In his bestselling autobiography Dreams from My Father Mr Obama recalls how, during his first visit to Kenya, his cousin referred to an uncle, Omar, who had left Africa and moved to Boston, but had been “lost”.

A little later in the book Mr Obama travels to the family village in western Kenya where he meets his step-grandmother, Sarah, the woman who had raised his father. On the walls of her tin-roofed hut, Mr Obama noticed photographs of the missing Omar, “the uncle who had left for America twenty-five years ago and had never come back”. (These photographs have since been removed.)

The woman he calls “Granny Sarah” was plainly anxious for news of her son, the half-brother of Mr Obama’s father. “Her only real problems were the roof of her house,” he writes, “and the fact that she had not heard from her son Omar in over a year. She asked if I had seen him, and I had to say no.”

Granny Sarah then made a remark in the Luo language, which a cousin translated for the American visitor. “She says when you see him, you should tell him she wants nothing from him . . . Only that he should come visit his mother.”

Mr Obama’s visit to Kenya took place in 1988. Dreams from My Father was first published in 1995. Had he been in contact with his missing uncle in the intervening years? Had he passed on his grandmother’s message?

Earlier this year The Times asked Mr Obama’s Kenyan family whether they had received any news of this missing relative in the US. Sayed Obama, another uncle and the family’s unofficial spokesman, insisted that he knew of no relative named Omar.

The other person who features prominently in Mr Obama’s book but had since disappeared was his Aunt Zeituni.

In the book he describes how, on his visit to Kenya, Zeituni revealed the mysteries of their complex family tree, introduced him to other relatives and fed him a herbal remedy for a stomach upset.

Zeituni had been working at Kenya Breweries when Mr Obama visited the country in 1988, but inquiries as to her whereabouts today elicited a similarly blank response from the family.

Zeituni, like the missing Omar somewhere in America, had apparently vanished.

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