Trisomy 13 is a chromosomal anomaly caused by the presence of an extra chromosome 13 and is characterized by brain malformations (holoprosencephaly), facial dysmorphism, ocular anomalies, postaxial polydactyly, visceral malformations (cardiopathy) and severe psychomotor retardation.

Partial absence of a free limb (excluding girdle). It can refer to the proximal, middle or distal segment of the upper or lower limb. The deficiency may be transverse or longitudinal. Thus, meromelia is a lack of a part, but not all, of one or more limbs with the presence of a hand or foot.