[Epidemiology of Idiopathic Normal Pressure Hydrocephalus and Hereditary Hydrocephalus]

Several cohort studies in Japan have revealed that the prevalence of idiopathic normal pressure hydrocephalus(iNPH)is around 1.6% among the elderly population(≧ 50 years old). The incidence of iNPH from the Yamagata(Takahata)cohort was 1.2/ 1,000 person-years in the elderly population. Although the Japanese guidelines for iNPH clearly describe the definition of "possible iNPH with MRI support," it is still difficult to find out not only patients with iNPH but also individuals in its preclinical stage with radiological findings of asymptomatic ventriculomegaly with features of iNPH on MRI(AVIM)or asymptomatic ventricular enlargement(AVE). It is assumed that only less than 10% of patients with iNPH were referred to hospitals in Japan. Several genes associated with congenital hydrocephalus have been found, including ciliopathy-related genes that directly affect the ependymal cilia in ventricles. Loss of the copy number of SFMBT1 was found to be a risk factor for iNPH. Knowledge about risk genes and their mechanisms in congenital and familial NPH may be a clue for the further understanding of the pathophysiology of iNPH.