[Ring chromosome 21 as a cause of developmental disorder. A case report from the practice of child psychiatry].

Ring chromosome 21 is a very rare chromosomal abnormality known to cause a great variety of clinical findings. Persons with ring chromosome 21 can be intellectually and phenotypically normal, but this abnormality is found more often in persons with dysmorphic features, malformations and mental retardation. Ring chromosome 21 is also encountered as the only chromosomal abnormality in individuals with Down syndrome. We describe a four year old girl with ring chromosome 21 (karyotype 46,XX/46,XX,-21, +r(21)), who was examined in a department of child psychiatry because of delayed development. The child had serious speech and language problems, slightly dysmorphic features and bilateral hip-joint dysplasia.