The tyrosinase-deficient Oculocutaneous Albinism (OCA) syndromes are a group of serious autosomal recessive genetic disorders characterized principally by decreased pigment biosynthesis, resulting from deficient activity of tyrosinase in melanocytes. Using previously-cloned mouse tyrosinase cDNA probes, we plan to clone and sequence the normal human tyrosinase gene. We also plan to characterize molecular lesions of the tyrosinase gene in patients with the tyrosinase-deficient OCAs, and to determine the relative frequencies and distribution of these mutations in the population. This will be approached by identifying restriction fragment length polymorphisms (RFLPs) linked to the tyrosinase gene, and determining the RFLP haplotypes associated with defective tyrosinase genes in patients with tyrosinase-deficient OCAs. Tyrosinase gene deletions will be identified by Southern blot hybridization analysis of patient DNAs. Single-base mutations causing OCA will be identified in most cases by rapid screening of genomic DNA to localize base substitutions, followed by amplification of appropriate gene segments by polymerase chain reaction and DNA sequence analysis. In a minority of cases, cloning and DNA sequence analysis of the abnormal gene may be necessary. The functional effects of selected mutations will be assayed by inserting candidate base substitutions into the normal human tyrosinase gene by oligonucleotide-directed mutagenesis, followed by transient introduction of the mutant gene into He L cells. Finally, we plan to apply the results of these analyses to the development of the improved carrier detection and prenatal diagnoses of the OCAs. This approach has already proved very useful in the analysis and management of many other human genetic diseases, and should greatly enhance the genetic counseling and clinical options available to families at risk for OCA.
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