Editor—Microphthalmia with linear skin defects (MLS) is a clinically complex and highly variable phenotype in XX subjects and has been considered to be at least partially determined by three features: the pattern of X chromosome inactivation; the extent of the Xp22.3 segmental monosomy; and the nature of the chromosomal anomaly (deletion or translocation).The recurring features of microphthalmia with linear skin defects, generally restricted to the face and neck in all the early reported cases, led to its designation as the MLS syndrome. The consistent association of these two manifestations with Xp22.3 segmental monosomy suggests that MLS is a contiguous gene syndrome.1 ,2However, the phenotype may be complicated by additional abnormalities which include sclerocornea, chorioretinal abnormalities, agenesis of the corpus callosum, hydrocephalus, infantile seizures, mental retardation, and congenital heart defects. To date, around two dozen cases of MLS syndrome (including our case) have been published and in approximately half (including our case), the Xp22.3 disruption has resulted from a terminal deletion.3-10 In the remaining cases, Xp22.3 segmental monosomy is a consequence of X;Y8 ,11-13 or X;autosome translocations.14-18

In all cases, there is monosomy for over 10 megabase pairs and comparison with patients harbouring smaller deletions has defined a ∼570 kb interval that must contain the gene(s) giving rise to the diagnostic clinical features of the disorder, including microphthalmia, sclerocornea, and linear skin defects. Subsequent and ongoing investigations have led to the identification and characterisation of three genes from this minimal region as well as the precise mapping of a number of expressed sequence tags (ESTs). However, it is still currently unknown which gene(s) are responsible for this unique combination of features. Wapenaar et al 19 ,20 used cell lines from 10 MLS cases with deletions and translocations involving the Xp22 region to …