title: A de novo supernumerary genomic discontinuous ring chromosome 21 in a child with mild intellectual disability.
abstract: Small supernumerary marker chromosomes (sSMCs) are structurally abnormal extra chromosomes that cannot be unambiguously identified or characterized by conventional banding techniques alone, and they are generally equal in size or smaller than chromosome 20 of the same metaphase spread. Small supernumerary ring chromosomes (sSRCs), a smaller class of marker chromosomes, comprise about 10% of the cases. For various reasons these marker chromosomes have been the most difficult to characterize; although specific syndromes have not yet been defined, 60% of cases are associated with an abnormal phenotype. The chromosomal material involved, the degree and tissutal distribution of mosaicism, and the possible presence of uniparental disomy, are the important factors determining whether or not the ring chromosome will give rise to symptoms. Using conventional and molecular cytogenetics approaches we identified a de novo chromosome 21 sSRC in a child with speech delay and mild intellectual disability. By using aCGH analysis and SNP arrays, we report the presence of two discontinuous regions of chromosome 21 and the paternal origin of the sSRC. A thorough neuropsychiatric evaluation is also provided. Only few other cases of complex discontinuous ring chromosomes have been described in detail.
authors.affiliation: Medical Genetics Laboratory, S. Gerardo Hospital, Monza, Italy.
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Villa
authors.forename: Angela
authors.initials: A
authors.lastname: Bentivegna
authors.forename: Adam
authors.initials: A
authors.lastname: Ertel
authors.forename: Serena
authors.initials: S
authors.lastname: Redaelli
authors.forename: Carla
authors.initials: C
authors.lastname: Colombo
authors.forename: Renata
authors.initials: R
authors.lastname: Nacinovich
authors.forename: Fiorenza
authors.initials: F
authors.lastname: Broggi
authors.forename: Sara
authors.initials: S
authors.lastname: Lissoni
authors.forename: Silvia
authors.initials: S
authors.lastname: Bungaro
authors.forename: Sankar
authors.initials: S
authors.lastname: Addya
authors.forename: Paolo
authors.initials: P
authors.lastname: Fortina
authors.forename: Leda
authors.initials: L
authors.lastname: Dalprà
mesh_terms: D002648:Child; D002675:Child, Preschool; D055028:Comparative Genomic Hybridization; D019295:Computational Biology; D003582:Cytogenetics; D004314:Down Syndrome / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008607:Intellectual Disability / Q000235:genetics / Q000473:pathology*; D011596:Psychomotor Disorders / Q000235:genetics / Q000473:pathology*; D012303:Ring Chromosomes