We describe a maternally transmitted genomic-imprinting syndrome of mental retardation, hypotonia, and unique dysmorphism with elongated face. We mapped the disease-associated locus to approximately 7.27 Mb on chromosome 8q24 and demonstrated that the disease is caused by a missense mutation in the maternal copy of KCNK9 within this locus. KCNK9 is maternally transmitted (imprinted with paternal silencing) and encodes K(2P)9.1, a member of the two pore-domain potassium channel (K(2P)) subfamily. The mutation fully abolishes the channel's currents--both when functioning as a homodimer or as a heterodimer with K(2P)3.1.

Five unrelated patients (a male and 4 females) were affected with a previously undefined multiple congenital anomalies/mental retardation syndrome which has been designated the facio-cutaneous-skeletal (FCS) syndrome and which includes mental retardation with specific sociable, humorous behavior, characteristic facial appearance, excessive generalized skin, postnatal growth failure, and skeletal involvement. Consanguinity was noted in 2 patients, thus autosomal recessive inheritance is suggested.

The clinical diagnosis of ASS (Aarskog-Scott syndrome or Faciogenital Dysplasia) was made in seven individuals belonging to a large Arabic family, which was supported by molecular studies revealing a 2189delA mutation in exon 15 of the FDG1 gene. The affected individuals in this family demonstrated clinical variability particularly in their cognitive skills, raising the question whether other genetic factors might be involved in the phenotypic evolution of ASS.

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