The family with no fingerprints.

ISLAMABAD -- Apu Sarker was showing his open palm to me on a video call from his home in Bangladesh. Nothing seemed unusual at first, but as I looked closer I could see the smooth surfaces of his fingertips.

Apu, who is 22, lives with his family in a village in the northern district of Rajshahi. He was working as a medical assistant until recently. His father and his grandfather were farmers.

The men in Apu's family appear to share a genetic mutation so rare it is thought to affect only a small handful of families in the world: they have no fingerprints.

Back in the day of Apu's grandfather...