#6786 ADTKD DUE TO MUC-1 GENE MUTATION: A MAJOR DIAGNOSTIC CHALLENGE, NOT IDENTIFIED BY EXOME SEQUENCING

Abstract

Abstract Background and Aims Autosomal dominant tubulointerstitial renal disease (ADTKD) is a rare cause of end-stage renal disease (ESKD) in adulthood. In addition to its rarity, ADTKD is probably underdiagnosed due to the very non-specific and heterogeneous clinical-laboratory-histopathological-instrumental picture and because of the diagnostic need to use specific methods of genetic investigation in order to highlight the mutations within the VNTR sequences of the MUC1 gene, not recognized by the most common exome sequencing. Mutations in the MUC1 gene, together with those in the UMOD gene, are the main mutations implicated in the pathogenesis of ADTKD. Method We analyzed the clinical, laboratory and histopathological characteristics of four families followed by our center with suspected diagnosis of ADTKD and detection of mutation of the MUC1 gene. Results Our data (Table 1) revealed a marked phenotypic variability, even within members of the same family (Fig. 1), and in particular as regards the age of disease onset and the different rate of progression towards ESKD (range 16 – 88 years). From a laboratory point of view, in 10 out of 13 patients the sediment was negative, and only in 3 patients proteinuria >1 g/24h was highlighted. In 6/13 the onset occurred at the age of less than 35 years and among these, 4 of them presented ESKD early. In the few cases in which renal biopsy was performed (4/17), representing 0.4% of all biopsies in our centre, the most frequent finding was the presence of tubular atrophy and interstitial fibrosis (3/4), with cystic ectasia of the tubular lumen at the cortical-medullary level in half of the cases. Among the 10 patients subjected to genetic analysis, only in one case the mutation was highlighted by exome sequencing. Conclusion The large phenotypic variability, in particular of age at achievement of ESKD, suggests that other factors (modifier or environmental genes) could also affect disease progression. Common gene sequencing methods (e.g. exome sequencing, Sanger) have proved unable, in most cases, to identify mutations within the VNTR sequences of the MUC1 gene.