Laboratory and clinical features of lactate dehydrogenase subunit deficiencies.

Heterozygous subjects with lactate dehydrogenase (LD) subunit deficiencies do not always show a low serum LD activity. Thus, it is necessary to examine the serum and erythrocyte LD isozyme patterns when screening for these conditions. We assessed patients with heterozygotes for H and M subunit deficiency by immunoblotting with anti-H subunit antibody. We could not find any protein or variant proteins in the heterozygous subjects with M subunit deficiency. On the other hand, the existence of variant protein was confirmed in the heterozygous subjects with H subunit deficiency. However, in one patient with homozygous for H subunit deficiency, no H subunit protein was observed. It is suggested that possibly many types of LD subunit deficiency may exist. Only patients with homozygous for M subunit deficiency show common patterns of clinical findings. All patients with LD subunit deficiencies have the risk of misdiagnosis of other clinical conditions from laboratory data because LD release is reduced. Thus it is important to detect them as a latent hereditary symptom poor disorders recognizing in laboratory medicine.