Microduplications in chromosome Xq28, which include the methyl-CPG binding protein (MECP2) gene, cause severe X-linked mental retardation. Serious recurrent infections are a feature of this condition. Affected males are micro or normocephalic. We report two normocephalic brothers with an approximately 0.5 Mb duplication which includes MECP2 who had rapid head growth in infancy. The younger boy had chronic constipation until the age of 3 years. For both boys, the susceptibility to infection subsided in the second year of life. Whether or not rapid head growth in infancy and/or constipation are frequent features of the phenotype remains to be seen as more patients are described. Susceptibility to infection can remit after early childhood and could theoretically be related to overexpression of the interleukin 1 receptor-associated kinase IRAK1 gene.