HRR genes play key roles in restoring the original DNA sequences in cases of double-strand break damages [41,42]; therefore, the loss of function in HRR proteins leads to the impairment of this machinery, i.e., homologous recombination deficiency (HRD), due to the alterations of key genes such as BRCA1/2, RAD51C, RAD51D, and PALB2 [43]. The gene discussed is RAD51D; the disease is hypoparathyroidism-retardation-dysmorphism syndrome.