Evaluation Of PGD Reliability In Microduplications Based On Diverse Etiology Of Formation

Introduction: Couples carrying pathogenic microduplication can opt for PGD to prevent an affected offspring. PGD lab is then challenged to detect the extra copy in a feasible and reliable manner.

Aim: To categorize the types of microduplication in order to evaluate the feasibility and reliability of PGD based on the distances between the duplicated sequences and the mechanisms for the duplication`s formation.

Material and Methods: Seven cases of microduplication carriers opted for PGD. In order to evaluate the reliability of the diagnosis, duplication cases were categorized into 4 classes based on FISH analysis using probes tailored to the duplicated region and haplotype analysis with informative polymorphic markers within this region. Subsequently, whenever the detection methods were sufficiently accurate, IVF-PGD cycles were performed.

Results: Four categories were defined based on FISH and Haplotype analysis. In the first category two FISH signals were observed in > 90% of interphase cells, hinting for tandem duplication. In the second one, 3 FISH signals were observed in more than 30% of the cells, suggesting close but not tandem duplication. Distant duplications were determined by 3 totally separated FISH signals. Haplotype analysis of these 3 categories demonstrated only 2 alleles. The 4th category of close but not tandem duplication with 3 different alleles was demonstrated by haplotype analysis in CMT1A patients only.

Conclusions: We suggest that only tandem and/or 3 different allele`s duplications can be reliably diagnosed by PGD using haplotype analysis. In other cases PGD is not reliable enough and should be avoided.