title: Cytogenetic profile in 1,921 cases of trisomy 21 syndrome.
abstract: OBJECTIVE
  Trisomy 21 is the most frequent genetic cause of intellectual disability. It is caused by different cytogenetic aberrations: free trisomy, Robertsonian translocations, mosaicism, duplication of the critical region and other structural rearrangements of chromosome 21. The aim of the study was to identify in Mexican trisomy 21 patients who attended Hospital Infantil de México Federico Gómez from 1992-2011 the type and frequency of the cytogenetic aberration and to evaluate the effect of maternal age.
  
  
  METHODS
  A retrospective analysis of epidemiological data and karyotype reports were carried out; type and frequency of the cytogenetic variants were determined.
  
  
  RESULTS
  We identified 2,018 cases referred with a clinical diagnosis of trisomy 21. In 1,921 analyses (95.2%) a cytogenetic variant of trisomy 21 was identified: free trisomy 21 in 1,787 cases (93.02%), four cases (0.21%) had an additional non-contributory aberration; Robertsonian translocations in 92 cases (4.79%); mosaicism in 31 cases (1.61%) and seven cases (0.36%) had other chromosomal abnormalities, five (0.26%) had other contributory structural rearrangements and two corresponded to double aneuploidies (0.10%). Gender distribution was 1,048 (54.56%) males and 873 (45.44%) females. A maternal age effect was observed in patients with free trisomy 21 with mothers >36 years of age.
  
  
  CONCLUSIONS
  The present work reports the experience of a Mexican referral center regarding the karyotype diagnosis of patients with trisomy 21 and is one of the most extensive studies published so far. Percentages of the cytogenetic abnormalities present in our population reflect the ones previously reported for these cytogenetic alterations worldwide.
authors: Departamento de Genética, Hospital Infantil de México Federico Gómez, México, D.F., México.
authors: Francisco
authors: F
authors: Flores-Ramírez
authors: Departamento de Genética, Hospital Infantil de México Federico Gómez, México, D.F., México; Servicio de Genética, Hospital General de México Dr. Eduardo Liceaga, Facultad de Medicina, UNAM, México, D.F., México.
authors: Claudia
authors: C
authors: Palacios-Guerrero
authors: Departamento de Genética, Hospital Infantil de México Federico Gómez, México, D.F., México.
authors: Constanza
authors: C
authors: García-Delgado
authors: Departamento de Genética, Hospital Infantil de México Federico Gómez, México, D.F., México.
authors: Ariadna Berenice
authors: AB
authors: Morales-Jiménez
authors: Departamento de Genética, Hospital Infantil de México Federico Gómez, México, D.F., México.
authors: Christian Martín
authors: CM
authors: Arias-Villegas
authors: Servicio de Genética, Hospital General de México Dr. Eduardo Liceaga, Facultad de Medicina, UNAM, México, D.F., México.
authors: Alicia
authors: A
authors: Cervantes
authors: Departamento de Genética, Hospital Infantil de México Federico Gómez, México, D.F., México. Electronic address: vfmoran@himfg.edu.mx.
authors: Verónica Fabiola
authors: VF
authors: Morán-Barroso
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003582:Cytogenetics / Q000379:methods*; D004314:Down Syndrome / Q000235:genetics* / Q000473:pathology; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D059785:Karyotype; D008297:Male; D008423:Maternal Age; D012189:Retrospective Studies; D055815:Young Adult
keywords: Chromosome 21; Down syndrome; Mosaicism; Robertsonian translocation; Trisomy 21