Bernard-Soulier in Iceland. Bleeding Symptoms and Platelet Parameters in Patients, Carriers and Controls.
Authors: Onundarson Pall Torfi , Birgisdottir Elisabet R. , Bragadottir Gudrun , Hilmarsdottir Bylgja , Gudmundsdottir Brynja , Vidarsson Brynjar , Magnusson Magnus K. 
Published: April 2020

Bernard Soulier syndrome is a rare platelet disorder characterized by macrothrombocytopenia and absence of platelet aggregation in response to ristocetin due to inherited structural abnormalities in the glycoptein 1B complex. Due to the rarity of this disorder no systematic controlled evaluation has been reported to define the hematological abnormalities and clinical symptoms of these patients. In order to evaluate these findings associated with both Bernard Soulier syndrome and carrier status of glycoprotein 1B-alpha (GP1Bα) mutations we have conducted a nation-wide study in Iceland. All patients with Bernard Soulier syndrome diagnosed in Iceland are referred to the Landspitali University Hospital hemostasis center, a total of twelve patients. Of these, ten were available for the study along with 21 heterozygote carriers (first or second degree relatives) and 25 normal controls. All participating subjects answered a detailed questionnaire on bleeding history and had blood tests, including a complete blood count, coagulation tests, platelet aggregation, PFA-100 closure times, platelet flow cytometry, and DNA analysis to define the underlying GP1Bα mutational status.

A diagnosis of Bernard Soulier syndrome was confirmed by platelet ristocetin aggregation and flow cytometry in all patients. Of these ten patients, seven were homozygous for a specific Icelandic mutation, T283 to C (Cys65 to Arg) in the conserved leucine-rich repeats within the ligand-binding region of platelet GP1Bα. Two patients had compound heterozygosity, Cys65 to Arg and a previously described Swedish mutation (Karlstad mutation), G1584 to A (Trp 498 to Stop) with both mutations in GP1Bα. One patient was compound heterozygous for the Karlstad mutation as well as an uncharacterized mutation. Of the 21 carriers, 14 had the Icelandic mutation and 6 had the Karlstad mutation and one had the uncharacterized mutation. As expected all patients had very significant macrothrombocytopenia with no expression of the GP1B complex on flow cytometry and absolute absence of ristocetin aggretion response. Compared to normal controls, the BS patients reported excessive bleeding manifested by markedly increased bruisability, prolonged small cut bleeding and increased mucosal bleeding (epistaxis, oral cavity, menstruation). Heterozygote carriers also reported moderately increased bruisability compared to normal controls, longer bleeding from small cuts and increased mucosal bleeding (epistaxis, oral cavity). On blood analysis the carriers had significantly lower platelets counts (189 vs. 266 × 109/L, p&lt;0.0001 ) and larger platelets (9.6 fl vs. 7.8 fl, p&lt;0.0001 ) than controls. The PFA-100 closure times (both CT c/epi and CT c/ADP) were markedly prolonged in all patients while carriers and controls had similar normal values.

In this nation-wide study of Bernard Soulier syndrome we have characterized the clinical and hematological symptoms of patients and carriers. As expected the patients have significant clinical mucosal bleeding symptoms and hematological abnormalities. Interestingly we find evidence of mild platelet dysfunction in heterozygote carriers marked by symptoms of increased mucosal bleeding and lower platelet counts as well as larger platelets than controls.