Component of the shelterin complex (telosome) that is involved in the regulation of telomere length and protection. Shelterin associates with arrays of double-stranded TTAGGG repeats added by telomerase and protects chromosome ends. Without its protective activity, telomeres are no longer hidden from the DNA damage surveillance and chromosome ends are inappropriately processed by DNA repair pathways. Promotes binding of POT1 to single-stranded telomeric DNA. Modulates the inhibitory effects of POT1 on telomere elongation. The ACD-POT1 heterodimer enhances telomere elongation by recruiting telomerase to telomeres and increasing its processivity (By similarity). May play a role in organogenesis (PubMed:15537664). Component of the shelterin complex (telosome) composed of TERF1, TERF2, TINF2, TERF2IP ACD and POT1. Forms heterodimers with POT1. Identified in a complex with POT1 and single-stranded telomeric DNA. Interacts with STN1 and TINF2. Ubiquitous. Expressed from 7 dpc to 18 dpc throughout development. Defects in Acd are the cause of adrenocortical dysplasia (ACD). ACD is a spontaneous autosomal recessive mouse mutant resulting from spontaneous splicing mutation of acd. ACD mice are characterized by developmental defects in organs derived from the urogenital ridge, reduced survival, poor growth, skin hyperpigmentation and adrenal insufficiency. Forty percent of the mutants died within 24 hours. Analysis of 14.5 dpc to 17.5 dpc embryos revealed reduced formation of caudal structure as well as limb defects. Adrenocortical dysplasia mouse was initially reported as a model of human congenital adrenal hypoplasia (AHC).