Syndrome, Patau: Trisomy 13 syndrome or three chromosome number 13s instead of the normal two. Children with this condition have multiple malformations and mental retardation due to an extra chromosome #13 Named after the late Klaus Patau who described the extra chromosome in 1960. This is trisomy 13 syndrome. There are three rather than the normal two chromosomes #13. Children with this syndrome have multiple malformations and mental retardation due to the extra chromosome #13. The malformations commonly include scalp defects, hemangiomas (blood vessel malformations) of the face and nape of the neck, cleft lip and palate, malformations of the heart and abdominal organs, and flexed fingers with extra digits. The mental retardation is profound. The IQ is untestably low. The majority of trisomy 13 babies die soon after birth or in infancy. Named after the late Klaus Patau who discovered the extra chromosome in 1960.