A 12-year-old mentally retarded girl with a large deletion of the long arm of chromosome 21 and congenital hypothyroidism is reported from the Department of Clinical Genetics and Pediatrics, University Hospital, Uppsala, Sweden. Despite the large chromosome deletion, the degree of mental retardation was mild and severe manifestations of Down syndrome were absent. The proximal part of the long arm of chromosome 21 does not include the genes responsible for severe clinical effects seen in Down syndrome. Congenital hypothyroidism in this patient might indicate the importance of genes on chromosome 21 for thyroid function. 
COMMENT. Patients with Down syndrome often suffer from thyroid disorders and congenital hypothyroidism is much more common in DS than in normal individuals. It is likely that the congenital hypothyroidism in the above patient was related to the chromosome 21 abnormality.
The clinical manifestations of partial deletion of chromosome 21 have included mild mental retardation, short stature, obesity, hypotonia, prominent forehead, downslanting palpebral fissures, hyperopia, large/low set ears, high arched palate, prognathism, long/slender hands, short 5th finger, broad feet, large stiff joints, and congenital hypothyroidism.