RT Book, Section A1 Bianchi, Diana W. A1 Crombleholme, Timothy M. A1 D'Alton, Mary E. A1 Malone, Fergal D. SR Print(0) ID 1106396444 T1 Holoprosencephaly T2 Fetology: Diagnosis and Management of the Fetal Patient, 2e YR 2015 FD 2015 PB McGraw-Hill Education PP New York, NY SN 978-0-07-144201-5 LK obgyn.mhmedical.com/content.aspx?aid=1106396444 RD 2024/03/29 AB Key PointsA complex brain malformation characterized by the forebrain failing to cleave into two hemispheres, a process that is usually completed by 5 weeks.Four subtypes exist, listed in order of decreasing severity: alobar, semilobar, lobar, and middle hemispheric variant.Incidence is approximately 1 in 8000 second trimester pregnancies.Approximately 40% of cases have a chromosome abnormality. Of these 75% are due to trisomy 13.Maternal diabetes increases the risk of holoprosencephaly by 200-fold.Management of pregnancy should include fetal karyotype, DNA mutation testing, and consideration of fetal MRI. A detailed family history should be obtained.Mutations in eight different genes are associated with holoprosencephaly (SHH, PTCH, SIX3, SL12, ZIC2, TGIF, TDGF1, and FAST1).If chromosome abnormalities and craniofacial anomalies are absent, long-term survival is possible.