RESULT(S): A majority (51%) of the conditions had clinical onset between infancy and adolescence ( Fig. 1A & 1B). Surprisingly, 29% of PGT-M conditions were of adult onset, and only 20% were congenital. One third (33%) of the conditions had reduced penetrance. The severity of most conditions was categorized as high (60%), but a significant fraction of conditions was for medium severity (22%) or even low severity (18%). Treatment could alter onset or progression in 60% of conditions. Nearly half (47%) of the PGT-M conditions had autosomal recessive inheritance, whereas 34% were autosomal dominant and only 19% were Xlinked. One hundred and thirty (130, 26%) couples presented with expanded carrier screening results. Overall, PGT-M was pursued for 167 (32%) conditions without any prior family history. Thirty-one (31, 6%) couples elected to pursue PGT-M for a VUS.CONCLUSIONS: The conditions for which patients are electing PGT-M have become increasingly complex since the inception of the test. Clinicians should be aware that not all genetic mutations are deterministic or predictive of disease severity. PGT-M may be utilized to prioritize embryos rather than to select and exclude. Genetic counseling to support decision making, both pre-test and post-test, is an essential part of a patient's reproductive journey.FINANCIAL SUPPORT: Authors are employees of, or previous interns at, the reference laboratory.Reference: 1. Rolland JS, Williams JK. Toward a biopsychosocial model for 21 st -century genetics. Fam. Process 2005; 44:3-24.

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