The occurrence of holoprosencephaly can often be linked to a genetic cause or risk factor.
Hereditary syndromes:
(1) Smith-Lemli-Opitz syndrome
(2) Holoprosencephaly-Polydactyly Syndrome (Pseudo-Trisomy 13)
(3) trisomy 18
(4) triploidy
(5) other
Deletions or mutations in:
(1) sonic hedgehog (SHH, on 7q36)
(2) ZIC2 (on 13q32)
(3) SIX3 (on 2p21)
(4) TGIF (on 18p11.3)
(5) GLI2 (on 2q14)
(6) NODAL (on 10q22.1)
(7) FGF8 (on 10q24)
Risk factors:
(1) maternal diabetes
(2) failure to take folic acid before and during the pregnancy
(3) multiple gestations
(4) exposure to a teratogen during the first month postconception (at least in animals)
