Apparent 'dominant' and 'recessive' inheritance of von Willebrand's disease within the same kindreds. Possible biochemical mechanisms

The molecular biology of von Willebrand disease

von Willebrand disease (VWD) is a common autosomally inherited bleeding disorder associated with mucosal or trauma-related bleeding in affected individuals. VWD results from either a quantitative or qualitative deficiency of von Willebrand factor (VWF)--a glycoprotein with essential roles in primary haemostasis and as a carrier of coagulation factor VIII (FVIII) in the circulation. In recent years the identification of mutations in the VWF gene in patients with VWD has improved our understanding of the structure and function of the VWF protein, and has illustrated the importance of specific regions of VWF for its interaction with other components of the vasculature. The underlying genetic lesions and associated molecular pathology have been identified in many cases of type 2A, type 2B, type 2M, type 2N and type 3 VWD. However in the most common variant, type 1 VWD, the causative molecular defect is unknown in the large majority of cases. In the absence of an understanding of the molecular pathology underlying type 1 VWD, precise diagnosis and classification of this common disorder remains problematic.

Congenital von Willebrand disease type 3: clinical manifestations, pathophysiology and molecular biology

von Willebrand disease type 3 is the most severe form of this condition. Patients present with a moderate-to-severe bleeding tendency. The plasma von Willebrand factor level in these patients is very low or undetectable. Although rare, von Willebrand disease type 3 is of major interest because of its severe clinical presentation, the need for replacement therapy and the risk of occurrence of alloantibodies after the infusion of plasma concentrates. The inheritance of type 3 disease is typically autosomal recessive. The parents are often consanguineous, although compound heterozygous inheritance does occur. The molecular basis of von Willebrand disease type 3 has recently been studied in detail, several molecular defects being identified. This chapter will focus on the clinical and molecular aspects of type 3 von Willebrand disease.

Inheritance of von Willebrand's disease in a colony of Doberman Pinschers

OBJECTIVE

To determine the mode of inheritance of von Willebrand's disease (vWD) and perform linkage analysis between vWD and coat color or narcolepsy in a colony of Doberman Pinschers.

ANIMALS

159 Doberman Pinschers.

PROCEDURE

von Willebrand factor antigen (vWF:Ag) concentration was measured by use of ELISA, and results were used to classify dogs as having low (< 20%), intermediate (20 to 65%), or high (> 65%) vWF:Ag concentration, compared with results of analysis of standard pooled plasma. Buccal bleeding time was measured, and mode of inheritance of vWD was assessed by pedigree analysis.

RESULTS

von Willebrand's disease was transmitted as a single autosomal gene defect. Results suggested that 27.04% of dogs were homozygous for vWD, 62.26% were heterozygous, and 10.69% did not have the defect. Most homozygous and some heterozygous dogs had prolonged bleeding times. Dogs with diluted coat colors (blue and fawn) were significantly overrepresented in the homozygous group, compared with black and red dogs, but a significant link between vWD and coat color was not detected.

CONCLUSIONS AND CLINICAL RELEVANCE

von Willebrand's disease is transmitted as an autosomal dominant trait with variable penetrance; most dogs in this colony (89.3%) were carriers of vWD. Homozygosity for vWD is not likely to be lethal. Some heterozygous dogs have prolonged bleeding times. An association between diluted coat colors and vWD may exist.

Recessive inheritance of von Willebrand's disease type I

The inheritance of type I von Willebrand's disease is thought to be autosomally dominant. The laboratory profile may, however, vary between affected people, even within a single family. There is also a large variation in the severity of clinical symptoms. To see if there is an association between the von Willebrand factor genotype, the laboratory profile, and the severity of the clinical symptoms we did a genetic analysis of four families with type I von Willebrand's disease. The proband of each family proved to be a compound heterozygote for defects in the von Willebrand factor gene. Simple heterozygotes in these families were either symptomless or only mildly affected. One of the identified mutations, which was shared by the probands of three of the four families, may have a carrier prevalence of 1:50 in the general population. These results suggest that the inheritance of von Willebrand's disease is often recessive rather than dominant and so have important implications for diagnosis and genetic counselling.

A relatively high frequency of severe (type III) von Willebrand's disease in Israel

Sixty patients with von Willebrand's disease belonging to 34 unrelated families were classified into the various types of the disease by analysis of the multimer patterns of von Willebrand factor. Type I disease was observed in 62% of the families, a finding similar to the recently published British and Swedish series of patients. Type III (severe) von Willebrand's disease was observed more frequently in the Israeli group (29%) than in the other two series. Of the 16 patients with type III disease eight were Arabs living in Israel, the West Bank and the Gaza Strip (total population about 1.5 X 10(6). Thus, it appears that the frequency of type III disease is very high among Arabs (5.3/10(6]. Sibship analysis of all families affected by the type III mutant gene was compatible with an autosomal recessive mode of inheritance. An attempt was made to define carriers of type III disease and to distinguish them from type I patients and from healthy subjects. In 15 obligate carriers of type III disease mean levels of factor VIII clotting activity, of von Willebrand factor and of ristocetin cofactor were significantly higher than the corresponding mean values observed in 31 symptomatic and 12 asymptomatic type I patients, and in turn significantly lower than the corresponding mean values observed in 30 healthy subjects. Ristocetin cofactor was the best criterion for discrimination among carriers of type III disease, normal subjects and type I patients.