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Background: Mitochondrial tRNA (MTT) genes are hotspot for mitochondrial DNA mutation and are responsible of half mitochondrial disease. MTT mutations are associated with a broad spectrum of phenotype often with complex multisystem involvement and complex genotype-phenotype correlations. MT-TL1 mutations, among which the m.3243A>G mutation is the most frequent, are associated with myopathy, maternal inherited diabetes and deafness, MELAS, cardiomyopathy, and focal segmental glomerulosclerosis. Case study: Here we report the case of an Italian 49-years old female presenting with encephalomyopathy, chronic proteinuric kidney disease and a new heteroplasmic m.3274_3275delAC MT-TL1 gene mutation. Conclusions: Our case demonstrates a systemic mitochondrial disease caused by the heteroplasmic m.3274_3275delAC MT-TL1 gene mutation, not yet described in the literature. A mitochondrial disease should be suspected in case of complex multisystem phenotypes, including steroid-resistant nephrotic syndrome with multisystemic involvement.

The percutaneous biopsy of native kidneys according to the classic methodology, takes place with the introduction of the needle and its guide with ultrasound sagittal viewing planes, with a 30-degree angle, up to the lower pole of the kidney. Since the longitudinal axis of the kidneys converges towards the spine with a sharp angle, we observed that starting from a longitudinal scan of the kidney (conducted along the posterior axillary line with the patient prone) you can drive the needle by a perforated probe through a shorter path perpendicular to the end section of the lower pole of the kidney where the front and rear rims of the cortex bearings without the renal sinus interposed so increasing the chance to obtain, even with a single pass, a good sample of cortical tissue while limiting the possibility to damage the lower chalices that may cause hematuria. We biopsied in that manner 26 patients and we compared the data with those reported in the literature performed with the same needle gauge and post-biopsy monitoring period. With a statistically lower number of needle passes, it is thus obtained the 100% of the sample validity for histological analysis, in absence of major complications and statistically hemoglobin variance when compared with a group of 44 patients biopsied with a significantly greater number of needle passes in the only work carried out with classical technique in the literature (Ori et al.) which is directly comparable to our for gauge of the needles and duration of monitoring.