AbstractCiliopathies are genetic syndromes that link osteochondrodysplasias to dysfunction of primary cilia. Primary cilia extend from the surface of bone and cartilage cells, to receive extracellular cues and mediate signaling pathways. Mutations in several genes that encode components of the intraflagellar transport-A ciliary protein complex have been identified in skeletal ciliopathies, includingTHM1. Here, we report a role for genetic interaction betweenThm1and its paralog,Thm2,in skeletogenesis. THM2 localizes to the ciliary axoneme, but unlike its paralog,Thm2deficiency does not affect ciliogenesis andThm2-null mice survive into adulthood. Since paralogs often have redundant functions, we crossed aThm1null (aln) allele into theThm2colony. After 5 generations of backcrossing the colony onto a C57BL6/J background, we observed that by postnatal day 14,Thm2-/-; Thm1aln/+mice are smaller than control littermates.Thm2-/-; Thm1aln/+mice exhibit shortened long bones, narrow ribcage, shortened cranium and mandibular defects. Mutant mice also show aberrant architecture of the tibial growth plate, with an expanded proliferation zone and diminished hypertrophic zone, indicating impaired chondrocyte differentiation. Using microcomputed tomography,Thm2-/-; Thm1aln/+tibia were revealed to have reduced cortical and trabecular bone mineral density. Deletion of one allele ofGli2, a major transcriptional activator of the Hedgehog (Hh) pathway, exacerbated the small phenotype ofThm2-/-; Thm1aln/+mice and caused small stature inThm2-null mice. Together, these data revealThm2as a novel locus that sensitizes to Hh signaling in skeletal development. Further,Thm2-/-; Thm1aln/+mice present a new postnatal ciliopathy model of osteochondrodysplasia.