Cloning using somatic cells has potentially important clinical and therapeutic applications, but the long-term effects of cloning on the offspring of these animals remains unknown. In March Nature Medicine, Kellie Tamashiro and colleagues from University of Cincinnati College of Medicine, Ohio, USA, show that cloned mice have an obese phenotype, but that this is not transmitted to their offspring.

Tamashiro et al. examined cloned mice of different background strains (B6C3F1, B6D2F1) and used specific control groups and conditions to analyze their metabolic characteristics. They found that adult cloned mice are not only heavier but also have a spectrum of behavioral and metabolic alterations consistent with obesity. But, the obese phenotype was not transmitted to offspring generated by mating male and female cloned mice (Nat Med 2002, 8:262-267).

These findings "provide further evidence that cloned embryos are vulnerable to epigenetic change" wrote Ian Wilmut from Roslin...