BRCA1 and BRCA2 are both tumor-suppressor genes involved in a homologues recombination (HR) system which has a main role in DNA damage repair before cell replication; in fact, BRCA1 and BRCA2 mutations are commonly associated with Homologous Recombination Deficiency (HRD), including other genes indirectly involved in the pathway such as ARID1A, ATM, p53 and PTEN [36,37]. The gene discussed is ARID1A; the disease is hypoparathyroidism-retardation-dysmorphism syndrome.