Partial monosomy 18p and 21q due to a paternal reciprocal translocation leading to holoprosencephaly.

Here we report a patient with holoprosencephaly (HPE) associated with 45, XY,der(18)t(18;21)(p11.2;q21.3),-21 derived from a paternal balanced reciprocal translocation. Array comparative genomic hybridization analysis revealed 18p11.32-p11.21 and 21q11.2-q21.3 deletions. So far, nine cases of monosomy 18p with an unbalanced translocation (18;21) have been reported, four of which presented with HPE. Our case provides a detailed long-term clinical course and helps us to better understand these rare genetic events.