure (CRF) and after renal transplantation (TX) are largely unknown. Studies in adults with end-stage renal disease (ESRD) assume that the fate of many pediatric patients is determined by a high cardiovascular morbidity and mortality. This review describes clinical manifestations, pathophysiology, cardiac function and structure, and management of heart disease in children with CRF and post transplant. Echocardiography and Doppler ultrasonography allow differentiation of three functional disturbances: hypercirculation, systolic left ventricular (LV) dysfunction, and diastolic LV dysfunction, in addition to analysis of LV size and myocardial mass. From adult studies LV hypertrophy is recognized as an early prognostic marker of cardiovascular disease. It is present in about half of children with ESRD and after TX. It may regress, at least in part, by control of hypertension, hypervolemia, and anemia. Experimental studies have shown that, independent of these hemodynamic complications, uremia is associated with structural abnormalities of the heart, which were also described in adult patients with ESRD. These lesions consist mainly of hypertrophy of cardiomyocytes, interstitial fibrosis, and vascular changes (rarefied capillaries, thickened arteriolar walls). Cardiac complications in children with CRF and after TX deserve regular clinical and echocardiographic monitoring in order to minimize later cardiovascular morbidity by appropriate treatment.

Abstract-To assess the prevalence and characteristics of physiological circadian (24-hour) and ultradian (12-, 8-, and 6-hour) rhythms of mean arterial blood pressure (BP) and heart rate (HR), we analyzed 24-hour ambulatory BP profiles from 938 healthy school children aged 5 to 18 years. Cosine harmonics were fitted by Fourier analysis, and an amplitude and acrophase (time of peak) were calculated for each rhythm. Ninety percent of children displayed circadian rhythmicity of BP, independent of age, whereas circadian HR rhythmicity decreased with puberty from 96% to 87% (PϽ0.0001). Puberty had marked effects on the prevalence of ultradian rhythmicity: 12-and 6-hour rhythms increased for BP (27% to 47%, PϽ0.0001; 18% to 25%, Pϭ0.01) and HR (36% to 47%, 17% to 31%, both Pϭ0.001), whereas 8-hour BP rhythms decreased (34% to 23%, Pϭ0.002). Median amplitudes were 10.1, 5.9, 5.6, and 5.2 mm Hg for the 24-, 12-, 8-, and 6-hour BP rhythms, respectively, and 13.4, 7.7, 6.8, and 6.4 bpm for HR. The acrophase occurred at approximately 14:00 hours, 8:00 hours, 5:30 hours, and 2:00 hours (military time) for the four BP rhythms, and at 13:30 hours, 08:30 hours, 01:50 hours, and 02:00 hours for HR. For the combined curve, the peak-trough difference was 25.9 mm Hg and 35 bpm for BP and HR, respectively, with the peaks occurring at 13:50 hours and 13:10 hours. There was marked association between BP and HR rhythms, both for prevalence (PϽ0.0001 for coupling of BP and HR rhythms of the same period length) and timing, with a median time lag of BP after HR acrophase of only 21, 16, 13, and 5 minutes for the four rhythms, respectively.