The skinny on fat cats
By Bianca Haase
Obesity in humans is an escalating global health problem leading to increased mortality and comorbidities. It is associated with multiple diseases, particularly type 2 diabetes (T2D), cardiovascular diseases, obstructive sleep apnea, and osteoarthritis. Cats are among the most common household pets and they share the same environment with humans and thus many of the risk factors. Obesity is a growing problem for feline health for the same reasons as it is in humans and has become a serious veterinary problem. Multiple diseases, such as type II diabetes mellitus and dermatosis, are associated with excess body weight and obesity in cats and may result in a lowered quality of life and potentially lead to an early death. Appleton et al. demonstrated that about 44% of cats developed impaired glucose tolerance (pre-diabetes) with obesity. The prevalence of being overweight in cats has been estimated to vary between 6% and 52%. The most recent published study about the prevalence of obesity in cats classified 19% of cats as being overweight and 7.8% to be obese. The incidence of diabetes in cats is increasing for the same reasons as it is in humans – a decrease in activity and an increase in body weight. Risk factors such as castration, indoor housing and access to highly palatable food, lead to increased food intake and/or physical inactivity, resulting in a positive energy balance and finally in above-average body weights.
A striking overweight phenotype could be observed in an experimental cat population hosted at the Institute of Animal Nutrition, Vetsuisse Faculty, Switzerland. As all cats share common housing facilities and fed similarly, environmental factors can most likely be excluded as the cause for this observation. Differences in feeding behavior due to the order of precedence could also be excluded as at least two feeding places were available in each group. Preliminary investigations on a subset of cats revealed significant differences between the two observed phenotype classes. In lean cats an average body fat content of 8.0% (± 1.6%) was observed, whereas overweight cats had an average body fat content of 25.6% (± 1.3%). As the two phenotypic groups were clearly distinguishable from each other, the result prompted us to hypothesize that a single major gene may be responsible for a large fraction of the observed variation in body composition.
To test for the mode of inheritance all cats were classified into overweight and lean groups according to their lean body mass. A computer based complex analysis confirmed our hypothesis that a major genetic component is responsible for the observed phenotypic difference and that the condition is heritable. As a next step it is now necessary to identify the putative gene with large impact on body composition in cats. The new feline 70k genotyping array will allow testing of about 70.000 variable positions in a cat’s genome and will give a high resolution genome map. Testing all individuals belonging to the experimental cat population will allow map comparisons between the two phenotypic classes. This comparison will highlight genomic regions that differ between the two groups. Subsequently, these regions will be further analyzed.
The study represents an international team effort including recognized experts with substantial expertise in clinical manifestation of the phenotype, nutritional and metabolic aspects of the condition as well as strong genome analysis expertise. The chance of revealing causal genetic factors regulating bodyweight in cats can be rated very high. Identification of a causative mutation would allow genetic testing to facilitate the breeding of healthier cats. A better understanding of the control of body mass may also highlight better management options, such as diet.
If you’re interested in learning more, the complete research of Haase et al. has been made available free online by the Journal of Heredity.