Characterization and review of MTHFD1 deficiency: four new patients, cellular delineation and response to folic and folinic acid treatment.

In the folate cycle MTHFD1, encoded by MTHFD1, is a trifunctional enzyme containing 5,10-methylenetetrahydrofolate dehydrogenase, 5,10-methenyltetrahydrofolate cyclohydrolase and 10-formyltetrahydrofolate synthetase activity. To date, only one patient with MTHFD1 deficiency, presenting with hyperhomocysteinemia, megaloblastic anaemia, hemolytic uremic syndrome (HUS) and severe combined immunodeficiency, has been identified (Watkins et al J Med Genet 48:590-2, 2011). We now describe four additional patients from two different families. The second patient presented with hyperhomocysteinemia, megaloblastic anaemia, HUS, microangiopathy and retinopathy; all except the retinopathy resolved after treatment with hydroxocobalamin, betaine and folinic acid. The third patient developed megaloblastic anaemia, infection, autoimmune disease and moderate liver fibrosis but not hyperhomocysteinemia, and was successfully treated with a regime that included and was eventually reduced to folic acid. The other two, elder siblings of the third patient, died at 9 weeks of age with megaloblastic anaemia, infection and severe acidosis and had MTFHD1 deficiency diagnosed retrospectively. We identified a missense mutation (c.806C > T, p.Thr296Ile) and a splice site mutation (c.1674G > A) leading to exon skipping in the second patient, while the other three harboured a missense mutation (c.146C > T, p.Ser49Phe) and a premature stop mutation (c.673G > T, p.Glu225*), all of which were novel. Patient fibroblast studies revealed severely reduced methionine formation from [(14)C]-formate, which did not increase in cobalamin supplemented culture medium but was responsive to folic and folinic acid. These additional cases increase the clinical spectrum of this intriguing defect, provide in vitro evidence of disturbed methionine synthesis and substantiate the effectiveness of folic or folinic acid treatment.

Failure of bortezomib to cure acute antibody-mediated rejection in a non-compliant renal transplant patient.

Bortezomib has appeared recently as a potential active treatment for acute AMR for few years. We reported a patient who received two courses of bortezomib for the treatment of an acute AMR associated with de novo HLA DSA that occurred 18 months after renal transplantation because of non-compliance. Graft biopsy revealed features of acute humoral rejection with plasmocyte infiltration and C4d staining. Bortezomib was associated with corticosteroid pulses, IVIgs, and PP. Despite this rapid management, the patient lost his graft and carried on dialysis. Bortezomib therapy in addition to current therapy of AMR is not always effective in the treatment for late acute AMR in renal transplantation. We discuss on the place of such a treatment and other therapeutic strategies in this indication.

The natural history of clinical operational tolerance after kidney transplantation through twenty-seven cases.

We report here on a European cohort of 27 kidney transplant recipients displaying operational tolerance, compared to two cohorts of matched kidney transplant recipients under immunosuppression and patients who stopped immunosuppressive drugs and presented with rejection. We report that a lower proportion of operationally tolerant patients received induction therapy (52% without induction therapy vs. 78.3%[p = 0.0455] and 96.7%[p = 0.0001], respectively), a difference likely due to the higher proportion (18.5%) of HLA matched recipients in the tolerant cohort. These patients were also significantly older at the time of transplantation (p = 0.0211) and immunosuppression withdrawal (p = 0.0002) than recipients who rejected their graft after weaning. Finally, these patients were at lower risk of infectious disease. Among the 27 patients defined as operationally tolerant at the time of inclusion, 19 still display stable graft function (mean 9 ± 4 years after transplantation) whereas 30% presented slow deterioration of graft function. Six of these patients tested positive for pre-graft anti-HLA antibodies. Biopsy histology studies revealed an active immunologically driven mechanism for half of them, associated with DSA in the absence of C4d. This study suggests that operational tolerance can persist as a robust phenomenon, although eventual graft loss does occur in some patients, particularly in the setting of donor-specific alloantibody.

[Value of multidetector-row computed tomography for infantile renovascular hypertension: report of two cases]. / Apport de la tomodensitométrie multicoupe dans l'hypertension rénovasculaire du nourrisson: à propos de deux cas.

The work-up of renovascular hypertension (10% of children hypertension cases) benefits from multiple imaging modalities. These two cases show the difficulties encountered with infant and underscore "the major role" of the computed tomography angiography within for diagnosis and management. Indeed CTA allows reproducible studies of abdominal vessels at the expense of radiation exposure.

CYP24A1 Mutations in a Cohort of Hypercalcemic Patients: Evidence for a Recessive Trait.

CONTEXT: Loss-of-function mutations of CYP24A1 (which encodes the 25-OH-D3-24-hydroxylase) have recently been reported to cause hypercalcemia. OBJECTIVES: The aims of this study were: 1) to evaluate the frequency of CYP24A1 mutations in patients with medical history of hypercalcemia; 2) to show the clinical utility of a simultaneous assay of serum 25-hydroxyvitamin D3 (25-OH-D3) and 24,25-dihydroxyvitamin D3 (24,25-[OH]2D3) by liquid chromatography tandem mass spectrometry (LC-MS/MS); and 3) to investigate biochemical parameters in heterozygous gene carriers with CYP24A1 mutations. PATIENTS AND METHODS: We screened for CYP24A1 mutations in 72 patients with serum calcium levels > 2.6 mmol/L and PTH levels < 20 pg/mL and recruited 24 relatives after genetic counseling for subsequent investigations. Vitamin D metabolite concentrations were assessed in a subset of patients by LC-MS/MS and results expressed as a ratio (R) of 25-OH-D3:24,25-(OH)2D3. RESULTS: Twenty-five patients with hypercalcemia (35%) harbored CYP24A1 variations. Twenty (28%) had biallelic variations, mostly found in subjects with nephrocalcinosis or renal stones (19/20). Five patients, all neonates, were heterozygous, without renal disease. We describe 15 new variations leading to loss-of-function according to pathogenicity prediction programs, and we functionally characterized 5 of them in vitro. A dramatic increase of R, usually >80, was found in patients harboring biallelic mutations providing evidence in vivo for the loss of CYP24A1 activity. In contrast, R value remains <25 in patients without CYP24A1 mutations. Subjects carrying one mutant allele, hypercalcemic individuals, as well as gene-carrier relatives, had a detectable 24,25-(OH)2D3 level and R < 25, indicating normal 24-hydroxylase activity. CONCLUSION: CYP24A1 biallelic mutations are frequently found in patients presenting with hypercalcemia, low PTH, and renal disease. We confirm the accuracy and effectiveness of a novel blood test estimating the ratio between relevant vitamin D metabolites as a useful screening tool for CYP24A1 mutations. Haploinsufficiency is not associated with CYP24A1 deficiency.

Population pharmacokinetics and pharmacogenetics of tacrolimus in de novo pediatric kidney transplant recipients.

The aim of this study was to develop a population pharmacokinetic model of tacrolimus in pediatric kidney transplant patients, identify factors that explain variability, and determine dosage regimens. Pharmacokinetic samples were collected from 50 de novo pediatric kidney transplant patients (age 2-18 years) who were on tacrolimus treatment. Population pharmacokinetic analysis of tacrolimus was performed using NONMEM, and the impact of variables (demographic and clinical factors, and CYP3A4-A5, ABCB1, and ABCC2 polymorphisms) was tested. The pharmacokinetic data were described by a two-compartment model that incorporated first-order absorption and lag time. The apparent oral clearance (CL/F) was significantly related to body weight (allometric scaling); in addition, it was higher in patients with low hematocrit levels and lower in patients with CYP3A5*3/*3. The population pharmacokinetic-pharmacogenetic model developed in de novo pediatric kidney transplant patients demonstrated that, in children, tacrolimus dosage should be based on weight, hematocrit levels, and CYP3A5 polymorphism. Individualization of therapy will enable the optimization of tacrolimus exposure, with resultant beneficial effects on kidney function in the initial post-transplantation period.