The infant displays growth characteristics of achondroplasia, which is inherited in an autosomal dominant manner.
Achondroplasia, classically known as dwarfism, is the most common cause of disproportionate dwarfism, which can be classified based on the shortening of the limbs: rhizomelic (shortening of the upper arm or thigh), mesomelic (shortening of the forearm or lower leg), or micromelic (shortening of the entire limb). Achondroplasia has an autosomal dominant mode of inheritance, but most cases typically arise due to activating spontaneous mutations in the fibroblast growth factor receptor (FGFR3) resulting in the inhibition of chondrocyte proliferation. Therefore, longitudinal bone growth via endochondral ossification is disrupted. These mutations are associated with increased paternal age.
Pauli reviews achondroplasia and discusses in further detail morphologic features such as shortened limbs, a large head with frontal bossing, and midface protrusion. Infants will be hypotonic with delayed motor milestones. Individuals are of normal intelligence and life span, but infants are at higher risk of death due to spinal cord compression at the craniocervical junction.
Pauli discusses the management of achondroplasia. If increased intracranial pressure does develop, a ventriculoperitoneal shunt may be placed to relieve the pressure. If spinal stenosis is severe, then spinal surgery may be needed to resolve the stenosis. For the development of sleep apnea, several remedies are available such as positive airway pressure, adenotonsillectomy, and tracheostomy. Also, it is recommended that individuals receive social support especially in adolescence.
Illustration A demonstrates the features of achondroplasia. Notice the rhizomelic shortening of the limbs along with the increased head circumference and normal axial skeleton.
Answers 1, 3-5: Achondroplasia is inherited in an autosomal dominant fashion.
Pauli RM. Achondroplasia. 1998 Oct 12 [Updated 2012 Feb 16]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2014. Available from: http://www.ncbi.nlm.nih.gov/books/NBK1152/