The long-range objective of this project is to clarify the genetic and biochemical sub-structure of the hexosaminidase deficiency diseases, a group of recessively inherited lysosomal storage diseases. Using a coordinated clinical, genetic, and biochemical program we are trying to determine how many subunits (or distinct genetic loci) are required for full hexosaminidase enzyme activity and how can deficiency of one enzyme (hexosaminidase) cause so many different clinical disorders? At least 19 hexosaminidase deficiency diseases are known, 8 of which were discovered in our laboratory. We are studying 5 of these in patients and carriers using a variety of techniques including fractionation of fibroblast or urinary hexosaminidases by isoelectricfocussing; studying the abnormal residual hexosaminidases for abnormal kinetic properties, abnormal lability of the enzyme or other abnormal properties suggesting a mutation affecting the active site, subunit binding, or other enzyme protein function; somatic cell hybridization with Tay-Sachs or Sandhoff fibroblasts to see if genetic complementation occurs; and natural substrate studies. Our preliminary evidence suggests that 5 of these new disorders may be alpha-subunit disorders and 4 may be beta-subunit disorders. One disorder appears to be the result of defective subunit binding. Abnormally heat-labile hexosaminidase has been found in two disorders. Abnormal pI of a hexosaminidase isozyme was found in one disorder. Abnormal substrate specificities were found in one disorder. We propose to extend these studies to all 9 new hexosaminidase disorders and ultimately to all hexosaminidase deficiency diseases. In this way it may be possible to incorporate these disorders into a multiple loci-multiple alleles system as has been done with the hemoglobinopathies. And it may be possible to show for each disorder how the mutation causes a reduction in enzyme activity.
