All non-primate mammals can develop 'large offspring syndrome' when cloned because they have only one functional copy of insulin-like growth factor II receptor (M6P/IGF2R). This is due to a rare phenomenon known as genomic imprinting, in which the M6P/IGF2R gene is stamped with markings that turn off its function. But in August Human Molecular Genetics Keith Killian and colleagues from Duke University Medical Center show that in humans, genomic imprinting for M6P/IGF2R does not occur, theoretically making humans technically easier to clone than sheep and other nonprimates.