We report on a fourth familial case with transmission of CFC syndrome from father to son due to a novel heterozygous sequence change c.376A>G (p.N126D) in exon 3 of MEK2 gene.
The patient showed a paternally inherited 16p13.11 microduplication and a de novo 19p13.3 microdeletion involving the mitogen-activated protein kinase kinase 2 gene (MAP2K2), in which mutations cause the cardio-facio-cutaneous (CFC) syndrome.
The recent discoveries of germline HRAS mutations in patients with Costello syndrome and mutations in BRAF, MEK1, and MEK2 in CFC syndrome uncovered the biologic mechanism for the shared phenotypic findings based on the close interaction of the affected gene products within the MAP kinase pathway.
Together with recent findings of BRAF, MEK1, and MEK2 mutations in CFC syndrome and HRAS mutations in Costello syndrome, another clinically related disorder, it has now become clear that Noonan-like features (short stature, relative macrocephaly, facial anomalies, learning difficulties) that are found in these three related disorders are a result of constitutive activation of the Ras-Raf-extracellular signal-regulated and mitogen-activated protein kinase pathway.
None of the patients of our series with CFC syndrome (with germline BRAF or MAP2K1/MAP2K2 mutation - n = 121) or Costello syndrome (with HRAS mutation - n = 35) had an ALL.
Children born with germ-line mutations in BRAF, MEK1 or MEK2 develop cardio-facio-cutaneous (CFC) syndrome, an autosomal dominant syndrome characterized by a distinctive facial appearance, heart defects, skin and hair abnormalities and mental retardation.
Clinical review of known individuals with MEK1/MEK2 mutations suggests that these patients show dysmorphic features, ectodermal abnormalities and cognitive deficit similar to what was observed in BRAF-mutated patients and in the general CFCS population.
Cardiofaciocutaneous syndrome (CFCS) is a rare developmental disorder that is phenotypically similar to Noonan syndrome and is associated with mutations in BRAF, MEK1, MEK2, and KRAS.
In recent years, vertical transmission of CFC has been seen in mutations involving the MEK2 and KRAS genes, but has not previously been reported with BRAF mutations.
Moreover, mutations in several genes associated with the Ras-mitogen-activated protein kinase (MAPK) pathway, including HRAS, BRAF, MEK1, and MEK2 were identified in patients with Costello syndrome and CFC syndrome.
We define the phenotype of seven patients with de novo deletions of chromosome 19p13.3 including MEK2; they present with a distinct phenotype but have overlapping features with CFC syndrome.
This discovery provided a clue to identification of germline mutations in Kirsten-RAS (KRAS), BRAF and mitogen-activated protein kinase kinase 1 and 2 (MAP2K1/MAP2K2) in patients with CFC syndrome.
Approximately 25% of individuals with CFC have mutations in either MEK1 or MEK2 that lead to increased MEK kinase activity as judged by increased phosphorylation of its downstream effector ERK.
Approximately 25% of individuals with CFC have mutations in either MEK1 or MEK2 that lead to increased MEK kinase activity as judged by increased phosphorylation of its downstream effector ERK.