title: A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13.
abstract: We describe two brothers with a unique pattern of malformations that includes coloboma (iris, optic nerve), high forehead, severe retrognathia, mental retardation, and agenesis of the corpus callosum (ACC). Both boys have low-set cupped ears with sensorineural hearing loss, normal phallus, pectus excavatum, scoliosis, and short stature. One brother had choanal atresia and cardiac defects consisting of ventricular septal defect (VSD) and patent ductus arteriosus (PDA) which resolved spontaneously. Differential diagnosis between a number of clinical entities was considered, however, because ACC and the distinctive facial features were reminiscent of FG syndrome, DNA was analyzed for markers linked to the FGS1 locus at Xq13-q21. Notably, the brothers were concordant for markers spanning this presumed FG region, and in both we have identified adjacent alterations (-57delT and T-55A) in the Alpha 4 gene located within this interval. Alpha 4 is a regulatory subunit of the major cellular phosphatase, PP2A, that has recently been shown to interact with MID1, the product of the gene mutated in X-linked Opitz GBBB syndrome. The double nucleotide change identified in this family was not observed in 410 control chromosomes, suggesting that it may be a pathogenetic change. Altered expression of Alpha 4, through either a change in translational efficiency, mRNA stability or splicing, could explain the clinical phenotype in these boys and the phenotypic overlap with Opitz GBBB syndrome.
authors.affiliation: Medical Genetics Birth Defects Center, Ahmanson Department of Pediatrics, Cedars-Sinai Medical Center, UCLA School of Medicine, Los Angeles, California 90048, USA. john.graham@cshs.org
authors.forename: John M
authors.initials: JM
authors.lastname: Graham
authors.forename: Patricia
authors.initials: P
authors.lastname: Wheeler
authors.forename: Darci
authors.initials: D
authors.lastname: Tackels-Horne
authors.forename: Angela E
authors.initials: AE
authors.lastname: Lin
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Hall
authors.forename: Melanie
authors.initials: M
authors.lastname: May
authors.forename: Kieran M
authors.initials: KM
authors.lastname: Short
authors.forename: Charles E
authors.initials: CE
authors.lastname: Schwartz
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Cox
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000293:Adolescent; D061085:Agenesis of Corpus Callosum; D001483:Base Sequence; D003103:Coloboma / Q000235:genetics*; D003937:Diagnosis, Differential; D040181:Genetic Diseases, X-Linked / Q000235:genetics*; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics*; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008844:Micrognathism / Q000235:genetics*; D018832:Molecular Chaperones; D009154:Mutation; D010375:Pedigree; D010750:Phosphoproteins / Q000235:genetics; D013577:Syndrome
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C490467:IGBP1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D018832:Molecular Chaperones; D010750:Phosphoproteins