The differential diagnosis of young-onset progressive dementia is an issue that requires effort. Recording the family history and careful clinical evaluation are useful tools in the diagnosis. In case of genetic bases, definitive diagnosis requires molecular analysis. We report consanguineous two patients presenting with young-onset progressive dementia characterized by behavioral changes and with bone cysts. Concomitant bone pathology and inheritance pattern directed us to investigate TREM2 gene, for differential diagnosis, which resulted with the identification of a causative mutation that confirmed the diagnosis of Nasu Hakola disease. The mutation (c.113A>G) is the same for a Turkish family with Nasu Hakola disease reported before. But the presence of bone cysts and absence of epilepsy in our patients are the different findings. Molecular analysis should be considered in patients with young age onset behavioral and cognitive deficits, with white matter lesions in brain magnetic resonance imaging, if especially associated with cystic bone lesions.