[Muro disease: amyotrophic lateral sclerosis/parkinsonism-dementia complex in Kii peninsula of Japan]

Abstract

Muro disease refers to the endemic amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia complex (PDC) in the high incidence ALS focus in the Muro district of the Kii peninsula. Kii paralysis was first described in the 1680s in a folk literature, and as ALS in the medical literature by Kin-no-suke Miura in 1911. Two high-incidence ALS foci were discovered in 1960s by Kimura and Yase, and retro- and anterospective epidemiological surveys were started. Kii ALS was neuropathologically characterized by classical ALS pathology together with many neurofibrillary tangles (NFTs) in the brain, similar to Guamanian ALS. The incidence rates of ALS dramatically declined during the 1950s and 1980s, resulting in the disappearance of the high-incidence foci. In the early 1990s, however, Kuzuhara found existence of high-incidence of ALS in the region, and, in addition, of a high-incidence of PDC with abundant NFTs, similar to Guamanian PDC. The incidence rates of PDC dramatically rose during the 1980s and 1990s, and PDC replaced ALS. Unsuccessful attempts were made to identify cause and pathogenesis of the disease in minerals and environmental factors. More than 70% of patients in the endemic region had a family history of ALS or PDC; therefore, genetic factors were suspected as the cause. The authors analyzed the causative and risk candidate genes in the affected and unaffected family members, but failed to find genes related to ALS/PDC. The changing pattern of Muro disease from ALS with a younger onset and rapid progression to PDC with a later onset and longer survival suggests that some unknown environmental factor(s) might modulate the disease process, which basically might be programmed in the gene(s).