Teenager dyslexic only in English

English can be tougher on the brain than other languages, according to a scientist studying the case of a boy who struggles to read English primary school storybooks while wading through physics textbooks in Japanese.

The boy, 17, named only as AS, is believed to be the first person shown to be dyslexic in one language but not another.

He has English parents but lives in Japan. At the age of six, he went to a Japanese primary school but lagged behind his Japanese counterparts in English. When he was 13, tests confirmed that he was dyslexic.

While he can perceive English sounds accurately he can only read half as well as an average person of his age. Yet he has mastered the two written forms of Japanese - kanji, which consists of symbols which carry meaning but no phonetic value, and kana, whose symbols respond to particular sounds.

Researcher Taeko Wydell, of Brunel University, west London, told New Scientist magazine the case was difficult to reconcile with theories of dyslexia and could have "profound consequences for concepts of reading". New Scientist said: "The problem, she believes, lies in ... the English language's complex system of mapping sounds to letters, which gives rise to some eccentric spellings."