1. ; Department of Biochemistry, ICBS; Universidade Federal do Rio Grande do Sul; Porto Alegre, Rs
2. Medical Genetics Service; Hospital de Cl[iacute; Porto Alegre, RS
3. ; Faculdade de Medicina de Ribeirão Preto; Ribeirão Preto, SP Brazil
4. ; Department of Pediatrics; University of Colorado School of Medicine, Denver; Colorado USA
5. ; Department of Clinical Chemistry, Metabolic Unit; Vrije Universiteit Medical Center; Amsterdam
6. ; Department of Child Neurology; Vrije Universiteit Medical Center; Amsterdam The Netherlands