A locus for familial skewed X chromosome inactivation maps to chromosome Xq25 in a family with a female manifesting Lowe syndrome

In mammals,X-linked gene products can be dosage compensated between males and females by inactivation of one of the two X chromosomes in the developing female embryos.X inactivation choice is usually random in embryo mammals,but several mechanisms can influence the choice determining skewed X inactivation.As a consequence,females heterozygous for X-linked recessive disease can mani- fest the full phenotype.Herein,we report a family with extremely skewed X inactivationt hat produced the full phenotype of Lowe syndrome,a recessive X-linked disease,in a female.The X chromosome inactivation studies detected an extremely skewed inactivation pattern with a ratio of 100:0 in the propositus as well as in five out of seven unaffected female relatives in four generations.The OCRL1‘‘denovo’’mutation resides in the active paternally inherited X chromosome.X chromosome haplotype analysis suggests the presence of a locus for the familial skewed X inactivation in chromosome Xq25 mostlikely controlling X chromo- some choice in X inactivation or cell proliferation.The description of this case adds Lowe syndrome to the list of X-linked disorders which may manifest the full phenotype in females because of the skewed X inacti- vation.