title: Detailed analysis of X chromosome inactivation in a 49,XXXXX pentasomy.
abstract: BACKGROUND
  Pentasomy X (49,XXXXX) has been associated with a severe clinical condition, presumably resulting from failure or disruption of X chromosome inactivation. Here we report that some human X chromosomes from a patient with 49,XXXXX pentasomy were functionally active following isolation in inter-specific (human-rodent) cell hybrids. A comparison with cytogenetic and molecular findings provided evidence that more than one active X chromosome was likely to be present in the cells of this patient, accounting for her abnormal phenotype.
  
  
  RESULTS
  5-bromodeoxyuridine (BrdU)-pulsed cultures showed different patterns among late replicating X chromosomes suggesting that their replication was asynchronic and likely to result in irregular inactivation. Genotyping of the proband and her mother identified four maternal and one paternal X chromosomes in the proband. It also identified the paternal X chromosome haplotype (P), indicating that origin of this X pentasomy resulted from two maternal, meiotic non-disjunctions. Analysis of the HUMANDREC region of the androgen receptor (AR) gene in the patient's mother showed a skewed inactivation pattern, while a similar analysis in the proband showed an active paternal X chromosome and preferentially inactivated X chromosomes carrying the 173 AR allele. Analyses of 33 cell hybrid cell lines selected in medium containing hypoxanthine, aminopterin and thymidine (HAT) allowed for the identification of three maternal X haplotypes (M1, M2 and MR) and showed that X chromosomes with the M1, M2 and P haplotypes were functionally active. In 27 cell hybrids in which more than one X haplotype were detected, analysis of X inactivation patterns provided evidence of preferential inactivation.
  
  
  CONCLUSIONS
  Our findings indicated that 12% of X chromosomes with the M1 haplotype, 43.5% of X chromosomes with the M2 haplotype, and 100% of the paternal X chromosome (with the P haplotype) were likely to be functionally active in the proband's cells, a finding indicating that disruption of X inactivation was associated to her severe phenotype.
authors.affiliation: Genetics Division, Instituto Nacional de Câncer, Rio de Janeiro, Brazil. hseuanez@inca.gov.br.
authors.forename: Lucia M
authors.initials: LM
authors.lastname: Moraes
authors.forename: Leila Ca
authors.initials: LC
authors.lastname: Cardoso
authors.forename: Vera Ls
authors.initials: VL
authors.lastname: Moura
authors.forename: Miguel Am
authors.initials: MA
authors.lastname: Moreira
authors.forename: Albert N
authors.initials: AN
authors.lastname: Menezes
authors.forename: Juan C
authors.initials: JC
authors.lastname: Llerena
authors.forename: Héctor N
authors.initials: HN
authors.lastname: Seuánez