A founder effect can result from the establishment of a new population by individuals from a larger population or bottleneck events. Certain alleles may be found at much higher frequencies because of genetic drift immediately after the founder event. We provide a systematic literature review of the sporadically reported founder effects in hereditary hemorrhagic telangiectasia (HHT). All publications from the ACVRL1, ENG and SMAD4 Mutation Databases and publications searched for terms “hereditary hemorrhagic telangiectasia” and “founder” in PubMed and Scopus, respectively, were extracted. Following duplicate removal, 141 publications were searched for the terms “founder” and “founding” and the etymon “ancest”. Finally, 67 publications between 1992 and 2020 were reviewed. Founder effects were graded upon shared area of ancestry/residence, shared core haplotypes, genealogy and prevalence. Twenty-six ACVRL1 and 12 ENG variants with a potential founder effect were identified. The bigger the cluster of families with a founder mutation, the more remarkable is its influence to the populational ACVRL1/ENG ratio, affecting HHT phenotype. Being aware of founder effects might simplify the diagnosis of HHT by establishing local genetic algorithms. Families sharing a common core haplotype might serve as a basis to study potential second-hits in the etiology of HHT.

Diagnosis of rare bleeding disorders is challenging and there are several differential diagnostics issues. Next-generation sequencing (NGS) is a useful tool to overcome these problems. The aim of this study was to demonstrate the usefulness of molecular genetic investigations by summarizing the diagnostic work on cases with certain bleeding disorders. Here we report only those, in whom NGS was indicated due to uncertainty of diagnosis or if genetic confirmation of initial diagnosis was required. Based on clinical and/or laboratory suspicion of von Willebrand disease (vWD, n = 63), hypo-or dysfibrinogenemia (n = 27), hereditary hemorrhagic telangiectasia (HHT, n = 10) and unexplained activated partial thromboplastin time (APTT) prolongation (n = 1), NGS using Illumina platform was performed. Gene panel covered 14 genes (ACVRL1, ENG, MADH4, GDF2, RASA1, F5, F8, FGA, FGB, FGG, KLKB1, ADAMTS13, GP1BA and VWF) selected on the basis of laboratory results. We identified forty-seven mutations, n = 29 (6 novel) in vWD, n = 4 mutations leading to hemophilia A, n = 10 (2 novel) in fibrinogen disorders, n = 2 novel mutations in HHT phenotype and two mutations (1 novel) leading to prekallikrein deficiency. By reporting well-characterized cases using standardized, advanced laboratory methods we add new pieces of data to the continuously developing “bleeding disorders databases”, which are excellent supports for clinical patient management.

Hereditary hemorrhagic telangiectasia (HHT) is a rare germline vascular malformation syndrome with a prevalence of 1:5000–1:10,000

Introduction: Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant multisystemic vascular disease with a worldwide prevalence of 1 : 5000 – 1 : 10 000. Diagnosis is based on clinical Curacao criteria. Approximately 85% of HHT cases have heterozygous family-specific mutations in the ENG or ACVRL1 genes. Aim: We investigated 23 Hungarian HHT families, established the genetic diagnosis, executed family-screening and confirmed founder effects. Method: Probands were identified by the stratified population screening of the primary attendance area of our institution and from individuals contacting our study group voluntarily. Diagnosis is based on the otorhinolaryngological physical examination completed with characteristic telangiectasis sites, a visceral arteriovenous malformation screening and the sequence analysis of ENG and ACVRL1 genes. The family screening consists of physical examination and genetic screening for the family-specific mutation, followed by the arteriovenous malformation screening in patients with definite/suspected HHT and/or in individuals with the mutation. Results: Sixty-three individuals with family-specific mutations were identified in 22 families, 48 of them with definite and 12 with suspected HHT. Seven ENG and ACVRL1 mutations were detected, respectively; most of these are pathogenic. Three founder mutations were observed. One proband with definite HHT had wild-type alleles in all tested HHT-specific loci. Conclusions: The significance of genetic testing is confirming or excluding HHT in young asymptomatic individuals in families with pathogenic mutations. As ENG and ACVRL1 mutations result in overlapping fenotypes, the genetic testing lacks any prognostic value. The identification of founder effects might simplify the genetic diagnosis of new HHT patients from a given region. Orv Hetil. 2019; 160(18): 710–719.

Hereditary haemorrhagic telangiectasia (HHT; Osler–Weber–Rendu disease) is an autosomal dominant vascular disease characterized by nosebleeds, mucocutaneous telangiectases, visceral arteriovenous malformations (AVM) and a first-degree relative with HHT. Diagnosis is definite if three or four criteria are present. This case report describes a 19-year-old male with incidentally detected polycythaemia and an associated soft-tissue opacity over the left lower lobe on his frontal chest radiogram. He had experienced dyspnoea on exertion since infancy and clubbing at physical examination. Polycythaemia vera, chronic obstructive pulmonary disease, sleep apnoea and cyanotic congenital heart disease were excluded. Chest computed tomography (CT) was initially refused by the patient, but 3 years later he presented with severe epistaxis. Considering the unvarying soft tissue mass and erythrocytosis, an HHT-associated pulmonary AVM (PAVM) was eventually confirmed by chest CT. A pathogenic family-specific ENG c.817-2 A>C mutation was detected in the patient. The large PAVM was successfully treated using AMPLATZER™ vascular plug embolization. A combination of the multisystemic nature of his symptoms, the age-related penetrance of HHT symptoms and insufficient patient compliance delayed the diagnosis of HHT in this current case.