PLOSL is an adult-onset recessively inherited disorder of bones and central nervous system leading to early dementia and death. Onset of clinical disease occurs in the third decade of life with pain and swelling following strain of the wrist and ankle. Fractures may occur after minor accidents. Radiographs show cystic rarefactions in the epiphyseal regions of bones. The cysts contain jelly-like material. Neuropsychiatric symptoms begin after age of 30 years presenting progressive dementia with an accentuated prefrontal syndrome, signs of upper motor neuron involvement, agnostic-aparactic-aphasic symptoms, myoclonic jerks and epileptic seizures. Death occurs before the age 50. Blood vessels of affected organs have thickened basement membranes. PLOSL should be considered in young adults showing multiple cysts in bones and varied neurological symptoms. Mutations causing PLOSL have been identified in two different genes, DAP12 and TREM2. Mutations in these two genes lead to an identical phenotype. However, recent data also indicates that some mutations in TREM2 can lead to pure early-onset dementia without bone cysts.