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UNC80 mutation causes a syndrome of hypotonia, severe intellectual disability, dyskinesia and dysmorphism, similar to that caused by mutations in its interacting cation channel NALCN
  1. Yonatan Perez1,
  2. Rotem Kadir1,
  3. Michael Volodarsky1,
  4. Iris Noyman2,
  5. Hagit Flusser3,
  6. Zamir Shorer2,
  7. Libe Gradstein4,
  8. Ramon Y Birnbaum5,
  9. Ohad S Birk1,6
  1. 1The Morris Kahn Laboratory of Human Genetics, National Institute for Biotechnology in the Negev, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
  2. 2Pediatric Neurology Unit, Division of Pediatrics, Faculty of Health Sciences, Soroka University Medical Center, Ben-Gurion University of the Negev, Beer Sheva, Israel
  3. 3Zussman Child Development Center, Faculty of Health Sciences, Soroka University Medical Center, Ben-Gurion University of the Negev, Beer Sheva, Israel
  4. 4Department of Ophthalmology, Faculty of Health Sciences, Soroka Medical Center and Clalit Health Services, Ben-Gurion University of the Negev, Beer Sheva, Israel
  5. 5Department of Life Sciences, Faculty of Natural Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
  6. 6Genetics Institute, Soroka University Medical Center, Ben-Gurion University of the Negev, Beer Sheva, Israel
  1. Correspondence to Professor Ohad S Birk, Genetics Institute, Soroka Medical Center, Ben-Gurion University of the Negev, PO Box 151, Beer Sheva 84101, Israel; obirk{at}bgu.ac.il

Abstract

Background A syndrome of profound hypotonia, intellectual disability, intrauterine growth retardation with subsequent failure to thrive, dyskinesia and epilepsy was diagnosed in Bedouin Israeli families. Mild dysmorphism was evident: plagiocephaly, broad forehead with prominent nose, smooth philtrum and congenital esotropia. We set out to decipher the molecular basis of this syndrome.

Methods Genome-wide linkage analysis and fine mapping were done. Whole exome sequencing data were filtered for candidate variants within locus. Validation and segregation of the mutation was assayed via Sanger sequencing. UNC80 expression pattern was analysed through reverse transcription PCR.

Results Homozygosity mapping followed by fine mapping identified a 7.5 Mb disease-associated locus (logarithm of odds score 3.5) on chromosome 2. Whole exome and Sanger sequencing identified a single homozygous nonsense mutation within this locus, segregating within the families as expected for recessive heredity and not found in a homozygous state in 150 Bedouin controls: c.151C>T, p.(R51*) in UNC80.

Conclusions The syndrome described is caused by a mutation in UNC80, truncating most of the 3258 amino acids highly conserved encoded protein, that has no known motifs. UNC80 bridges between UNC79 and the cation channel NALCN, enabling NALCN's role in basal Na+ leak conductance in neurons, essential for neuronal function. The phenotype caused by the UNC80 mutation resembles that previously described for homozygous NALCN mutations.

  • Clinical genetics
  • Molecular genetics
  • Neurology
  • Linkage

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