Toward personalized medicine in renal transplantation.

BACKGROUND: The pharmacokinetics of tacrolimus (TRL) are clearly affected by genetic polymorphisms in drug-metabolizing enzymes, which lead to large interindividual differences in dose-response relations. In addition, TRL has a narrow therapeutic index requiring monitoring of blood levels. The objective of the present observational, retrospective study was to associate maintenance TRL doses with various genetic markers seeking to guide optimization of the initial dose. METHODS: Results of DNA samples from 15 kidney transplant patients were correlated retrospectively with clinical information from medical records. Samples were genotyped using PHARMAchip. Association studies were performed with χ2 and Pearson tests and by analysis of variance. The study was carried out in accordance with international ethical standards of the Helsinki Declaration and approved by our ethics committee. RESULTS: Two patient groups were identified to show a difference in TRL dose requirements: a control (0.014-0.10 mg/kg/per day) and an high-dose group (0.14-0.15 mg/kg/per day). The presence of CYP3A5*1 and the null allele in GSTM1 were significantly associated (P=.01 and P=.04) with the need for higher immunosuppressive doses (>0.10 mg/kg/per day). There were no differences in plasma levels of TRL or other clinical variables between the patient groups. CONCLUSION: Determination of the CYP3A5 genotype might be used to predict initial TRL requirements, although other genetic variants also provide important information to adjust the drug dose.

Familial hypokalemia-hypomagnesemia or Gitelman's syndrome: a further case.

A woman aged 33 years presented hypokalemia and hypomagnesemia associated with renal potassium and magnesium wasting. Her mean 24-hour urinary calcium excretion was strikingly low despite normocalcemia, normal creatinine clearance, normal serum PTH and calcitriol. Normal distal fractional chloride reabsorption [CH2O/(CH2O + CCl)] was noted during water load but was reduced during hypotonic saline infusion. In response to intravenous furosemide (1 mg/kg), the patient showed significant increments in sodium, chloride and magnesium excretion as well as abolition of hypocalciuria. The association of renal calcium transport from magnesium transport together with exaggerated natriuresis after furosemide suggests the presence of a defect in the distal tubule rather than in the loop of Henle. We propose that our patient is affected by the syndrome of primary renotubular hypomagnesemia-hypokalemia with hypocalciuria, known as Gitelman's syndrome.