Non-anemic homozygous beta(o) thalassemia in an African-American family: association of high fetal hemoglobin levels with beta thalassemia alleles.

We have studied a four-generation (23 subjects) African-American family with beta(o) thalassemia and high fetal hemoglobin (HbF) levels. The beta(o) thalassemia in this family is due to the splicing site mutation, beta IVS2+1G-->A, that leads to aberrant mRNA processing and the absence of beta globin. Two members of this family are homozygous for beta(o) thalassemia and are non-anemic. All family members who are heterozygous for the beta IVS2+1G-->A mutation have elevated HbF, with the exception of two individuals who also have severe alpha-globin chain deficiency. We excluded linkage with the hereditary persistence of fetal hemoglobin loci on chromosomes 6 and X. We also excluded the presence of all previously described determinants in the beta globin gene cluster associated with elevated HbF production. One thalassemia allele is in the Cameroon-like (HS2)/Benin-like beta globin gene cluster haplotype, and the other is in the Senegal-like (HS2)/Benin-like beta globin gene cluster haplotype. We speculate that in the homozygotes, those erythroid cells that express low to absent levels of gamma globin are selectively destroyed. In contrast, in the heterozygotes, the presence of the normal beta globin allele would ameliorate the globin chain imbalance and thus allow survival of erythroid cells that express the abnormal transcript, leading to a typical beta(o) thalassemia phenotype. Thus, the heterocellular gamma globin expression together with in vivo preferential survival of HbF-containing erythroid cells ameliorates Cooley's anemia in the beta(o) thalassemia homozygotes. It remains to be determined what sequences linked to each thalassemia allele and what trans-acting factors contribute to high HbF levels.

Effect of ramipril vs amlodipine on renal outcomes in hypertensive nephrosclerosis: a randomized controlled trial.

CONTEXT: Incidence of end-stage renal disease due to hypertension has increased in recent decades, but the optimal strategy for treatment of hypertension to prevent renal failure is unknown, especially among African Americans. OBJECTIVE: To compare the effects of an angiotensin-converting enzyme (ACE) inhibitor (ramipril), a dihydropyridine calcium channel blocker (amlodipine), and a beta-blocker (metoprolol) on hypertensive renal disease progression. DESIGN, SETTING, AND PARTICIPANTS: Interim analysis of a randomized, double-blind, 3 x 2 factorial trial conducted in 1094 African Americans aged 18 to 70 years with hypertensive renal disease (glomerular filtration rate [GFR] of 20-65 mL/min per 1.73 m(2)) enrolled between February 1995 and September 1998. This report compares the ramipril and amlodipine groups following discontinuation of the amlodipine intervention in September 2000. INTERVENTIONS: Participants were randomly assigned to receive amlodipine, 5 to 10 mg/d (n = 217), ramipril, 2.5 to 10 mg/d (n = 436), or metoprolol, 50 to 200 mg/d (n = 441), with other agents added to achieve 1 of 2 blood pressure goals. MAIN OUTCOME MEASURES: The primary outcome measure was the rate of change in GFR; the main secondary outcome was a composite index of the clinical end points of reduction in GFR of more than 50% or 25 mL/min per 1.73 m(2), end-stage renal disease, or death. RESULTS: Among participants with a urinary protein to creatinine ratio of >0.22 (corresponding approximately to proteinuria of more than 300 mg/d), the ramipril group had a 36% (2.02 [SE, 0.74] mL/min per 1.73 m(2)/y) slower mean decline in GFR over 3 years (P =.006) and a 48% reduced risk of the clinical end points vs the amlodipine group (95% confidence interval [CI], 20%-66%). In the entire cohort, there was no significant difference in mean GFR decline from baseline to 3 years between treatment groups (P =.38). However, compared with the amlodipine group, after adjustment for baseline covariates the ramipril group had a 38% reduced risk of clinical end points (95% CI, 13%-56%), a 36% slower mean decline in GFR after 3 months (P =.002), and less proteinuria (P<.001). CONCLUSION: Ramipril, compared with amlodipine, retards renal disease progression in patients with hypertensive renal disease and proteinuria and may offer benefit to patients without proteinuria.

Homocysteine elevation in sickle cell disease.

OBJECTIVE: Ischemic complications are common in patients with sickle cell disease. Hyperhomocysteinemia is a risk factor for arteriosclerosis and venous thrombosis, and given the propensity of patients with sickle cell disease to develop ischemic complications, we hypothesized that they might have elevated plasma homocysteine concentrations. METHODS: Plasma concentrations of homocysteine, vitamin B12 and folate were measured in 49 adults with sickle cell disease and 16 normotensive Black controls. All subjects with sickle cell disease had been prescribed folic acid 1 mg by mouth daily. RESULTS: The median plasma concentration of homocysteine of subjects with sickle cell disease was approximately 1.5-fold higher than that of controls (p=0.0008). This difference persisted, even when subjects with renal insufficiency were excluded. Plasma folate levels were 1.5-fold higher in subjects with sickle cell disease than in controls (p=0.0498). There was no significant difference in plasma vitamin B12 concentrations between the two groups. There was no difference in plasma homocysteine concentrations between transfused and non-transfused sickle cell subjects. CONCLUSIONS: Patients with sickle cell disease have elevated plasma concentrations of homocysteine in spite of elevated plasma folate levels and vitamin B12 concentrations similar to those observed in controls. Based on these data, we hypothesize that the concentration of folate required to normalize plasma homocysteine levels in patients with sickle cell disease may be higher than that of normal controls and that patients with sickle cell disease have a higher nutritional requirement for folic acid than the general population.

Reactive species in sickle cell disease.

The red cell is a relatively abundant locus of both free radical generation and reaction. Erythrocytes have a high content of unsaturated membrane lipids, a rich oxygen supply and are densely packed with redox-active hemoglobin residues. In response, red cells have a highly evolved and well-integrated network of oxidant defense mechanisms that lend an ability to withstand oxidative stress. In the case of congenital hemoglobin mutations that underlie sickle cell disease, they become very susceptible to free radical-mediated injury by virtue of enhanced endogenous rates of production of reactive species and impairment of tissue free radical defense mechanisms. In sickle cell disease, a combination of these susceptibility factors are hypothesized to lead to an overall impairment of vascular function, in large part due to loss of "bioactive" nitric oxide via the free radical-mediated consumption of this vasoactive molecule.

A case study of a recent decline in the dialysis fatality rate.

Geoffrey Berlyne, whom we honor in this Festschrift, has contributed much to the modern understanding of diseases of the kidney, and of the clinical and metabolic disorders that occur in acute and chronic renal failure. The Festschrift highlights the many areas of his contributions. It is important to note that underlying them all is astute clinical observation, incisive analysis and reasoning, a breadth of approach, experimentation that facilitated understanding of the relevant clinical issues, and an unusual clarity of exposition in the literature. As author, editor, and teacher, Geoffrey Berlyne has brought this clarity of approach to a generation in nephrology. The following analysis of clinical data from a working dialysis unit, rendering care to a predominantly underprivileged patient population, is presented in the hope that it throws light on everyday problems in nephrology in a manner similar to that in which Geoffrey has guided the nephrology community.

Acetazolamide inhibition of renal gamma-glutamyl transpeptidase.

The effect of acetazolamide (AZ) on renal gamma-glutamyl transpeptidase (EC 2.3.2.2) activity (gamma-GT) was studied with the purified enzyme, subcellular fractions, and in the isolated functioning kidney. Activity of gamma-GT was assessed using either one of two gamma-glutamyl donors, gamma-glutamyl-p-nitroanilide (gamma GpNA) or glutamine, and either the gamma-glutamyl acceptor glycylglycine (Gly-Gly) or methionine (Met). With the microsomal enzyme and beta-GpNA, AZ was shown to inhibit p-nitroaniline (p-NA) formation; however, gamma-GpNA Km remained unchanged (1.8 mM), while the Vmax was reduced significantly, 333 vs 200 mumoles . min-1 . mg-1. Adding Gly-Gly removed AZ inhibition, while AZ elevated the apparent Km from Gly-Gly from 16 to 48; AZ inhibition of gamma-GT activity resulted in a decrease in gamma-glutamyl-Gly-Gly formation consistent with interaction at the gamma-glutamyl acceptor site. With glutamine as the beta-glutamyl donor, AZ reduced NH3 and apparent gamma-glutamylmethionine formation in the purified enzyme in agreement with inhibition at the acceptor site. In the functioning kidney, perfused with 10(-3)M L- or D-glutamine, AZ (10(-3)M) markedly reduced NH3 formation and increased glutamine excretion, results consistent with AZ inhibition of the in situ gamma-GT.