An ancestral 10-bp repeat expansion in VWA1 causes recessive hereditary motor neuropathy
Authors: Pagnamenta Alistair T , Kaiyrzhanov Rauan , Zou Yaqun , Da'as Sahar I , Maroofian Reza , Donkervoort Sandra , Dominik Natalia , Lauffer Marlen , Ferla Matteo P , Orioli Andrea , Giess Adam , Tucci Arianna , Beetz Christian , Sedghi Maryam , Ansari Behnaz , Barresi Rita , Basiri Keivan , Cortese Andrea , Elgar Greg , Fernandez-Garcia Miguel A , Yip Janice , Foley A Reghan , Gutowski Nicholas , Jungbluth Heinz , Lassche Saskia , Lavin Tim , Marcelis Carlo , Marks Peter , Marini-Bettolo Chiara , Medne Livija , Moslemi Ali-Reza , Sarkozy Anna , Reilly Mary M , Muntoni Francesco , Millan Francisca , Muraresku Colleen C , Need Anna C , Nemeth Andrea H , Neuhaus Sarah B , Norwood Fiona , O'Donnell Marie , O’Driscoll Mary , Rankin Julia , Yum Sabrina W , Zolkipli-Cunningham Zarazuela , Brusius Isabell , Wunderlich Gilbert ,   Genomics England Research Consortium, Ambrose John C , Arumugam Prabhu , Baple Emma L , Bleda Marta , Boardman-Pretty Freya , Boissiere Jeanne M , Boustred Christopher R , Brittain Helen , Caulfield Mark J , Chan Georgia C , Craig Clare E H , Daugherty Louise C , Burca Anna de , Devereau Andrew , Elgar Greg , Foulger Rebecca E , Fowler Tom , Furió-Tarí Pedro , Giess Adam , Hackett Joanne M , Halai Dina , Hamblin Angela , Henderson Shirley , Holman James E , Hubbard Tim J P , ibáñez Kristina , Jackson Rob , Jones Louise J , Kasperaviciute Dalia , Kayikci Melis , Kousathanas Athanasios , Lahnstein Lea , Lawson Kay , Leigh Sarah E A , Leong Ivonne U S , Lopez Javier F , Maleady-Crowe Fiona , Mason Joanne , McDonagh Ellen M , Moutsianas Loukas , Mueller Michael , Murugaesu Nirupa , Need Anna C , O’Donovan Peter , Odhams Chris A , Orioli Andrea , Patch Christine , Pereira Mariana Buongermino , Perez-Gil Daniel , Polychronopoulos Dimitris , Pullinger John , Rahim Tahrima , Rendon Augusto , Riesgo-Ferreiro Pablo , Rogers Tim , Ryten Mina , Savage Kevin , Sawant Kushmita , Scott Richard H , Siddiq Afshan , Sieghart Alexander , Smedley Damian , Smith Katherine R , Smith Samuel C , Sosinsky Alona , Spooner William , Stevens Helen E , Stuckey Alexander , Sultana Razvan , Tanguy Mélanie , Thomas Ellen R A , Thompson Simon R , Tregidgo Carolyn , Tucci Arianna , Walsh Emma , Watters Sarah A , Welland Matthew J , Williams Eleanor , Witkowska Katarzyna , Wood Suzanne M , Zarowiecki Magdalena , Karakaya Mert , Wirth Brunhilde , Fakhro Khalid A , Tajsharghi Homa , Bönnemann Carsten G , Taylor Jenny C , Houlden Henry 
Published: November 2020

Abstract
The extracellular matrix comprises a network of macromolecules such as collagens, proteoglycans and glycoproteins. VWA1 (von Willebrand factor A domain containing 1) encodes a component of the extracellular matrix that interacts with perlecan/collagen VI, appears to be involved in stabilizing extracellular matrix structures, and demonstrates high expression levels in tibial nerve. Vwa1-deficient mice manifest with abnormal peripheral nerve structure/function; however, VWA1 variants have not previously been associated with human disease. By interrogating the genome sequences of 74 180 individuals from the 100K Genomes Project in combination with international gene-matching efforts and targeted sequencing, we identified 17 individuals from 15 families with an autosomal-recessive, non-length dependent, hereditary motor neuropathy and rare biallelic variants in VWA1. A single disease-associated allele p.(G25Rfs*74), a 10-bp repeat expansion, was observed in 14/15 families and was homozygous in 10/15. Given an allele frequency in European populations approaching 1/1000, the seven unrelated homozygote individuals ascertained from the 100K Genomes Project represents a substantial enrichment above expected. Haplotype analysis identified a shared 220 kb region suggesting that this founder mutation arose &gt;7000 years ago. A wide age-range of patients (6–83 years) helped delineate the clinical phenotype over time. The commonest disease presentation in the cohort was an early-onset (mean 2.0 ± 1.4 years) non-length-dependent axonal hereditary motor neuropathy, confirmed on electrophysiology, which will have to be differentiated from other predominantly or pure motor neuropathies and neuronopathies. Because of slow disease progression, ambulation was largely preserved. Neurophysiology, muscle histopathology, and muscle MRI findings typically revealed clear neurogenic changes with single isolated cases displaying additional myopathic process. We speculate that a few findings of myopathic changes might be secondary to chronic denervation rather than indicating an additional myopathic disease process. Duplex reverse transcription polymerase chain reaction and immunoblotting using patient fibroblasts revealed that the founder allele results in partial nonsense mediated decay and an absence of detectable protein. CRISPR and morpholino vwa1 modelling in zebrafish demonstrated reductions in motor neuron axonal growth, synaptic formation in the skeletal muscles and locomotive behaviour. In summary, we estimate that biallelic variants in VWA1 may be responsible for up to 1% of unexplained hereditary motor neuropathy cases in Europeans. The detailed clinical characterization provided here will facilitate targeted testing on suitable patient cohorts. This novel disease gene may have previously evaded detection because of high GC content, consequential low coverage and computational difficulties associated with robustly detecting repeat-expansions. Reviewing previously unsolved exomes using lower QC filters may generate further diagnoses.