A mutation in XRCC4 identified by exome sequencing suggested this gene as a candidate disease‐causing mutation in a patient with primordial dwarfism.68 Most recently, XRCC4 mutations were identified within five families in patients with microcephalic primordial dwarfism.69 The alterations found, substantially decrease XRCC4 protein levels leading to reduced cellular ligase IV activity and ionizing radiation‐induced DNA double‐strand break repair defects. This evidence concerns the gene XRCC4 and isolated growth hormone deficiency type IA.