Treatments for rare diseases: molybdenum cofactor defi ciency

report on the follow-up of a cohort of infants with molybdenum cofactor defi ciency (MoCD), some of whom benefi ted greatly from a novel therapy. A very rare metabolic disorder is perhaps an unlikely subject for a general medical journal, but new treatments for rare metabolic diseases have problems in common that need much thought. MoCD causes loss of function of the enzyme sulphite oxidase, and is clinically characterised by severe and progressive neurological damage and intractable seizures; symptoms are usually apparent within the fi rst hours or days of life. 2