NHEJ1 and Severe short stature: Based on physiological and genetic characteristics, four distinct types of dwarfism in chickens have been identified: sex-linked dwarfism, which has been well-studied and is caused by mutations in the growth hormone receptor gene (GHR) [8,9]; autosomal dwarfism, which is caused by a nonsense mutation in the transmembrane protein 263 gene (TMEM263) [10]; the bantam phenotype, associated with the HMGA2 gene on chromosome 1 [11]; and creeper dwarfism due to a creeper allele described as a 25 kb deletion containing the IHH and non-homologous end-joining factor 1 (NHEJ1) genes [12,13].