ORIGINAL ARTICLES

Noonan and cardio-facio-cutaneous syndromes: two clinically and genetically overlapping disorders

A-M Nyström¹, S Ekvall¹, E Berglund², M Björkqvist³, G Braathen⁴, K Duchen⁵, H Enell⁶, E Holmberg⁷, U Holmlund⁸, M Olsson-Engman⁹, G Annerén¹, M-L Bondeson¹

¹ Department of Genetics and Pathology, Uppsala University, SE-751 85 Uppsala, Sweden
² Department of Paediatrics, Central Hospital, Skellefteå, Sweden
³ Department of Paediatrics, University Hospital, Örebro, Sweden
⁴ Department of Paediatrics, Sahlgrenska University Hospital, Göteborg, Sweden
⁵ Department of Paediatrics University Hospital, Linköping, Sweden
⁶ Department of Paediatrics, Regional hospital of Halmstad, Sweden
⁷ Clinical Genetics, Sahlgrenska University Hospital, Göteborg, Sweden
⁸ Department of Paediatrics, Central Hospital, Västerås, Sweden
⁹ Department of Paediatrics, Regional Hospital, Karlskrona, Sweden

Professor G Annerén, Department of Genetics and Pathology, Uppsala University, SE-751 85 Uppsala, Sweden; goran.anneren{at}genpat.uu.se

Background: Noonan syndrome (NS) and cardio-facio-cutaneous syndrome (CFC) are related disorders associated with disrupted RAS/RAF/MEK/ERK signalling. NS, characterised by facial dysmorphism, congenital heart defects and short stature, is caused by mutations in the genes PTPN11, SOS1, KRAS and RAF1. CFC is distinguished from NS by the presence of ectodermal abnormalities and more severe mental retardation in addition to the NS phenotype. The genetic aetiology of CFC was recently assigned to four genes: BRAF, KRAS, MEK1 and MEK2.

Methods: A comprehensive mutation analysis of BRAF, KRAS, MEK1, MEK2 and SOS1 in 31 unrelated patients without mutations in PTPN11 is presented.

Results: Mutations were identified in seven patients with CFC (two in BRAF, one in KRAS, one in MEK1, two in MEK2 and one in SOS1). Two mutations were novel: MEK1 E203Q and MEK2 F57L. The SOS1 E433K mutation, identified in a patient diagnosed with CFC, has previously been reported in patients with NS. In one patient with NS, we also identified a mutation, BRAF K499E, that has previously been reported in patients with CFC. We thus suggest involvement of BRAF in the pathogenesis of NS also.

Conclusions: Taken together, our results indicate that the molecular and clinical overlap between CFC and NS is more complex than previously suggested and that the syndromes might even represent allelic disorders. Furthermore, we suggest that the diagnosis should be refined to, for example, NS–PTPN11-associated or CFC–BRAF-associated syndromes after the genetic defect has been established, as this may affect the prognosis and treatment of the patients.

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This article has been cited by other articles:

• Neri, G, Allanson, J, Kavamura, M I (2008). No reason yet to change diagnostic criteria for Noonan, Costello and cardio-facio-cutaneous syndromes. J. Med. Genet. 45: 832-832 [Full Text]