• Coffin-Lowry syndrome
• complex chromosome rearrangement
• RSK2

The eponym Coffin-Lowry syndrome has been used by clinical geneticists for over a quarter of a century now, since first proposed by Temtamy et al¹ in 1975. The syndrome refers to a recognisable clinical condition, characterised by mental retardation, characteristic facial appearance, and skeletal abnormalities. Most geneticists would consider that the condition represents a fairly good example of “gestalt” diagnosis, the recognition of a familiar pattern on observing the face. Young² has tabulated the facial features in this condition, identifying coarseness, hypertelorism, antimongoloid slant, pouting, everted lower lips, and a broad nose as the most frequently observed features. In addition, affected subjects frequently have pectus excavatum/carinatum, kyphosis or scoliosis, and broad hands, often with tapering fingers and hypothenar crease.

Inherited as an X linked condition, the classical phenotype is described in affected males. However, carrier females frequently manifest clinical characteristics of the condition. Mapping of the locus indicated a location in Xp22.3-p22.1.³ Subsequently, disease causing mutations have been described in the ribosomal protein S6 kinase (RSK2).^4–6 A wide range of different types of mutations have been described, distributed throughout the gene, many associated with premature translation termination, and most associated with predicted loss of function of the mutant allele.⁶ The application of these findings in clinical practice has served not just to expand the understanding of the mutational basis of the classical syndrome, but has also shown that atypical, mild forms of Coffin-Lowry syndrome exist.⁷ Despite these occasional clinical surprises, most patients harbouring pathogenic mutations of the RSK2 locus have shown clinical characteristics consistent with those expected in Coffin-Lowry syndrome.⁵ However, as established by a recent mutational screen in 250 …