Variable expressivity in Patau syndrome is not all related to trisomy 13 mosaicism

Patau syndrome (trisomy 13) is very rare in live-born babies. Individuals with this chromosomal syndrome have a short lifespan and are rarely seen beyond infancy. This study is aimed at the clinical spectrum, natural history, and survival of patients with trisomy 13. We reviewed the detailed data of 13 Patau syndrome live-born babies. Among them two individuals were delivered from continuation of pregnancy even after prenatal diagnosis. The remaining 11 patients were born to younger mothers who did not undergo amniocentesis because no major anomalies except for cleft lip/palate were found on prenatal sonograms. The common features of Patau syndrome including the clinical triad (microphthalmia, cleft lip/palate, and polydactyly) and non-cyanotic heart defects were always found in our series. However, certain serious central defects (holoprosencephaly, omphalocele, and single umbilical artery), which are easily recognized from prenatal sonogram, occurred less frequently than those stated in the literature. The median survival time was 95 days and was longer than that previously reported. There were two infants with trisomic mosaicism with different outcomes in both clinical spectrum and survival. Otherwise, we also found the increased recurrence risks of aneuploidy in two individuals, and the longest survivor (84 months) of non-mosaic trisomy 13 in Taiwan. We thus suggest that long-term survival in our series is strongly correlated with different expressivity after prenatal selection, in addition to cytogenetic mosaicism. Less associated anomalies such as polyhydramnios, oligohydramnios, intrauterine growth retardation, single umbilical artery, eye defects, holoprosencephaly, omphalocele, and polycystic kidney may contribute to their clinical courses.