Cosegregation of intragenic markers with a novel mutation that causes Crigler-Najjar syndrome type I: Implication in carrier detection and prenatal diagnosis

Crigler-Najjar syndrome type 1 (CN-1) is a familial disorder characterized by severe unconjugated hyperbilirubinemia and jaundice and leads to kernicterus, neurological damage, and eventual death unless treated with liver transplantation. Previous reports identified mutations in the UGT1 gene complex to be the cause of the disease. The total absence of all phenol/bilirubin UGT proteins and their activities in liver homogenate of a CN-1 patient was determined by enzymological and immunochemical analysis. A novel homozygous nonsense mutation (CGA→TGA) was identified in the patient by the combined techniques of PCR and direct sequencing. This mutation was located in exon 3 of the constant region in the gene complex which is common to all phenol and bilirubin UGTs. The segregation of the mutation in the patient's family was analyzed and confirmed the recessive nature of the disease. Newly developed intragenic polymorphic probes (UGT1*4 and UGT-Const) were used on Southern blots of MspI-digested genomic DNA of the patient and his family. The segregation of individual alleles within the family was observed from haplotypes generated. Comparison of the segregation of haplotypes with the mutation for the patient and his family revealed the allele identified by the A1-B1-C2 haplotype to be carrying the mutation. The risk of recombination occurring is negligible, because of the intragenic nature of the probes. This study demonstrates the potential usefulness of these probes in carrier detection and prenatal/presymptomatic diagnosis.