48,XXXX-49,XXXXX mosaic: asynchronies among the late-replicating X chromosomes

Tetrasomy and pentasomy of the X chromosome

We describe a newborn girl with a life-threatening laryngomalacia and extreme hypotonia. Genetic analysis revealed the very rare genetic condition mosaicism of 48,XXXX and 49,XXXXX (50/50). We here state that the degree of early hypotonia constitutes an important early prognostic feature in this syndrome. The timely insertion of a gastrostomy is warranted in order to prevent aspiration.

CONCLUSION

A karyotype is mandatory in female newborns with moderate to severe hypotonia in order to exclude polyploid mosaicism of the X chromosome. An 'overall prognosis' for 48,XXXX and 49,XXXXX girls is difficult to provide towards parents in line with a well-known, substantial variability in outcome for all polysomy X infants.

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.

Sex differences in lingual marginal ridging on the human maxillary central incisor

Although incisor dimensions are on average larger in males, at least one incisor trait, lingual marginal ridging, is significantly more common in females. This is documented for the upper central incisor in a collation of 38 samples of living populations representing six racial groups. Caucasian, Asian, Polynesian, Melanesian, and American Indian females each possess significantly higher frequencies than their male counterparts. American Blacks do not show a sex difference. Sex differences in the duration and rate of incisor crown development do not explain this dimorphism. Possible underlying genetic causes are reviewed, and the hypothesis is proposed that relevant portions of both X chromosomes in females are contributing to greater trait expression.

Human X chromosomes: synchrony of DNA replication in diploid and triploid fibroblasts with multiple active or inactive X chromosomes

We have analyzed patterns of DNA replication in X chromosomes from diploid cultured human fibroblasts and from three triploid 69,XXY fibroblast strains, using BrdU--33258 Hoechst--Giemsa techniques. Both X chromosomes in each of these Barr body-negative triploid strains were early-replicating. The results of gene dosage studies using (1) a histochemical stain to measure X-linked glucose-6-phosphate dehydrogenase (G6PD) activity in single cells and (2) cellulose acetate electrophoresis of G6PD activity in cell extracts also indicated that both Xs in these strains were genetically active. When we compared the synchrony of X chromosome DNA replication kinetics both between cells and within cells containing multiple inactive Xs, a marked variability and asynchrony was observed for late-replicating X chromosomes. In a culture of 47,XXX fibroblasts administered an 8-h terminal pulse of dT after growth in BrdU-containing medium, asynchrony was detected between the two late-replicating Xs in approximately 70% of cells examined. No such asynchrony was observed between the two early-replicating Xs in similarly cultured 69,XXY cells; in the triploid strains, the two Xs were distinguished by asynchronous replication in only approximately 15% of cells. The striking variability in late X chromosome replication kinetics appears, then, to be a property unique to inactive Xs and is not inherent to all X chromosomes.

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.

BrdU-33258 Hoechst analysis of DNA replication in human lymphocytes with supernumerary or structurally abnormal X chromosomes

BrdU-33258 Hoechst techniques have been used to characterize DNA replication patterns in lymphocytes from hunam females with supernumerary or structurally abnormal X chromosomes. Fluorescence analysis permits identification of late replicating X chromosomes in a very high proportion of cells and affords a high resolution method for determining the interchange points of X-X and X-autosome translocations. Asynchrony among terminal replication patterns of multiple late replicating X chromosomes within an individual cell can occasionally be demonstrated. The arms of isochromosomes usually exhibit symmetrical fluorescence patterns, with replication terminating in bands Xq21 and Xq23 (predominant pattern) or in bands Xq25 and Xq27 (alternative pattern) in both arms. In the vast majority of lymphocytes containing a balanced X-13 or X-19 translocation, the normal X is late replicating. However, DNA synthesis in the translocation products occasionally appears somewhat delayed relative to that expected for an early replicating X, consistent with possible position effects on replication kinetics.

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

Images