Novel Digital Anomalies, Hippocampal Atrophy, and Mutations Expand the Genotypic and Phenotypic Spectra of CNKSR2 in the Houge Type of X-Linked Syndromic Intellectual Development Disorder (MRXSHG)

Mohammad Reza Ghasemi, Sahand Tehrani Fateh, Afif Ben-Mahmoud, Vijay Gupta, Lara G. Stühn, Gaetan Lesca, Nicolas Chatron, Konrad Platzer, Patrick Edery, Hossein Sadeghi, Bertrand Isidor, Benjamin Cogné, Heidi L. Schulz, Ilona Krauspe-Stübecke, Radhakrishnan Periyasamy, Sheela Nampoothiri, Reza Mirfakhraie, Sahar Alijanpour, Steffen Syrbe, Ulrich PfeiferStephanie Spranger, Kathrin Grundmann-Hauser, Tobias B. Haack, Maria T. Papadopoulou, Tayrine da Silva Gonçalves, Eleni Panagiotakaki, Alexis Arzimanoglou, Seyed Hassan Tonekaboni, Massimiliano Rossi, G. Christoph Korenke, Yves Lacassie, Mi Hyeon Jang, Lawrence C. Layman, Mohammad Miryounesi, Hyung Goo Kim*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The Houge type of X-linked syndromic intellectual developmental disorder (MRXSHG) encompasses a spectrum of neurodevelopmental disorders characterized by intellectual disability (ID), language/speech delay, attention issues, and epilepsy. These conditions arise from hemizygous or heterozygous deletions, along with point mutations, affecting CNKSR2, a gene located at Xp22.12. CNKSR2, also known as CNK2 or MAGUIN, functions as a synaptic scaffolding molecule within the neuronal postsynaptic density (PSD) of the central nervous system. It acts as a link connecting postsynaptic structural proteins, such as PSD95 and S-SCAM, by employing multiple functional domains crucial for synaptic signaling and protein–protein interactions. Predominantly expressed in dendrites, CNKSR2 is vital for dendritic spine morphogenesis in hippocampal neurons. Its loss-of-function variants result in reduced PSD size and impaired hippocampal development, affecting processes including neuronal proliferation, migration, and synaptogenesis. We present 15 patients including three from the MENA (Middle East and North Africa), a region with no documented mutations in CNKSR2. Each individual displays unique clinical presentations that encompass developmental delay, ID, language/speech delay, epilepsy, and autism. Genetic analyses revealed 14 distinct variants in CNKSR2, comprising five nonsense, three frameshift, two splice, and four missense variants, of which 13 are novel. The ACMG guidelines unanimously interpreted these 14 variants in 15 individuals as pathogenic, highlighting the detrimental impact of these CNKSR2 genetic alterations and confirming the molecular diagnosis of MRXSHG. Importantly, variants Ser767Phe and Ala827Pro may lead to proteasomal degradation or reduced PSD size, contributing to the neurodevelopmental phenotype. Furthermore, these two amino acids, along with another two affected by four missense variants, exhibit complete conservation in nine vertebrate species, illuminating their crucial role in the gene's functionality. Our study revealed unique new digital and brain phenotype, including pointed fingertips (fetal pads of fingertips), syndactyly, tapering fingers, and hippocampal atrophy. These novel clinical features in MRXSHG, combined with 13 novel variants, expand the phenotypic and genotypic spectra of MRXSHG associated with CNKSR2 mutations.

Original languageEnglish
Number of pages20
JournalAmerican Journal of Medical Genetics, Part A
Early online dateDec 2024
DOIs
Publication statusPublished - 20 Dec 2024

Keywords

  • Autism
  • Cnksr2
  • Cyth2
  • Hippocampal atrophy
  • Intellectual disability
  • Mrxshg
  • Pointed fingertips
  • Psd
  • Syndactyly
  • Tapering fingers

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