Immunodeficiency in methylmalonic acidaemia.

Three Chinese infants with methylmalonic acidaemia were described. They presented in the neonatal period with recurrent episodes of poor feeding, lethargy, apnoea and severe acidosis. The diagnosis was established by increased methylmalonic acid concentration in the plasma and/or urine. Pancytopenia was a prominent feature in all three patients. Only patient three had assessment of lymphocyte subsets and it showed diminished population of B-lymphocytes and a reversed CD4/CD8 ratio. All three patients were unresponsive to vitamin B12. They experienced severe infections including Gram-negative septicaemia, candidiasis and Pneumocystis carinii pneumonia which caused their deaths. Patients with this disease should be regarded as having severe immunodeficiency, and in addition to optimal metabolic control, they should be treated aggressively for any suspected infective episodes.