Comparative clinical studies and X chromosome behaviour in a case of XXXX-XXXXX mosaicism

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

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.

Pentasomy X: report of patient and studies of X-inactivation

A five-year-old girl presented with mental retardation (MR), microcephaly, short stature, ptosis, malocclusion, abnormal elbows, fifth finger clinodactyly, joint hyperextensibility in hands and feet, renal hypoplasia, nonobstructive ureteral stasis, pyelonephritis, and renal failure. Five X chromosomes (49,XXXXX) were found in all peripheral blood lymphocytes and skin fibroblasts examined. Xa RBC typing, utilizing serial dilutions of antiserum, gave agglutination at a higher titer than in either Xg(a+) positive parent; the patient's serum IgM was also elevated. These immunological findings imply a lack of dosage compensation and incomplete inactivation of some X-linked loci.

The penta-X syndrome

A child is presented with a 49,XXXXX chromosomal constitution bringing to 12 the total number of children described with this karyotype. Comparison of this child's features with previously reported cases indicates a clinically recognisable specific pattern of malformations referred to as the penta-X syndrome. X chromosome replication studies using BrdU labelling in the patient's cells clearly showed that the four presumably inactive X chromosomes were late replicating but not in a strictly synchronous fashion.

Brief clinical report: renal hypodysplasia and unilateral ovarian agenesis in the penta-X syndrome

We report the case of a 3-year-old penta-X female with two previously undescribed anomalies: hypoplastic kidney and absent ipsilateral ovary. The gross and histologic structure of the contralateral ovary was normal, suggesting that adults with this syndrome may be fertile.