Prenatal diagnosis of the Dandy-Walker malformation and ventriculomegaly associated with partial trisomy 9p and distal 12p deletion.

OBJECTIVES

To present the prenatal diagnosis and perinatal findings of partial trisomy 9p and distal 12p deletion.

METHODS AND RESULTS

Amniocentesis was performed at 17 gestational weeks due to a balanced reciprocal translocation t(9;12)(p11.2;p13.3) in the mother. The father's karyotype was normal. The family had a 5-year-old daughter with a Dandy-Walker malformation and a trisomy 9p syndrome. Cytogenetic analysis of the cultured amniotic fluid cells revealed a 46,XY,der(12)t(9;12)(p11.2;p13.3)mat karyotype with partial monosomy 12p(12pter-->p13.3) and partial trisomy 9p(9pter-->p11.2). Sonographic examination of the fetal brain and skull showed bilateral ventriculomegaly, brachycephaly and a Dandy-Walker malformation with an enlarged cisterna magna and absence of the cerebellar vermis. The pregnancy was terminated subsequently. At autopsy, the proband manifested agenesis of the cerebellar vermis and a typical trisomy 9p phenotype.

CONCLUSION

Fetuses with partial trisomy 9p(9pter-->p11.2) may present a Dandy-Walker malformation and ventriculomegaly on prenatal ultrasound in the second trimester. A dosage effect of genes located on 9pter-->p11.2 may be associated with the abnormal development of the central nervous system in patients with partial or complete trisomy 9.