Respiratory chain deficiency presenting as congenital nephrotic syndrome

Nephrotic syndrome (NS) in infancy includes NS of Finnish type (mutation of the nephrin gene), diffuse mesangial sclerosis (idiopathic or linked to WT1 mutation), idiopathic NS, most often steroid resistant, and NS related to infections during pregnancy (virus, syphilis, toxoplasmosis). Later in life, NS has a large variety of etiologies. It has been described in association with neuromuscular symptoms, deafness, and diabetes in a few children and adults with respiratory chain (RC) disorders. To date, however, NS has never been observed in neonates with RC disorders. Here, we report RC deficiency in one infant with certain congenital NS and two siblings with acute neonatal cardiac and renal disease with probable NS. Although clinical and histopathological presentations were initially close to congenital NS of Finnish type, clinical outcome was atypical and nephrin mutation was excluded. Mitochondrial RC complex II+V deficiency was identified in the three patients. Based on these observations, we suggest that RC disorders should be considered in patients with congenital NS.