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Short report
Encephalocraniocutaneous lipomatosis phenotype associated with mosaic biallelic pathogenic variants in the NF1 gene
  1. Steven Smeijers1,
  2. Hilde Brems2,
  3. Alexander Verhaeghe3,
  4. Wim van Paesschen4,
  5. Johannes van Loon1,
  6. Seppe Van der Auweraer2,
  7. Raf Sciot5,
  8. Dietmar Rudolf Thal5,6,
  9. Lieven Lagae7,
  10. Eric Legius2,
  11. Tom Theys1
  1. 1 Department of Neurosurgery, KU Leuven University Hospitals, Leuven, Belgium
  2. 2 Center for Human Genetics and Department of Human Genetics, KU Leuven University Hospitals, Leuven, Belgium
  3. 3 Department of Neurosurgery, AZ Sint-Jan AV, Brugge, Belgium
  4. 4 Department of Neurology, KU Leuven University Hospitals, Leuven, Belgium
  5. 5 Department of Pathology, KU Leuven University Hospitals, Leuven, Belgium
  6. 6 Laboratory for Neuropathology, Department of Imaging and Pathology and Leuven Brain Institute, KULeuven, Leuven, Belgium
  7. 7 Department of Paediatric Neurology, University of Leuven, Leuven, Belgium
  1. Correspondence to Dr Steven Smeijers, Department of Neurosurgery, KU Leuven University Hospitals, Leuven, Belgium; steven.smeijers{at}uzleuven.be

Abstract

Encephalocraniocutaneous lipomatosis (ECCL) is a sporadic congenital condition characterised by ocular, cutaneous and central nervous system involvement. Mosaic activating variants in FGFR1 and KRAS have been reported in several individuals with this syndrome. We report on a patient with neurofibromatosis type 1 (NF1) with a germline pathogenic variant in the NF1 gene and an ECCL phenotype, suggesting ECCL to be part of a spectrum of malformations associated with NF1 pathogenic variants. An anatomical hemispherectomy was performed for intractable epilepsy. Through genetic analysis of blood, cerebral tissue and giant cell lesions in both jaws, we identified the germline NF1 pathogenic variant in all samples and a second-hit pathogenic NF1 variant in cerebral tissue and both giant cell lesions. Both NF1 variants were located on different alleles resulting in somatic mosaicism for a biallelic NF1 inactivation originating in early embryogenesis (second-hit mosaicism or Happle type 2 mosaicism). The biallelic deficit in NF1 in the left hemicranium explains the severe localised, congenital abnormality in this patient. Identical first and second-hit variants in a giant cell lesion of both upper and lower jaws provide confirmatory evidence for an early embryonic second hit involving at least the neural crest. We suggest that the ECCL phenotype may be part of a spectrum of congenital problems associated with mosaic NF1 nullisomy originating during early embryogenesis. The biallelic NF1 inactivation during early embryogenesis mimics the severe activation of the RAS-MAPK pathway seen in ECCL caused by embryonic mosaic activating FGFR1 and KRAS variants in the cranial region. We propose that distinct mechanisms of mosaicism can cause the ECCL phenotype through convergence on the RAS-MAPK pathway.

  • Phenotype
  • Neurology
  • Genetics
  • Neurosurgery

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Footnotes

  • SS and HB are joint first authors.

  • Correction notice This article has been corrected since it was published online first. ORCID IDs have been added, and a couple of corrections in the text have been implemented.

  • Contributors The following authors participated, respectively, in conduct—SS, HB, AV, SVdA, RS, DRT, EL, TT; in reporting—SS, HB, WvP, JvL, RS, DRT, LL, EL, TT; in conception and design—SS, HB, WvP, JvL, LL, EL, TT; in acquisition of data—SS, HB, AV, WvP, SVdA, RS, DRT, LL, EL, TT; in data analysis and interpretation—SS, HB, WvP, JvL, SVdA, LL, RS, DRT, EL, TT.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests DRT received speaker honorary from Biogen (USA), travel reimbursement from UCB (Belgium), and collaborated with Novartis Pharma (Switzerland), Probiodrug (Germany), GE-Healthcare (UK) and Janssen Pharmaceutical Companies (Belgium). DRT receives grants from Fonds Wetenschappelijk Onderzoek (FWO (Vlaanderen): G0F8516N, G065721N), Stichting Alzheimer Onderzoek (SAO-FRA (Belgium): 2020/017) and KU-Leuven Internal Funding (C14/22/132; C3/20/057). All other authors report no conflict of interest.

  • Provenance and peer review Not commissioned; externally peer reviewed.