Survivorship of Individuals With Double Heterozygosity for Achondroplasia and Type 2 Collagenopathy.

Historically, double heterozygosity, or a diagnosis of two separate, dominant genetic conditions, was often thought to be lethal in individuals with autosomal dominant skeletal dysplasias. In previously published studies of individuals with dual dysplasia diagnoses of achondroplasia and type 2 collagenopathy, infants died of respiratory complications. These reports have likely guided perinatal counseling and management recommendations provided to expectant families with these specific dual-dysplasia diagnoses. We present two clinical reports of unrelated children with both achondroplasia and type 2 collagenopathy who received multidisciplinary care and life-sustaining medical interventions including a tracheostomy, gastrostomy tube, and neurosurgical management. With these interventions, these individuals have outlived the previously reported life expectancy, and their parents report a good quality of life.