Founder Effects in Hereditary Hemorrhagic Telangiectasia.

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.

The Stratified Population Screening of Hereditary Hemorrhagic Telangiectasia.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant multisystemic vascular disease with a wordwide prevalence of 1:5000-1:10000. We introduce our algorithm for the stratified population screening of HHT. Probands are selected from the consecutive hospital database review for HHT (I7800) and recurrent epistaxis (R0400) and the review of patient records referred by family practicioners. A proportion of probands might be de novo diagnosed with HHT in the 10-year study period. The checkup of probands consists of physical examination, arteriovenous malformation exploration and and genetic testing (ACVRL1 and ENG sequence analysis). The family screening of HHT consists of physical examination and screening for the family-specific mutation of each at-risk individual, and furthermore, arteriovenous malformation exploration in individuals with suspected/definite HHT and/or carrying the mutation. Twenty-five definite HHT patients were explored: 7 of them by the I7800 review, 1 by the R0400 review, 3 were de novo diagnosed, and the remaining 14 were explored by the systematic family screening. Considering the 20 patients alive at the end of the study period and the unavailable 5 potential HHT patients and 12 at-risk family members, the HHT prevalence is estimated to be 1:6090-1:11267 in our study area, implying our algorithm's effectivity in the stratified population screening of HHT.

[Genetic diagnostics of hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu disease)]. / A herediter haemorrhagiás teleangiectasia (Osler­Weber­Rendu-kór) genetikai diagnosztikája.

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.