Hyperlexia

Silberberg and Silberberg (1967) defined the term 'hyperlexia' to describe children who read at levels beyond those expected for their mental age in the face of disordered oral communication. Turkeltaub et al. (2004) stated that there are 3 consistent features of hyperlexia: the presence of a developmental disorder of communication, most often an autistic spectrum disorder (209850); acquisition of reading skills prior to age 5 years without explicit instruction; and advanced word recognition ability relative to mental age, with reading comprehension on par with verbal ability.

Among a group of 66 children with autism, Burd et al. (1985) identified 4 with hyperlexia.

Burd and Kerbeshian (1988) described a brother and sister who began reading at about age 3 before receiving instruction and spent much time thereafter reading from encyclopedias, dictionaries, almanacs, and newspapers at ages 4 to 6. Both were thought to have 'pervasive developmental disorder,' which includes autism and Tourette syndrome (137580).

Using functional MRI (fMRI) to study a 9-year-old boy with hyperlexia during covert reading, Turkeltaub et al. (2004) found greater activity in the left inferior frontal and posterior superior temporal cortical areas, and in the right inferior temporal cortical areas compared to controls. The authors suggested that precocious reading simultaneously draws on both left hemisphere phonologic and right hemisphere visual systems. The boy's reading comprehension ability fell in the average range, despite his advanced word decoding rate and accuracy and high IQ, further suggesting a diversion of attention resources from semantic aspects of reading to phonologic and visual aspects. Turkeltaub et al. (2004) noted that dyslexia (see 127700) had been associated with hypoactivation of the left superior temporal cortex.