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Fragile X syndrome is the commonest inherited cause of mental retardation, with a prevalence of between 1 in 4000 to 1 in 6000 males. 1 2 Most cases are the result of amplification of a CGG trinucleotide repeat sequence located in the 5[variant prime] untranslated region of the FMR1 (FRAXA) gene on the long arm of the X chromosome. This sequence is unstable, a triplet repeat number of greater than approximately 200 causing inhibition of transcription of FMR1. Rarely, the clinical syndrome may result from deletion of all or part of the FMR1 (FRAXA) gene. 3 In three cases reported previously, the FMR2 (FRAXE) gene lying just distal to FMR1 was also deleted. 4-6 We describe a boy with a de novo deletion of the entire FMR1 and FMR2 genes and compare his features with those of the other reported cases.
Case report
The patient was born after an uneventful pregnancy by elective caesarian section for breech presentation. His birth weight was 4692 g and there were no perinatal problems. There was no relevant family history. Severe developmental delay became evident in the first year of life. He sat at 10 months and walked at 2 years 10 months. Now aged 13 years, he can speak in short sentences and has behavioural difficulties, with aggression and agitation. He also has autistic features including a dislike of change in routine and hand flapping. Since 2½ years he has had severe polymorphic epilepsy which has been difficult to control despite several anticonvulsant medications.
On examination, he has a large head (circumference above...