Sudden Cardiac Death Due to Deficiency of the Mitochondrial Inorganic Pyrophosphatase PPA2.

We have used whole-exome sequencing in ten individuals from four unrelated pedigrees to identify biallelic missense mutations in the nuclear-encoded mitochondrial inorganic pyrophosphatase (PPA2) that are associated with mitochondrial disease. These individuals show a range of severity, indicating that PPA2 mutations may cause a spectrum of mitochondrial disease phenotypes. Severe symptoms include seizures, lactic acidosis, cardiac arrhythmia, and death within days of birth. In the index family, presentation was milder and manifested as cardiac fibrosis and an exquisite sensitivity to alcohol, leading to sudden arrhythmic cardiac death in the second decade of life. Comparison of normal and mutant PPA2-containing mitochondria from fibroblasts showed that the activity of inorganic pyrophosphatase was significantly reduced in affected individuals. Recombinant PPA2 enzymes modeling hypomorphic missense mutations had decreased activity that correlated with disease severity. These findings confirm the pathogenicity of PPA2 mutations and suggest that PPA2 is a cardiomyopathy-associated protein, which has a greater physiological importance in mitochondrial function than previously recognized.

Investigating the effects of endogenous lipaemia on the measurement of sodium by indirect ion specific electrode potentiometry.

BACKGROUND: The widely automated method using indirect ion specific electrodes (ISE) potentiometry for determination of sodium concentration is prone to interference from lipaemia. Manufacturer-specified lipaemic (L)-index cut offs may underestimate the effects of endogenous lipaemia. METHODS: We assessed the interference on sodium concentration caused by endogenous lipaemia in 32 residual samples (from 13 patients) using indirect ISE (Cobas® 8000 modular analyser with c702 module, Roche diagnostics) and direct ISE (GEM 4000 premier, Werfen) potentiometric methods. Regression analysis (linear and non-linear) was used to determine a reliable (L)-index cut off for reporting sodium concentration. RESULTS: There was a poor correlation observed between triglyceride concentration and (L)-index. There was significant negative interference caused by endogenous lipaemia within analysed samples. Non-linear regression demonstrated a negative interference of approximately 5% at an (L)-index of 250. CONCLUSION: At present, the manufacturer advises not to report sodium concentration by indirect ISE on the Cobas® 8000 modular analyser if the (L)-index is >2000. However, this has been determined by the addition of exogenous lipids (Intralipid®) and it is clear that this is not comparable to endogenous lipaemia. To ensure patient safety, clinical laboratories should consider lowering the cut off for (L)-index that they use for reporting sodium concentration.

Three-Country Snapshot of Ornithine Transcarbamylase Deficiency.

X-linked ornithine transcarbamylase deficiency (OTCD) is the most common urea cycle defect. The disease severity ranges from asymptomatic carrier state to severe neonatal presentation with hyperammonaemic encephalopathy. We audited the diagnosis and management of OTCD, using an online 12-question-survey that was sent to 75 metabolic centres in Turkey, France and the UK. Thirty-nine centres responded and 495 patients were reported in total. A total of 208 French patients were reported, including 71 (34%) males, 86 (41%) symptomatic and 51 (25%) asymptomatic females. Eighty-five Turkish patients included 32 (38%) males, 39 (46%) symptomatic and 14 (16%) asymptomatic females. Out of the 202 UK patients, 66 (33%) were male, 83 (41%) asymptomatic and 53 (26%) symptomatic females. A total of 19%, 12% and 7% of the patients presented with a neonatal-onset phenotype in France, Turkey and the UK, respectively. Vomiting, altered mental status and encephalopathy were the most common initial symptoms in all three countries. While 69% in France and 79% in Turkey were receiving protein restriction, 42% were on a protein-restricted diet in the UK. A total of 76%, 47% and 33% of patients were treated with ammonia scavengers in Turkey, France and the UK, respectively. The findings of our audit emphasize the differences and similarities in manifestations and management practices in three countries.

Elevated soluble cellular adhesion molecules are associated with increased mortality in a prospective cohort of renal transplant recipients.

BACKGROUND: Increased plasma levels of cellular adhesion molecules (CAMs) have been shown to be predictors of all cause mortality in individuals with chronic renal failure 12 and patients with end-stage renal disease receiving haemodialysis 3. In renal transplant recipients the predictive value of CAMs has not been well characterised. The aim of this study was to assess the relationship between CAMs and all-cause mortality during prospective follow-up of a renal transplant cohort. METHODS: A total of 378 renal transplant recipients were recruited between June 2000 and December 2002. Soluble vascular CAM-1 (VCAM) and soluble intercellular CAM-1 (ICAM) were measured at baseline and prospective follow-up data was collected at a median of 2441 days after enrolment. RESULTS: In univariate survival analysis the renal transplant recipients with a VCAM or ICAM concentration in the lowest third were significantly more likely to have survived at follow-up (p < 0.001 and p = 0.009 respectively). In multivariate survival analysis VCAM and ICAM remained significant independent predictors of mortality following adjustment for traditional cardiovascular risk factors, hsCRP and estimated GFR (p = 0.030 and p = 0.037 respectively). CONCLUSIONS: The results of this prospective study are the first to show that the CAMs, ICAM and particularly VCAM, are significant independent predictors of mortality in patients with a renal transplant.

Elevated homocysteine is a predictor of all-cause mortality in a prospective cohort of renal transplant recipients.

BACKGROUND: In patients with chronic kidney disease, an elevated homocysteine concentration is associated with an increased incidence of cardiovascular events. AIM: The aim of this study was to investigate the relationship between homocysteine concentration and all-cause mortality during prospective follow-up of a renal transplant cohort. METHODS: A total of 378 renal transplant recipients were recruited between June 2000 and December 2002. Homocysteine was measured at baseline and mortality data was collected at a median of 2,441 days after enrolment. RESULTS: In univariate analysis, homocysteine was a significant predictor of mortality (p < 0.001). In multivariate analysis, homocysteine remained a significant independent predictor of mortality following adjustment for traditional cardiovascular risk factors (p = 0.01), vitamin B(12) and folate (p < 0.001) and estimated glomerular filtration rate (p = 0.03). CONCLUSIONS: In the renal transplant recipients enrolled in this study, homocysteine concentration was a significant predictor of mortality in univariate survival analysis and in multivariate survival analysis following adjustment for traditional cardiovascular risk factors and following adjustment for renal function. Assessing the effect of lowering homocysteine concentration on the survival of patients with a renal transplant is therefore worthy of further study.

Troponin T is an independent predictor of mortality in renal transplant recipients.

BACKGROUND: Numerous reports have demonstrated an association between elevated Troponin T levels and adverse cardiovascular outcomes in patients with chronic kidney disease. However, whether raised Troponin T levels are an independent predictor of mortality in renal transplant recipients has not yet been established. The aim of this study was, therefore, to assess the use of Troponin T as a prognostic marker in a population of renal transplant recipients. METHODS: Three hundred and seventy-two asymptomatic renal transplant recipients were recruited between June 2000 and December 2002. Troponin T was measured at baseline and prospective follow-up data were collected at a median of 1739 days. RESULTS: In Kaplan-Meier analysis a Troponin T level > or = 0.03 microg/l was a significant predictor of mortality (P < 0.001). In Cox Regression analysis, an elevated Troponin T level remained a significant predictor of mortality following adjustment for traditional cardiovascular risk factors (P < 0.001) and following adjustment for estimated glomerular filtration rate and high sensitivity C reactive protein (P < 0.001). CONCLUSIONS: Elevated Troponin T level is a strong independent predictor of all cause mortality in patients with a renal transplant. Troponin T, therefore, represents a promising biochemical marker that identifies those renal transplant recipients who are most likely to benefit from aggressive cardiovascular risk factor modification.

Elevated serum phosphate predicts mortality in renal transplant recipients.

BACKGROUND: High serum phosphate has been identified as an important contributor to the vascular calcification seen in patients with chronic kidney disease (Block et al., Am J Kidney Dis 1998; 31: 607). In patients on hemodialysis, elevated serum phosphate levels are an independent predictor of mortality (Block et al., Am J Kidney Dis 1998; 31: 607; Block, Curr Opin Nephrol Hypertens 2001; 10: 741). The aim of this study was to investigate whether an elevated serum phosphate level was an independent predictor of mortality in patients with a renal transplant. METHODS: Three hundred seventy-nine asymptomatic renal transplant recipients were recruited between June 2000 and December 2002. Serum phosphate was measured at baseline and prospective follow-up data were collected at a median of 2441 days after enrolment. RESULTS: Serum phosphate was significantly higher in those renal transplant recipients who died at follow-up when compared with those who were still alive at follow-up (P<0.001). In Kaplan-Meier analysis, serum phosphate concentration was a significant predictor of mortality (P=0.0001). In multivariate Cox regression analysis, serum phosphate concentration remained a statistically significant predictor of all-cause mortality after adjustment for traditional cardiovascular risk factors, estimated glomerular filtration rate, and high sensitivity C reactive protein (P=0.036) and after adjustment for renal graft failure (P=0.001). CONCLUSIONS: The results of this prospective study are the first to show that a higher serum phosphate is a predictor of mortality in patients with a renal transplant and suggest that serum phosphate provides additional, independent, prognostic information to that provided by traditional risk factors in the risk assessment of patients with a renal transplant.

Decreased serum retinol is associated with increased mortality in renal transplant recipients.

BACKGROUND: Vitamin A plays a central role in epithelial integrity and immune function. Given the risk of infection after transplantation, adequate vitamin A concentrations may be important in patients with a transplant. We assessed whether there was an association between retinol concentration and all-cause mortality in renal transplant recipients. METHODS: We recruited 379 asymptomatic renal transplant recipients between June 2000 and December 2002. We measured serum retinol at baseline and collected prospective follow-up data at a median of 1739 days. RESULTS: Retinol was significantly decreased in those renal transplant recipients who had died at follow-up compared with those who were still alive at follow-up. Kaplan-Meier analysis showed that retinol concentration was a significant predictor of mortality. In multivariate Cox regression analysis, decreased retinol concentration remained a statistically significant predictor of all-cause mortality after adjustment for traditional cardiovascular risk factors, high-sensitivity C-reactive protein, and estimated glomerular filtration rate. CONCLUSIONS: Serum retinol concentration is a significant independent predictor of all-cause mortality in renal transplantation patients. Higher retinol concentration might impart a survival advantage via an antiinflammatory or anti-infective mechanism.