Complex sentence: When Genie was 14 months old, a pediatrician examined her after she came down with a fever; although her illness prevented a definitive diagnosis, the doctor said there was a possibility that she was mentally retarded.
Split into simpler sentences: When Genie was 14 months old, she came down with a fever and was taken to a pediatrician. Upon examining her, the doctor said that although her illness prevented a definitive diagnosis there was a possibility that she was mentally retarded.