In its original French, My Brother Simple was a prizewinning best-seller. It was adapted for television in France, where its author, Marie-Aude Murail, is a household name.

All of which goes to show: the French, they ain’t like us.

Because My Brother Simple is a very odd book. It tells the story of 17-year-old Kleber, who takes responsibility for his older brother, nicknamed Simple, when their father attempts to put him in an institution. Simple is 22, but has the mental age of a three-year-old.

Simple’s misadventures are recounted in the episodic, one-adventure-per-chapter style of a primary school novel. Think My Naughty Little Sister, or anything by E. Nesbit. But this style of novel relies on actual adventure: something substantial needs to happen in every chapter. “Simple pees in a public swimming pool” does not qualify as something substantial.

Also, this is not a book for primary children. There is sex, smoking and a lot of swearing. Shoplifting and drunken partying are not topics that benefit from being tackled through jaunty children’s narration.

There is also - disturbingly - a lot of misogyny. A girl who likes to take control of relationships is dismissed as “aggressive” and “castrating”. One character is described purely in terms of her “substantial backside”. Kleber thinks “What the hell is that?” when he sees an unattractive woman, and is never forced to reconsider his reaction. In fact, he spends the entire book treating Zahra, who has a crush on him, like dirt. When he eventually sees the light, I desperately want her to turn around and tell him she can do better. She does not.

Worst of all, the book’s second romantic hero lashes out at the object of his affections: “You bitch! You little tease!” She falls for him nonetheless. Note to any 17-year-old boys reading this: act like that and you will never get laid. (Oh, how I wish that were true.)

In fact, Simple is almost the only likeable character in the entire book. This merely perpetuates the notion that people with learning difficulties are lovable and good-natured, rather than fully rounded human beings.

But the world of My Brother Simple is one of blacks and whites. People are smart or stupid; girls are pretty or ugly. Institutions are heartless and uncaring; the same applies to the people who put their relatives there. Love comes to those who wait. Everything works out for the best in the end.

If the entire book were intended as an oh-so-clever illustration of the world as seen through the eyes of someone with learning difficulties, it might deserve some of the prizes that have been heaped upon it. It isn’t. And it doesn’t.

My Brother Simple by Marie-Aude Murail, Bloomsbury #163;6.99.