Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
Board

In about 99% of the cases where 45,X karyotype is present at the time of human conception, a natural miscarriage occurs in the first stages of embryonic development. Only 1% of these fertilizations is taken successfully to term and generally displays the characteristics of Turner's syndrome (sexual infantilism, 'Pterigium colli' and 'cubitus valgus'; difficulties with space-form, numerical concepts and other features). The high percentage of foetal and embryonic miscarriage for karyotype 45,X points to 'the necessity of mosaicism for survival'. Natural selection does not always prevail when mosaicism is operative, although the resulting phenotype is similar. According to this hypothesis, we have carried out a genetic study of mosaicism in 41 TS patients. The investigation was carried out in four phases: cytogenetics (G-banding), FISH, PCR and SRY gene sequencing. The application of FISH and PCR techniques allowed us to find a second cellular line in 37 out of 41 patients, about 90%; only four patients (10%) were defined as non-mosaics. The most frequent mosaic was 45,X/46,XX (32%); the presence of isochromosomes comprised 27% and fragments 10%. The Y chromosome was present in blood and in ovarian tissue in two patients. The sequencing of the SRY gene showed a new mutation within the conserved binding motif of this gene consisting of a C to T transition that causes a conservative change from Arg (CGA) to stop codon (TGA) presumably giving rise to a truncated and probably non-functional SRY protein. In conclusion, our FISH and PCR results of mosaicism support the hypothesis of 'the necessity of mosaicism for survival', and thus, a mitotic origin of this syndrome.

Back to the top.
Poster Number PAfernández 0514
Keywords: turner's syndrome, mosaicism, Y-chromosome, sry, fish