Identifying the sex of human preimplantation embryos in X-linked disease: amplification efficiency of a Y-specific alphoid repeat from single blastomeres with two lysis protocols.

Abstract

Preimplantation diagnosis involves detecting genetic defects in one or two blastomeres biopsied from cleavage stage embryos following a vitro fertilization (IVF). For X-linked recessive disease, identification of the sex of embryos allows transfer of only unaffected females. To examine how critical the preparation of the single blastomere is for amplification of a Y chromosome specific repeat sequence using the polymerase chain reaction (PCR), the incidence of amplification failure has been examined following two lysis protocols. Amplification of a Y alphoid repeat sequence from single blastomeres disaggregated from cleavage stage embryos was examined after either (1) lysis in distilled water and freeze-thawing twice or (2) a two-step lysis protocol involving an initial treatment in potassium hydroxide and dithiothreitol. Some of the embryos had been previously sexed by cleavage-stage biopsy and fluorescent in situ hybridization with X- and Y-specific probes. Amplification failure occurred in 6 of 50 (12%) and 4 of 60 (7%) single blastomeres from male embryos following lysis in distilled water or using the two-step protocol, respectively. Conversely, amplification from contaminating DNA occurred in 5 of 63 (8%) single blastomeres from female embryos and 6 of 94 (6%) of control medium-blanks. The incidence of amplification failure was improved but not eliminated using the two-step lysis protocol. At least two cells, therefore, would be necessary for accurate identification of males by amplification of Y-specific repeat sequences alone. Nevertheless, this protocol for preparing cleavage-stage blastomeres is likely to give more consistent amplification of any unique or repeat sequences.