LAUSR

Platelets play a crucial role in primary haemostasis as they adhere at the site of vascular breachs, aggregate and initiate clot formation [1]. Inherited platelet function disorders (IPFD) comprise a rare and heterogeneous group of diseases characterised by abnormalities in the primary haemostatic capacity of platelets [2, 3]. The causes of IPFD are multiple and diverse and can be classified in: (i) non-syndromic inherited platelet disorders; or (ii) congenital syndromic diseases such as Hermansky-Pudlak, Chediak-Higashi, or Leukocyte Adhesion Deficiency-III [4]. A rapid and accurate diagnosis of the syndromic forms is particularly important to initiate correct management that may help to prevent disease complications. However, target-organ damage associated to platelet dysfunction could be sometimes subclinical, leading to diagnostic delay of the disease [5, 6]. Platelet dysfunction has been also described in Noonan syndrome (NS). We here report the detailed clinical description of an adult patient with atypical late diagnosis of NS revealed by abnormal platelet function studies, highlighting the challenges in recognizing subclinical phenotype and the increasing role of molecular diagnosis. The propositus is a 58 year-old man who was referred to us for a lifelong history of bleeding. He did not report any spontaneous bleeding events, but presented bleeding complications after surgeries. He had undergone surgical correction for ectopic testis and repeated surgical excision for lymphangiomas with bleeding complications, but did not require any revision surgery. Nevertheless, he required a red blood cells transfusion during a sigmoidectomy. He also presented gastrointestinal bleeding when he was taking rivaroxaban for atrial fibrillation. Laboratory testing revealed normal white blood count, hemoglobin and the number/morphology of his platelets were normal. Coagulation screening tests such as prothrombin time and activated partial thromboplastin time were all within reference ranges. Von Willebrand factor assays (antigen, ristocetin cofactor and ratios) and factor XIII activity were normal. Platelet screening demonstrated a reduced maximal aggregation in response to arachidonic acid, U46619 TPα receptor agonist and low doses of thrombin receptor–activating peptide-14 (TRAP-14), whereas * Mathieu Fiore [email protected]