The urea cycle in the Rett syndrome.

The in vivo functioning of the urea cycle in the Rett syndrome (RS) was investigated using alanine load test. The test was carried out in girls with RS and their mothers. These results were compared with those on normal females, males and obligate carriers for ornithine carbamoyltransferase deficiency. Post load hyperammonaemia was not seen in any of the RS girls who were not on medication (valproate). Increased orotate excretion was found in some of the RS girls and mothers. The pattern of urinary excretion of orotate in RS girls and their mothers after a standardised alanine load was similar to that found in female carriers of OCT deficiency. This finding can be explained by a mutant OCT, subject to the Lyon effect, and linked to the gene abnormality in RS or by the presence of an abnormal X-linked mitochondrial protein synthesised in cytoplasma and positioned in close proximity to OCT. Such a protein abnormality could also affect mitochondrial functions in other cells, e.g. in the developing brain.