GMDS and congenital heart disease: Based on the defined genotype, we attributed the severe mental retardation, congenital heart disease and craniofacial abnormalities observed in the patient largely to hemizygous expression of FOXC1, FOXF2 and GMDS genes within the 6p25.3-pter interval, although circumstantial evidence suggested that in vivo instability of the r6 chromosome exacerbated the severity of the phenotype.