This Month in AJKD

Article Outline

• Oxalate Transport and its Role in Hyperoxaluria
• Association of Race With EPO Dose
• De Novo Mutations in Autosomal Dominant PKD
• Temporal Trends in Red Blood Transfusion

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Oxalate Transport and its Role in Hyperoxaluria 

See Monico et al, pages 1096-1103; and Rumsby, pages 1031-1034.

Hyperoxaluria is a major risk factor for calcium oxalate stones, and can lead to significant morbidity and mortality. Primary hyperoxaluria (PH) types 1 and 2 (PH1 and PH2, respectively) are caused by mutations causing increased oxalate production. In this issue, Monico et al explore the hypothesis that hyperoxaluria may also be caused by defects in oxalate transport, specifically in the chloride/oxalate exchanger SLC26A6. They performed a cross-sectional case-control study of patients with PH1, PH2, and atypical PH not associated with PH1 or PH2. A rare sequence variant of SLC26A6, c.487C→T (p.Pro163Ser), was detected solely in 1 pedigree, but this variant failed to segregate with hyperoxaluria, and functional studies of oxalate transport in Xenopus oocytes showed no defect. No other variant was identified specifically in non-PH1/PH2. Although the results from this study were inconclusive, an accompanying editorial by Rumsby notes that it is still possible that SLC26A6 mutations may play a role in oxalate transport.

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Association of Race With EPO Dose 

See Lacson et al, pages 1104-1114; and Kaufman, pages 1035-1038.

Medicare claims data indicate that African American patients on hemodialysis receive greater doses of erythropoietin (EPO) than white patients when achieving similar hemoglobin levels. In this issue, Lacson et al studied 44,721 primary Medicare-insured white (57%) and African American (43%) long-term hemodialysis patients treated by Fresenius Medical Care who received EPO from January 1 to 31, 2004. After adjustment for baseline demographic and laboratory variables, they found that African American patients received 12.6% more EPO than white patients (95% confidence interval, 10.9% to 14.3% [P = 0.001]). The increased EPO dose persisted after adjustment for hemoglobin values in the prior 3 months. There was also a disproportionately higher prevalence of African American patients at higher quintiles of EPO dose. An editorial by AJKD's new co-editor, James Kaufman, offers an interpretation of Lacson et al's findings and interpretations.

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De Novo Mutations in Autosomal Dominant PKD 

See Reed et al, pages 1042-1050.

A small percentage of patients with autosomal dominant polycystic kidney disease (ADPKD) have no apparent family history. There are several possible explanations for this, including occurrence of a de novo pathogenic sequence variant or extreme phenotypic variability. In order to examine these possible explanations, Reed et al present a case series of 24 patients with ADPKD phenotype, no family history of PKD, and both parents living, in which the patients and their parents were screened for the presence or absence of PKD1 or PKD2 pathogenic sequence variants. Six patients were found with documented parentage in which the ADPKD sequence variant was not found in either biological parent. A positive diagnosis of ADPKD by ultrasound or genetic screening was made in a parent for 4 of the patients (17%). No PKD1 or PKD2 pathogenic sequence variants were identified in 10 patients (42%) while possible pathological DNA variants were identified in 4 patients (17%) and 1 of their respective parents. The authors conclude that denovo pathogenic sequence variants may explain some cases of ADPKD in patients with no family history.

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Temporal Trends in Red Blood Transfusion 

See Ibrahim et al, pages 1115-1121.

Although it is commonly held that the use of erythropoiesis-stimulating agents in dialysis patients has decreased the need for red blood cell transfusions, quantitative data are quite limited. Thus, in this issue Ibrahim et al analyzed transfusion rates in point prevalent dialysis patients from 1992 to 2005, using US Renal Data System data. The preceding 6 months were used to assemble a comorbidity profile based on administrative claims data. The first cohort consisted of 77,347 patients on January 1, 1992, and the last cohort consisted of 164,933 patients on January 1, 2005. Each annual cohort was followed up for transfusion events for 1 year. The authors found that unadjusted transfusion rates decreased in both outpatient and inpatient settings from 535.33/1,000 patient-years for 1992 prevalent dialysis patients to 263.65/1,000 patient-years in 2005 (P for trend = 0.001, 1992 versus 1999 and 1999 versus 2005). Adjusted rates decreased similarly. This phenomenon could not be explained by changes in case mix.

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