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Mitochondrial disorders are genetic defects of oxidative phosphorylation. Oxidative phosphorylation takes place in the mitochondrial inner membrane and consists of the oxidation of fuel molecules by oxygen and the concomitant energy transduction into ATP. The mitochondrial respiratory chain is a complex metabolic pathway. It is made of approximately 100 polypeptides, most of which are encoded in the nucleus whereas 13 are encoded in the mitochondria. Mitochondrial DNA is maternally inherited and its mutations are transmitted by the mother. During cell division, mitochondria are randomly partitioned in daughter cells. Therefore, in case normal and mutant DNA are present in the mother's cells, some lineage may have only mutant mitochondrial DNA or normal mitochondrial DNA while others may have both mutant and normal DNA, a condition named heteroplasmy. Renal involvement in mitochondrial cytopathies is rare. Patients most often present with a more or less complete de Toni-Debré-Fanconi syndrome. A few patients present with a nephrotic syndrome or with chronic tubulointerstitial nephritis. The investigation of patients with mitochondrial disorders include metabolic screening for abnormal oxidoreduction status in plasma, investigation of the mitochondrial respiratory chain, including polarographic and spectrophotometric studies, histopathologic studies and genetic studies.

Immunosuppressive treatment following renal transplantation includes induction therapy during the initial period when the risk of rejection is higher. Depleting anti-lymphocyte antibodies are indicated mostly in patients who developped anti-HLA antibodies and following a second graft. Anti-IL2 receptor antibodies may be used in non-responders. After the first month, maintenance therapy mostly consists in the association of several immunosuppressants, mainly corticosteroids, an antimetabolic agent (azathioprine or mycophenolate mofetil) and a calcineurin inhibitor (cyclosporine or tacrolimus). Side effects associated with these treatments led to the development of new immunosuppressive protocols, with the reduction or withdrawal of corticosteroids treatment due to its deleterious effects on statural growth, and decreased doses of anti-calcineurin agents to reduce their nephrotoxic effect. These therapeutic options are possible in patients at low immunological risk.

The European patents for epoetin alpha recently expired. Biosimilars (i.e. "a medicine which is similar to a biological medicine that has already been authorized" [EMEA 2007]) of epoetins have thus been released on the market in Europe. Because of the complexity of the processes that are required to produce medicinal products containing biotechnology-derived proteins as active substances and to characterize the physicochemical properties of these compounds, the guidelines that have been developed for generic drugs cannot be used for approval of biosimilar products. The EMEA guidelines do not answer all questions that have been raised for the development of biosimilars, and in some cases, decisions will have to be taken at a national level. This is why the Society of Nephrology (Société de néphrologie), the French-speaking Society of Dialysis (Société francophone de dialyse) and the Pediatric Society of Nephrology (Société de néphrologie pédiatrique) established guidelines for the usage of biosimilar epoetins concerning approval, identification, substitution of an innovator drug, post-marketing surveillance, extension of indication and pharmacovigilance plan.

Hemolytic and uremic syndrome (HUS) is characterized by the association of hemolytic anemia with sckizocytes, thrombopenia and renal involvement secondary to thrombotic microangiopathy. The typical form is the most frequent in children occurring after an episode of diarrhea caused by Escherichia coli. Other microorganisms may be responsible for HUS such as Shigella dysenteriae or streptococcus pneumoniae. Acute renal failure is reversible in most cases, but long-term renal sequelae are seen in one third of patients when the anuria at onset of disease has lasted more than one week. Treatment of typical HUS is only supportive (blood transfusion, treatment of acute renal failure). Atypical HUS is less frequent but of poorer prognosis. Atypical HUS may be associated with mutations in complement regulator genes, von Willebrand factor-cleaving protease deficiency, congenital intracellular defects of vitamin B12 metabolism or may be of unknown origin. Familial forms are frequent. Recurrence of HUS following renal transplantation is exceptional in the typical form but is frequent in atypical HUS.

Nephronophthisis is a chronic tubulo-interstitial nephritis which progress to terminal renal failure. It is an heterogeneous entity at the clinical as well as at the genetic level. There are three main clinical forms of nephronophtisis which have been associated with five gene defects. Juvenile nephronophtisis, the most frequent, progress to end stage renal failure before age 15. It is an autosomal recessive disease which is responsible for a urine concentration defect starting after age 2, failure to thrive and a progressive deterioration of renal function without signs of glomerular disease. Kidney size is normal. Histologic lesions concern tubular basement membranes which are thickened and multilayered or thinned. There is an associated interstitial fibrosis. Some children present with extrarenal symptoms: tapetoretinal degeneration (Senior-Loken syndrome), mental retardation, cerebellar ataxia, bone anomalies or liver involvement. Infantile nephronophtisis is a recessive autosomic tubulo-interstitial nephritis with cortical microcysts which progress to end stage renal failure before age 5. Adolescent nephronophtisis is a less frequent form of nephronophtisis. Medullary cystic disease is transmitted as an autosomic dominant trait. Clinical and histological signs are similar to nephronophthisis, but the disease progress later to terminal renal failure and is not accompanied by extra-renal symptoms. Several genes which are involved in nephronophtisis, encode proteins that localize in different cell compartments, in particular to the primary apical cilia, as it is the case for many other cystic kidney diseases.

Congenital nephrotic syndrome is present at birth or appears during the first three months of life and infantile nephrotic syndrome during the first year. Finnish type congenital nephrotic syndrome is an autosomal recessive disease. Nephrotic syndrome is present at birth, severe and does not respond to therapy. Infectious and nutritional complications are frequent. Renal function deteriorates necessitating a dialysis-transplantation program. Between age five and eight. The disease does not recur after transplantation. Diffuse mesangial sclerosis is the second cause of congenital and infantile nephrotic syndrome. It may be isolated or part of a Denys-Drash syndrome (association of the nephropathy with male pseudohermaphroditism and Wilm's tumor). Nephrotic syndrome is resistant to therapy. Renal failure develops in early childhood. Therapy is aimed to prevent oedema, denutrition, infections and thrombosis. Proteinuria does not recur after renal transplantation. Other causes are less frequent.