Savant syndrome, a paradox of both mental deficiency and superiority, has been a consuming interest of American psychiatrist Darold Treffert for 47 years. A book by such an authority should be welcomed but unfortunately, despite its authorship, Islands of Genius is disappointing.

It is not that the subject is dull. Any comprehensive theory of human brain function will need to take into account the existence of savants and the talents of prodigious savants are extraordinary. Kim Peek, who partly inspired Dustin Hoffman’s character in the film Rain Man, memorised 12 000 books during his lifetime. A century earlier the celebrated musician Thomas Bethune had a repertoire of 7000 pieces despite a vocabulary of only 100 words. The book is rich in detail and thorough enough to satisfy all but the most curious. It is also not afraid to explore the subject’s boundaries although, where evidence is lacking, Treffert has a tendency to concentrate on his pet theories rather than adopting a more balanced approach. He never writes of savants as simply curiosities and the tenderness with which he relates their stories and those of their carers could serve as an example to us all. In part, this book is a championing of their cause: Treffert is critical of IQ scores, for example, which he considers do a disservice to savants and he is at pains to point out that savants can be creative in addition to having extraordinary memory and calculation skills.

Unfortunately, a sentimental streak is often evident in Treffert’s writing and this comes close to overwhelming the book’s other strengths. This is most marked where savant case histories are presented. These 14 chapters are superlative-laden and their personal-triumphs-against-adversity narratives would be more suited to a glossy magazine. Regrettably, they take up a third of the book. They also sit uncomfortably with earlier chapters about neuroscience, which are predominantly academic in delivery, and later chapters, by guest contributors, which concern the beneficial effects resulting from ‘training the talent’ of savants. This diversity of styles and subjects leaves one wondering for whom the book is actually intended.