Analysis of host genetic control of scrapie-induced obesity

On the track of the white tiger: pigmentation could be linked to prion diseases, and location explains why

Certain rodent pigmentation mutants spontaneously develop brain spongiform changes. It is hypothesized that animals, and possibly humans, characterized by certain pigmentation gene variants could be more susceptible to prion diseases, which are characterized by this type of neuropathology. This hypothesis could be explained by the common location of the prion protein and several important pigmentation genes in the same chromosome. This common location can promote the joint transfer of both pigmentary and prion protein genes to the progeny. Pigmentation genes could also play a role in regulating protein folding and aggregation. Understanding the relationship between pigmentation genes and prion genes could lead to identify pigmentation variants at higher risk of prion diseases and understand the etiopathogenesis of these still invariably lethal disorders.

Viruses as an etiology of obesity

Obesity is a serious chronic disease that has numerous etiologies. The prevalence of obesity has increased dramatically since about 1980 in the United States and worldwide in both developed and developing countries. This rapid spread is compatible with an infectious origin. This review discusses the 5 animal viruses and 3 human viruses that have been shown to cause obesity and examines the evidence to date for virus-induced obesity. The obesogenic animal viruses include canine distemper virus, Rous-associated virus type 7, Borna disease virus, scrapie agent, and SMAM-1. The first 4 viruses attack the central nervous system to produce obesity. SMAM-1, an avian adenovirus from India, acts directly on adipocytes and is the only animal virus that is associated with human obesity. The 3 human adenoviruses, adenovirus (Ad) 36, Ad-37, and Ad-5, that are associated with obesity also affect adipocytes directly. These viruses stimulate enzymes and transcription factors that cause accumulation of triglycerides and differentiation of preadipocytes into mature adipocytes. Ad-5 and Ad-37 have been shown to cause obesity in animals. Ad-36 has been studied the most and is the only human adenovirus to date that has been linked with human obesity. Ad-36 causes obesity in chickens, mice, rats, and monkeys and was present in 30% of obese humans and 11% of nonobese humans. In twins discordant for infection with Ad-36, the infected twins were heavier and fatter than their cotwins. The growing body of evidence demonstrating that viruses produce human obesity supports the concept that at least some of the worldwide epidemic of obesity in the past 25 years is due to viral infections.