22q13.3 deletion syndrome is a well-known syndrome characterized by typical clinical findings including neonatal hypotonia, absent or severely delayed speech, intellectual disability, and other various features, and detection of a heterozygous deletion of chromosome 22q13.3 with the involvement of at least part of SHANK3. It is reported that 10% to 29% of patients with 22q13.3 deletion syndrome present lymphedema. Here, SHANK3 is linked to Down syndrome.