Trisomy 18 and Trisomy 21 are genetic disorders that involve chromosomal changes. Trisomy 21 is also known as congenital dysmorphism, which means that the patient is extremely mentally retarded and has special features and heart malformations. trisomy 18, also known as Edward’s syndrome, can present with developmental delays, such as abnormally slow growth, or mental retardation and renal disability. There may be difficulty in feeding or breathing, or microcephaly.