Genetic Constraints on the Development of Alphabetic Literacy: A Cognitive Study of Two 48,XXXY Cases

We report a longitudinal study of literacy development in two boys, AT and HT, who presented with a sex chromosome abnormality (48,XXXY syndrome). Verbal IQ was severely depressed. Reading and spelling had peaked atan 8-year level. Neither boy had established an alphabetic process. Nonwords could not be read or written (although the individual letters of the alphabet were known). Phonological skills were only partially established and scores fluctuated considerably. Development appeared to have been almost exclusively logographic. An extensive word recognition vocabulary was supported. Both boys had developed special interests and appeared to be able to assimilate new reading vocabulary into these domains. Spelling was almost invariably dysphonetic but showed a tendency towards acknowledgement of graphotactic constraints. The results suggest thatgenetic syndromes may selectively constrain the acquisition of specific components of literacy.