ONLINE MUTATION REPORT

De novo HRAS and KRAS mutations in two siblings with short stature and neuro-cardio-facio-cutaneous features

Oddmund Søvik¹, Suzanne Schubbert^2,*, Gunnar Houge^3,*, Solrun J Steine⁴, Gunnar Norgård⁵, Bernt Engelsen⁶, Pål R Njølstad^1,5, Kevin Shannon², Anders Molven⁷

¹ Section for Pediatrics, Department of Clinical Medicine, University of Bergen, Bergen, Norway
² Department of Pediatrics, University of California, San Fransisco, CA, USA
³ Department of Medical Genetics and Molecular Medicine, Haukeland University Hospital, Bergen, Norway
⁴ Section for Pathology, the Gade Institute, University of Bergen, Bergen, Norway
⁵ Department of Pediatrics, Haukeland University Hospital, Bergen, Norway
⁶ Department of Neurology, Haukeland University Hospital, Bergen, Norway
⁷ Department of Pathology, Haukeland University Hospital, Bergen, Norway

Correspondence to:
Correspondence to:
Professor A Molven
Section for Pathology, the Gade Institute, University of Bergen, Haukeland University Hospital, N-5021 Bergen, Norway; anders.molven{at}gades.uib.no

Mutations in genes involved in Ras signalling cause Noonan syndrome and other disorders characterised by growth disturbances and variable neuro-cardio-facio-cutaneous features. We describe two sisters, 46 and 31 years old, who presented with dysmorphic features, hypotonia, feeding difficulties, retarded growth and psychomotor retardation early in life. The patients were initially diagnosed with Costello syndrome, and autosomal recessive inheritance was assumed. Remarkably, however, we identified a germline HRAS mutation (G12A) in one sister and a germline KRAS mutation (F156L) in her sibling. Both mutations had arisen de novo. The F156L mutant K-Ras protein accumulated in the active, guanosine triphosphate-bound conformation and affected downstream signalling. The patient harbouring this mutation was followed for three decades, and her cardiac hypertrophy gradually normalised. However, she developed severe epilepsy with hippocampal sclerosis and atrophy. The occurrence of distinct de novo mutations adds to variable expressivity and gonadal mosaicism as possible explanations of how an autosomal dominant disease may manifest as an apparently recessive condition.

Abbreviations: CFC, cardio-facio-cutaneous; CS, Costello’s syndrome; GTP, guanosine triphosphate; MAPK, mitogen-activated protein kinase; NF1, neurofibromatosis type 1; NS, Noonan’s syndrome; SNP, single nucleotide polymorphism

Keywords: Costello syndrome; cardio-facio-cutaneous syndrome; Noonan syndrome; MAPK signalling pathway; Ras genes

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