Objective:
To diagnose the carriers and noncarriers in a family affected with Norrie disease based on molecular analysis.
Design:
Family members from three generations, including one affected patient, two obligate carriers, one carrier identified with linkage analysis, one noncarrier identified with linkage analysis, and one female family member with indeterminate carrier status, were examined clinically and electrophysiologically. Linkage analysis had previously failed to determine the carrier status of one female family member in the third generation. Blood samples were screened for mutations in the Norrie disease gene with single-strand conformation polymorphism analysis. The mutation was characterized by dideoxy-termination sequencing.
Results:
Ophthalmoscopy and electroretinographic examination failed to detect the carrier state. The affected individuals and carriers in this family were found to have a transition from thymidine to cytosine in the first nucleotide of codon 39 of the Norrie disease gene, causing a cysteine-to-arginine mutation. Single-strand conformation polymorphism analysis identified a patient of indeterminate status (by linkage) to be a noncarrier of Norrie disease.
Conclusion:
Ophthalmoscopy and electroretinography could not identify carriers of this Norrie disease mutation. Single-strand conformation polymorphism analysis was more sensitive and specific than linkage analysis in identifying carriers in this family.