disease arises from structure disease arises from alteration in structure chromosome 21 (Human) tetrasomy 21 https://rarediseases.info.nih.gov/diseases/12480/tetrasomy-21 https://www.malacards.org/card/tetrasomy_21 SCTID:764690001 MEDGEN:1640242 GARD:0012480 Orphanet:96055 Isochromosome 21 tetrasomy type 21 UMLS:C4707057 Tetrasomy 21 is an extremely rare autosomal anomaly resulting from the presence of 4 copies of chromosome 21, characterized by features of trisomy 21 including developmental delay/intellectual disability, muscular hypotonia, short neck with redundant skin, brachycephaly, microcephaly, flat face, epicanthus, upslanted palpebral fissures, small ears, protruding tongue, single transverse palmar crease, brachydactyly, hypoplastic iliac wings, together with additional features such as prematurity, intrauterine growth retardation, high and broad forehead, hypertelorism. Haematological malignancies are also associated and may occur earlier than in trisomy 21. MONDO:0019864 icd11.foundation:1246904243 tetrasomy chromosome 21 disorder