Communicated by Garry R. Cutting
DNA sequence analysis of the second SSCP variant revealed a TรA transversion at position 31,167, which results in a predicted phenylalanine to isoleucine missense mutation at codon 349. No other abnormalities in the factor IX gene were identified in either patient. The latter mutation co-segregates with the affected members of the family who have moderately severe CRM + disease with about 1% enzyme activity.
Discussion
Prenatal prediction of fetal genotype may be accomplished in multiple ways, including direct sequencing, creation/destruction of restriction sites by known mutations, oligonucleotide hybridization, and amplification-refractory mutation detection (ARMS). This report details the utility of using the SSCP variant itself when established as either the molecular basis of the disease, or as an intragenic marker.
The F349I variant noted in the second family has not previously been described. The phenylalanine residue at codon 349 is conserved within the catalytic domains of the related coagulation factors VII, IX, X and prothrombin (although not protein C) in humans (Long, 1986). Further, it is conserved within the factor IX protein in humans, sheep, cows, dogs, and mice (Sarkar et al., 1990). 31,167TรA creates a new Mbol restriction site that was used to screen 99 unrelated X chromosomes. No other F349I alleles were detected (data not shown). Strong protein