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.

Dominant Tolerance to Kidney Allografts Induced by Anti-Donor MHC Class II Antibodies: Cooperation between T and Non-T CD103+Cells

Allograft acceptance can be induced in the rat by pretransplant infusion of donor blood or spleen cells. Although promoting long-term acceptance, this treatment is also associated with chronic rejection. In this study, we show that a single administration of anti-donor MHC class II alloimmune serum on the day of transplantation results in indefinite survival of a MHC-mismatched kidney graft. Long-term recipients accept a donor-type skin graft and display no histological evidence of chronic rejection. The kidney grafts of tolerant animals display an accumulation of TCR Cbeta, FoxP3, and IDO transcripts. Moreover, as compared with syngeneic recipients, tolerant recipients harbor a large infiltrate of MHC class II(+) cells and CD103(+) cells. In vitro, splenocytes from tolerant recipients exhibit decreased donor-specific proliferation, which is restored by depletion of non-T cells and partially restored by the blockade of IDO. Finally, splenocytes from tolerant recipients, but not purified T cell splenocytes, transfer donor-specific infectious tolerance without chronic rejection, after infusion into naive recipients, over two generations. However, splenocytes depleted of T cells or splenocytes depleted of CD103(+) cells fail to transfer tolerance. Collectively, these data show that a single administration of anti-donor MHC class II alloimmune serum induces a tolerant state characterized by an infiltration of the kidney graft by regulatory T cells and CD103(+) cells. These data also show that the transfer of tolerance requires the presence of both T cells and CD103(+) dendritic cells. The precise mechanism of cooperation of these two cell subsets remains to be defined.

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.