CHARACTERIZATION OF THE FACTOR-VIII DEFECT IN 147 PATIENTS WITH SPORADIC HEMOPHILIA-A - FAMILY STUDIES INDICATE A MUTATION TYPE-DEPENDENT SEX-RATIO OF MUTATION FREQUENCIES

The clinical manifestation of hemophilia A is caused by a wide range o f different mutations. In this study the factor VIII genes of 147 seve re hemophilia A patients-all exclusively from sporadic families-were s creened for mutations by use of the complete panel of modem DNA techni ques. The pathogenous defect could be characterized in 126 patients (8 5.7%). Fifty-five patients (37.4%) showed a F8A-gene inversion, 47 (32 .0%) a point mutation, 14 (9.5%) a small deletion, 8 (5.4%) a large de letion, and 2 (1.4%) a small insertion. Further, four (2.7%) mutations were localized but could not be sequenced yet. No mutation could be i dentified in 17 patients (11.6%). Sixteen (10.9%) of the identified mu tations occurred in the B domain. Four of these were located in an ade nosine nucleotide stretch at codon 1192, indicating a mutation hotspot . Somatic mosaicisms were detected in 3 (3.9%) of 76 patients' mothers , comprising 3 of 16 de novo mutations in the patients' mothers. Inves tigation of family relatives allowed detection of a de novo mutation i n 16 of 76 two-generation and 28 of 34 three-generation families. On t he basis of these data, the male:female ratio of mutation frequencies (k) was estimated as k = 3.6. By use of the quotients of mutation orig in in maternal grandfather to patient's mother or to maternal grandmot her, k was directly estimated as k = 15 and k = 7.5, respectively. Con sidering each mutation type separately, we revealed a mutation type-sp ecific sex ratio of mutation frequencies. Point mutations showed a 5-t o-10-fold-higher and inversions a >10-fold-higher mutation rate in mal e germ cells, whereas deletions showed a >5-fold-higher mutation rate in female germ cells. Consequently, and in accordance with the data of other diseases like Duchenne muscular dystrophy, our results indicate that at least for X-chromosomal disorders the male:female mutation ra te of a disease is determined by its proportion of the different mutat ion types.