Detection of inborn errors of metabolism

Human fibroblasts, cultured on glass microscope slides, were examined autoradiographically for their ability to incorporate radioactivity from Na‐propionate‐l‐ 14C into TCA‐insoluble cell material. Cells from patients with propionic acidemia (PA) and methylmalonic acidemia (MMA), both B12‐sensitive and B12‐insensitive, incorporate little or no radioactivity and thus can be readily distinguished from cells of a number of individuals with no defects in this pathway. Incorporation in cells from non‐MMA individuals is significantly enhanced in a basal medium by high levels of glucose. This procedure should be readily adaptable for use in screening for disorders of propionate metabolism, particularly before birth.