Trisomy 13 mosaicism

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.

The clinical and cytogenetic findings of two new cases of trisomy 13 mosaicism are described.

The importance of prenatal diagnosis, clinical findings, and interdisciplinary medical evaluation is highlighted, as well as an appropriate genetic counseling.