Research

Detailed analysis of X chromosome inactivation in a 49,XXXXX pentasomy

Lucia M Moraes¹ , Leila CA Cardoso^2,3 , Vera LS Moura¹ , Miguel AM Moreira² , Albert N Menezes^2,3 , Juan C Llerena Jr¹ and Héctor N Seuánez^2,3

¹  Medical Genetics Department, Instituto Fernandes Figueira, Fiocruz, Rio de Janeiro, Brazil

²  Genetics Division, Instituto Nacional de Câncer, Rio de Janeiro, Brazil

³  Department of Genetics, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil

author email corresponding author email

Molecular Cytogenetics 2009, 2:20doi:10.1186/1755-8166-2-20

Published:	7 October 2009

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.

Conclusion

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.