Exclusion of haemophilia B in male fetus by chorionic villus biopsy

Manic depressive illness not linked to factor IX region in an independent series of pedigrees

We studied seven informative kindreds segregating for manic depressive illness (MDI), consistent with X-chromosome transmission of the trait (families do not show affective disease in both a father and a son), using markers mapped to the region of Xq27-Xq28. The lod scores were consistently below -2 in the region extending from about 10 cM centromeric from the Factor IX locus (F9) to the colorblindness region. This study does not replicate previous reports of linkage of MDI to Factor IX (Xq27) and colorblindness region (Xq28) chromosomal markers in other kindreds.

Hemophilia B (Christmas disease) variants and carrier detection analyzed by DNA probes

We have used two strategies to study 14 hemophilia B families from 11 kindreds for possible carrier detection and prenatal diagnosis. First, we sequentially used the Factor IX probes (sequentially with restriction enzymes Taq I, Xmn I, and Dde I), and the linked probes p45h (Taq I), p45d (Pst I), and 52a (Taq I) for restriction fragment length polymorphism (RFLP) analysis. Second, we searched for useful variant Taq I digestion fragments using the Factor IX complementary DNA. Two separate new Taq I variants in exon VIII were identified. Using both strategies, 11 of 14 families (from 9 of 11 kindreds) were informative for further studies. In five kindreds studied in detail, the carrier status of all 11 at risk females was determined and prenatal diagnosis could be offered to the offsprings of each of the six carriers identified. Thus, in this study, we have identified a higher proportion of informative families than has previously been reported.

Reproductive choices in hemophilic men and carriers

We have examined reproduction patterns in hemophilic men and carrier women seen at a hemophilia treatment center. The study group included 309 patients with hemophilia A or B: 194 adults and 115 children from 246 pedigrees; 93% of affected men and 96% of parents of affected children had received genetic counseling. In the collected pedigrees, 65% of affected males were born to women with family history of hemophilia. An additional 23% of mothers were later shown to be carriers. Fewer than 12% of cases could be due to a new mutation in the child. Among 209 hemophilia A carrier tests, 95% of obligate carriers were detectable, 87% of mothers of sporadic cases, 53% of sisters of hemophiliacs, and 24% of other relatives had a high risk of carriership. Of 49 high-risk women seen during or prior to pregnancy, one-half elected prenatal diagnosis. Amniocentesis was performed in 24 cases and 8 were referred for fetoscopy, resulting in 18 normal offspring. Among 25 pregnancies not tested, 14 continued and produced 3 affected males and 11 normal offspring. Of hemophilic men over age 25, 66% have married and 41% (62% of those married) have had children. These observations will serve as a baseline for assessing any change in reproductive patterns occurring with the introduction of new genetic techniques.

Genetic analysis of the fragile-X mental retardation syndrome with two flanking polymorphic DNA markers

The fragile-X mental retardation syndrome, one of the most prevalent chromosome X-linked diseases (approximately equal to 1 of 2000 newborn males), is characterized by the presence in affected males and in a portion of carrier females of a fragile site at chromosomes band Xq27. We have performed a linkage analysis in 16 families between the locus for the fragile-X syndrome, FRAXQ27, and two polymorphic DNA markers that correspond to the anonymous probe St14 and to the coagulation factor IX gene F9. Our results indicate that the order of loci is centromere-F9-FRAXQ27-St14-Xqter. The estimate of the recombination fraction for the linkage F9-FRAXQ27 is 0.12 (90% confidence limits: 0.044-0.225) and 0.10 for FRAXQ27-St14 (90% confidence limits: 0.040-0.185). Recombination between St14 and F9 does not appear to be significantly different in normal and fragile-X families. The two flanking probes were used for diagnosis of the carrier state and for detection of transmission of the disease through phenotypically normal males. They should also allow first-trimester diagnosis with a reliability of about 98% in 40% of the families. Used in conjunction with the cytogenetic analysis, the segregation studies with both probes should improve the genetic counseling for the fragile-X syndrome and should be useful for the formal genetic analysis of this unique disease.

A new MspI restriction fragment length polymorphism in the hemophilia B locus

Using a partial cDNA probe for human coagulation factor IX, we have detected a new restriction fragment length polymorphism in human DNA digested with MspI. The frequency of the minor allele is 0.20 +/- 0.05 and average heterozygosity is about 0.32. The MspI RFLP is in strong linkage disequilibrium with the TaqI RFLP previously described, but should nevertheless be useful in segregation analysis in case of homozygosity for the TaqI minor allele.