Phenotypes associated with the disease odontoid hypoplasia (OMIM:613628):
- Atlantoaxial instability (HP:0003467): Abnormally increased movement at the junction between the first cervical (atlas) and the second cervical (axis) vertebrae as a result of either a bony or ligamentous anomaly. Evidence: TAS. (OMIM:613628)
- Hypoplasia of the odontoid process (HP:0003311): Developmental hypoplasia of the dens of the axis. Evidence: TAS. (OMIM:613628)
- Cervical instability (HP:0008462). Evidence: TAS. (OMIM:613628)
- Dystopic os odontoideum (HP:0040143): Os odontoideum is classified into two anatomic types (orthotopic and dystopic). Os odontoideum is defined as an ossicle that consists of smooth and separate caudal portions of the odontoid process. With orthotopic os odontoideum, the ossicle moves with the anterior arch of the atlas, while the dystopic type consists of an ossicle near the basion, or one that is fused with the clivus. Evidence: TAS. (OMIM:613628)
- Autosomal dominant inheritance (HP:0000006): A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in heterozygotes. In the context of medical genetics, an autosomal dominant disorder is caused when a single copy of the mutant allele is present. Males and females are affected equally, and can both transmit the disorder with a risk of 50% for each child of inheriting the mutant allele. Evidence: TAS. (OMIM:613628)