Trisomy 13 mosaicism.

Background: Trisomy 13 is a chromosomal alteration with an incidence of 1 in 10,000 to 20,000 births. It can occur completely, partially or in mosaicism; the latter occurs when a percentage of cells are trisomic for chromosome 13, while the rest are euploid in an individual and corresponds to only 5% of all cases. Patients with trisomy 13 present a wide variable expressivity, ranging from severe malformations with early death (phenotype similar to the complete form and more frequent), to normal development and few dysmorphic findings. Case reports: The clinical and cytogenetic findings of two new cases of trisomy 13 mosaicism are described. Conclusions: The importance of prenatal diagnosis, clinical findings, and interdisciplinary medical evaluation is highlighted, as well as an appropriate genetic counseling.