Table I. Genes (loci) contributing to HPE.
| Human gene | (Human locus) | Chromosome | Molecular function |
|---|---|---|---|
| ---- | HPE1 | 21q22.3 | (unknown) |
| SIX3 | HPE2 | 2p21 | Forebrain and eye development |
| SHH | HPE3 | 7q36 | Ventral CNS patterning |
| TGIF | HPE4 | 18p11.3 | Transcriptional repressor including retinoids |
| ZIC2 | HPE5 | 13q32 | Axis formation and dorsal brain development |
| ---- | HPE6 | 2q37.1-q37.3 | (unknown) |
| PTCH1 | HPE7 | 9q22.3 | Receptor for hedgehog ligands |
| ---- | HPE8 | 14q13 | (unknown) |
| GLI2 | HPE9 | 2q14 | Transcription factor mediating hedghog signaling |
| ---- | HPE10 | ---- | (unknown) |
| DISP1 | ---- | 1q42 | Release of hedgehog ligands |
| NODAL | ---- | 10q | TGFβ-like ligand involved in midline and laterality establishment |
| FOXH1 | ---- | 8q24.3 | Transcription factor for NODAL signaling |
Note that not all chromosomal loci implicated in HPE have genes that are considered firmly established as contributory. Furthermore, additional loci will undoubtedly be characterized by comparative hybridization strategies or other methods.