Washington, July 29 (IANS) An analysis of rare genetic disorders in which children lack some genes from one parent shows that maternal and paternal genes engage in a subtle tug-of-war well into childhood.
This striking new variety of intra-family conflict is the latest wrinkle in the two-decades-old theory known as genomic imprinting, which holds that each parent contributes genes that seek to nudge his or her children’s development in a direction most favourable.

“Compared to other primates, human babies are weaned quite early, yet take a very long time to reach full nutritional independence and sexual maturity,” said study author David Haig, professor of organismic and evolutionary biology at Harvard University.

“Human mothers are also unusual among primates in that they often care for more than one child at a time. Evidence from disorders of genomic imprinting suggests that maternal and paternal genes may skirmish over the pace of human development,” he said.

“Clinical data from imprinting disorders suggest paternally-expressed genes promote, and maternally-expressed genes inhibit, childhood growth,” Haig writes.

“This analysis suggests that human life history, and especially humans’ unusual extended childhood, may reflect a compromise between what’s best for mothers, fathers, and the offspring themselves,” Haig said.

Haig delved into clinical case reports on patients with four rare genetic disorders. He found evidence that children with disorders characterised by dominance of some maternal genes — Silver-Russell syndrome, Prader-Willi syndrome, and Temple syndrome — place fewer demands on their mothers’ resources.

For example, newborns with all three disorders display a weak desire to nurse, and slower childhood growth in general. Many also show early onset of puberty, which often marks a point at which children become less dependent on their mothers’ sustenance.

Conversely, babies with Beckwith-Wiedemann syndrome, in which some maternally derived genes are suppressed and paternal genes dominate, are born heavy with particularly large tongues.

These individuals usually end up being tall, owing to their rapid growth both in the womb and as young children. They have a high frequency of childhood cancers, said a Harvard release.

These findings were published this week in the Proceedings of the National Academy of Sciences.