Bi-allelic NRCAM Variants Lead to a Neurodevelopmental Disorder Characterized by Developmental Delay, Hypotonia, Peripheral Neuropathy or Spasticity

Alina Kurolap ¹ Florian Kreuder ³ Claudia Gonzaga-Jauregui ⁴ Morasha Plesser Duvdevani ^5,6 Tamar Harel ^5,6 Luna Tammer ² Baozhong Xin ⁷ Somayeh Bakhtiari ^8,9 James Rice ¹⁰ Clare L. Van Eyk ¹⁰ Jozef Gecz ^10,11 Jean K. Mah ¹² Derek Atkinson ^13,14 Heidi Cope ¹⁵ Jennifer A. Sullivan ¹⁵ Alon M. Douek ³ Daniel Colquhoun ³ Jason Henry ¹⁶ Donald Wlodkowic ¹⁶ Yesim Parman ¹⁷ Ayşe Candayan ¹⁸ Elif Kocasoy-Orhan ¹⁷ Anat Ilivitzki ¹⁹ Shiri Soudry ²⁰ Rina Leibu ²⁰ Fabian Glaser ²¹ Valerie Sency ⁷ Gil Ast ² Vandana Shashi ¹⁵ Michael C. Fahey ²² Esra Battaloğlu ¹⁸ Albena Jordanova ^14,23 Vardiella Meiner ^5,6 A. Micheil Innes ^12,24 Heng Wang ⁷ Orly Elpeleg ^5,6 Michael C. Kruer ^8,9 Jan Kaslin ³ Hagit Baris Feldman ^1,2

¹The Genetics Institute and Genomics Center, Tel Aviv Sourasky Medical Center, ישראל
²Sackler Faculty of Medicine, Tel Aviv University, ישראל
³Australian Regenerative Medicine Institute, Monash University, אוסטרליה
⁴Regeneron Genetics Center, Regeneron Pharmaceuticals Inc, ארצות הברית
⁵Department of Genetics, Hadassah Medical Center, ישראל
⁶Faculty of Medicine, Hebrew University of Jerusalem, ישראל
⁷-, DDC Clinic - Center for Special Needs Children, ארצות הברית
⁸Pediatric Movement Disorders Program, Division of Pediatric Neurology, Barrow Neurological Institute, Phoenix Children's Hospital, ארצות הברית
⁹Departments of Child Health, Neurology, and Cellular & Molecular Medicine, and Program in Genetics, University of Arizona College of Medicine-Phoenix, ארצות הברית
¹⁰Paediatric Rehabilitation, Women's and Children's Hospital, אוסטרליה
¹¹-, South Australian Health and Medical Research Institute, אוסטרליה
¹²Department of Pediatrics and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, קנדה
¹³-, Max Planck Institute of Immunobiology and Epigenetics, גרמניה
¹⁴Molecular Neurogenomics Group, VIB-UAntwerp Center for Molecular Neurology, University of Antwerp, בלגיה
¹⁵Division of Medical Genetics, Department of Pediatrics, Duke University Medical Center, ארצות הברית
¹⁶School of Science, RMIT University, אוסטרליה
¹⁷Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, תורכיה
¹⁸Department of Molecular Biology and Genetics, Bogaziçi University, תורכיה
¹⁹Pediatric Radiology Unit, Rambam Health Care Campus, ישראל
²⁰Department of Ophthalmology, Rambam Health Care Campus, ישראל
²¹The Lorry I. Lokey Interdisciplinary Center for Life Sciences and Engineering, Technion-Israel Institute of Technology, ישראל
²²Department of Pediatrics, Monash University, אוסטרליה
²³Molecular Medicine Center, Department of Medical Chemistry and Biochemistry, Medical University-Sofia, בולגריה
²⁴Department of Medical Genetics and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, קנדה

Cell adhesion molecules (CAMs) are membrane-bound proteins predominantly expressed in the CNS along principal axonal pathways. CAMs, such as L1CAM, NRCAM, CHL1 and NFASC, play key roles in nervous system development, neural cell differentiation and migration, axonal growth and guidance, myelination, and synapse formation. However, only L1CAM and NFASC have been associated with neurodevelopmental disease.

Here we describe 10 patients from eight families with bi-allelic variants in the neuronal cell adhesion molecule NRCAM, leading to a novel neurodevelopmental syndrome of varying severity, characterized by developmental delay/intellectual disability, hypotonia, peripheral neuropathy and/or spasticity. Computational analyses of NRCAM variants, which mostly cluster in the third fibronectin type III (Fn-III) domain, strongly suggest a deleterious effect on NRCAM protein structure and function, potentially hindering its ability to interact with other proteins. These findings are corroborated by previous in vitro studies of murine Nrcam-deficient cells, revealing abnormal neurite outgrowth, synaptogenesis and formation of nodes of Ranvier on myelinated axons. We performed studies on zebrafish nrcamaΔ mutants, revealing that mutant larvae displayed significantly altered swimming behavior compared to wild type larvae (p<0.03). Moreover, nrcamaΔ larvae displayed a trend towards increased amounts of α-tubulin and 5-HT fibers in the dorsal telencephalon, demonstrating an alteration in white matter tracts and projections.

Taken together, our study provides evidence that bi-allelic NRCAM disruption causes a variable form of a neurodevelopmental disorder, and broadens the knowledge on the role of NRCAM in nervous system development, and the growing role of the cell adhesion molecules family in the nervous system.