Treatment of rare inherited diseases remains to be a challenging task. The young female patient was diagnosed with chronic recurrent multifocal osteomyelitis in childhood. During an early puberty, a panoramic X-ray of the jaws revealed numerous defects in the anatomy of the teeth, which included significant root shortening. In addition, her blood tests repeatedly showed abnormalities in phosphorus and vitamin D levels. However, no clear association was found to link the diagnoses. To identify the possible causative agent of these diseases, whole-exome sequencing of her DNA was recently performed. The patient was found to be a carrier of an extremely rare allele of the gene for polypeptide N-Acetylgalactosaminyltransferase 3 (GALNT3) as a recessive homozygote. Mutation in this gene was in a few clinical case studies associated with hyperphosphatemic familial tumoral calcinosis and hyperphosphatemic hyperostosis syndrome. Modelling of the protein structure showed that the identified point mutation in this conserved sequence causes conformational changes in the protein with a presumed change in its function. In order to study the identified inherited disease, a genetically modified mouse model carrying the same point mutation was created. Studying this mouse model will not only provide the opportunity to explore all phenotypic manifestations but more importantly, to test new therapies.