title: Phenotypic and molecular insights into CASK-related disorders in males.
abstract: BACKGROUND
  Heterozygous loss-of-function mutations in the X-linked CASK gene cause progressive microcephaly with pontine and cerebellar hypoplasia (MICPCH) and severe intellectual disability (ID) in females. Different CASK mutations have also been reported in males. The associated phenotypes range from nonsyndromic ID to Ohtahara syndrome with cerebellar hypoplasia. However, the phenotypic spectrum in males has not been systematically evaluated to date.
  
  
  METHODS
  We identified a CASK alteration in 8 novel unrelated male patients by targeted Sanger sequencing, copy number analysis (MLPA and/or FISH) and array CGH. CASK transcripts were investigated by RT-PCR followed by sequencing. Immunoblotting was used to detect CASK protein in patient-derived cells. The clinical phenotype and natural history of the 8 patients and 28 CASK-mutation positive males reported previously were reviewed and correlated with available molecular data.
  
  
  RESULTS
  CASK alterations include one nonsense mutation, one 5-bp deletion, one mutation of the start codon, and five partial gene deletions and duplications; seven were de novo, including three somatic mosaicisms, and one was familial. In three subjects, specific mRNA junction fragments indicated in tandem duplication of CASK exons disrupting the integrity of the gene. The 5-bp deletion resulted in multiple aberrant CASK mRNAs. In fibroblasts from patients with a CASK loss-of-function mutation, no CASK protein could be detected. Individuals who are mosaic for a severe CASK mutation or carry a hypomorphic mutation still showed detectable amount of protein.
  
  
  CONCLUSIONS
  Based on eight novel patients and all CASK-mutation positive males reported previously three phenotypic groups can be distinguished that represent a clinical continuum: (i) MICPCH with severe epileptic encephalopathy caused by hemizygous loss-of-function mutations, (ii) MICPCH associated with inactivating alterations in the mosaic state or a partly penetrant mutation, and (iii) syndromic/nonsyndromic mild to severe ID with or without nystagmus caused by CASK missense and splice mutations that leave the CASK protein intact but likely alter its function or reduce the amount of normal protein. Our findings facilitate focused testing of the CASK gene and interpreting sequence variants identified by next-generation sequencing in cases with a phenotype resembling either of the three groups.
authors.affiliation: Institute of Human Genetics, Heidelberg University, Heidelberg, Germany. ute.moog@med.uni-heidelberg.de.
authors.forename: Ute
authors.initials: U
authors.lastname: Moog
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246, Hamburg, Germany. t.bierhals@uke.de.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Bierhals
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246, Hamburg, Germany. k.brand@uke.de.
authors.forename: Kristina
authors.initials: K
authors.lastname: Brand
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246, Hamburg, Germany. mail@janbautsch.de.
authors.forename: Jan
authors.initials: J
authors.lastname: Bautsch
authors.affiliation: CeGaT GmbH, Tübingen, Germany. saskia.biskup@cegat.de.
authors.forename: Saskia
authors.initials: S
authors.lastname: Biskup
authors.affiliation: Universitätskinderklinik, Universitätsklinikum Magdeburg, Magdeburg, Germany. thomas.brune@klinikum-lippe.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Brune
authors.affiliation: Klinik und Poliklinik für Kinder- und Jugendmedizin, Neuropädiatrie, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany. j.denecke@uke.de.
authors.forename: Jonas
authors.initials: J
authors.lastname: Denecke
authors.affiliation: Department of Clinical Genetics and School for Oncology & Developmental Biology (GROW), Maastricht UMC+, Maastricht, The Netherlands. c.dedie@mumc.nl.
authors.forename: Christine E
authors.initials: CE
authors.lastname: de Die-Smulders
authors.affiliation: Institute of Human Genetics, Heidelberg University, Heidelberg, Germany. Christina.Evers@med.uni-heidelberg.de.
authors.forename: Christina
authors.initials: C
authors.lastname: Evers
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246, Hamburg, Germany. m.hempel@uke.de.
authors.forename: Maja
authors.initials: M
authors.lastname: Hempel
authors.affiliation: Klinik für Kinder- und Jugendmedizin, Universitätsmedizin Göttingen, Göttingen, Germany. hennekem@med.uni-goettingen.de.
authors.forename: Marco
authors.initials: M
authors.lastname: Henneke
authors.affiliation: Department of Human Genetics, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands. Helger.IJntema@radboudumc.nl.
authors.forename: Helger
authors.initials: H
authors.lastname: Yntema
authors.affiliation: Center for Medical Genetics, Ghent University, Ghent, Belgium. bjorn.menten@ugent.be.
authors.forename: Björn
authors.initials: B
authors.lastname: Menten
authors.affiliation: Section of Neuropediatrics, Center for Child and Adolescent Medicine, Heidelberg, Germany. joachim.pietz@med.uni-heidelberg.de.
authors.forename: Joachim
authors.initials: J
authors.lastname: Pietz
authors.affiliation: Department of Human Genetics, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands. Rolph.Pfundt@radboudumc.nl.
authors.forename: Rolph
authors.initials: R
authors.lastname: Pfundt
authors.affiliation: Institut für Humangenetik, Medizinische Hochschule Hannover, Hannover, Germany. Schmidtke.Joerg@mh-hannover.de.
authors.forename: Jörg
authors.initials: J
authors.lastname: Schmidtke
authors.affiliation: Institut für Zell- und Molekularpathologie, Medizinische Hochschule Hannover, Hannover, Germany. Steinemann.Doris@mh-hannover.de.
authors.forename: Doris
authors.initials: D
authors.lastname: Steinemann
authors.affiliation: Department of Clinical Genetics and School for Oncology & Developmental Biology (GROW), Maastricht UMC+, Maastricht, The Netherlands. c.stumpel@mumc.nl.
authors.forename: Constance T
authors.initials: CT
authors.lastname: Stumpel
authors.affiliation: Centre de Génétique Humaine, Université de Franche-Comté, Besançon, France. vmald@hotmail.com.
authors.forename: Lionel
authors.initials: L
authors.lastname: Van Maldergem
authors.affiliation: Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246, Hamburg, Germany. kkutsche@uke.de.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Kutsche
mesh_terms: D000293:Adolescent; D000328:Adult; D002531:Cerebellum / Q000002:abnormalities / Q000201:enzymology; D002648:Child; D002675:Child, Preschool; D002658:Developmental Disabilities / Q000201:enzymology / Q000209:etiology / Q000235:genetics; D051528:Guanylate Kinases / Q000235:genetics*; D006801:Humans; D007223:Infant; D008607:Intellectual Disability / Q000201:enzymology / Q000209:etiology / Q000235:genetics; D008297:Male; D008831:Microcephaly / Q000150:complications / Q000201:enzymology* / Q000235:genetics; D008875:Middle Aged; D009154:Mutation; D009421:Nervous System Malformations / Q000201:enzymology / Q000209:etiology / Q000235:genetics; D010641:Phenotype; D055815:Young Adult
chemical_list: C106868:CASK kinases; D051528:Guanylate Kinases