Background: The Robertsonian translocations inherited from parents with a normal phenotype are often discovered through children with pathogenesis. The exact causes of pathologies in children with clinical manifestations are often unknown and vary greatly in the reported cases: uniparental disomy, de novo rearrangements, changes in methylation patterns and gene expression, including ribosomal genes. Aim of the study: Molecular-cytogenetic investigation of a clinical case of intellectual disability. Material and methods: GTG-banding, Ag-NOR staining, fluorescent in situ hybridization, PCR, real-time PCR. Results: We describe a family case of a translocation rob (13; 14) and elevated rRNA expression in the proband with developmental delay and in his phenotypically normal mother. We show the loss of the p-arms of original chromosomes and the absence of NORs on the derived chromosome. The whole-chromosome uniparental disomy is excluded. Conclusion: The translocated chromosome in the proband was most likely inherited from the mother and did not come about de novo with normal chromosomes 13 and 14 being obtained from the father. The cause of the pathogenesis in the proband still remains unknown. We hypothesize that it could be caused by impaired imprinting manifesting in altered methylation levels of loci on the derivative chromosome.