A 2-year old girl is taken to a pediatrician because she has developed a rash and seems unusually unsteady when she tries to walk. Physical examination demonstrates a diffuse rash on body parts exposed to sun. Also noted are short stature, possible mental retardation, and ataxia. Screening studies demonstrate increased total amino acids in the urine. Which of the following is most likely diagnosis?
A. Alkaptonuria
B. Cystinuria
C. Hartnup disease
D. Fanconi syndrome
E. Phenylketonuria