Severe neuroglycopenic symptoms due to nonketotic hypoglycemia in children with cardio-facio-cutaneous syndrome

Cardio-facio-cutaneous syndrome (CFC) (OMIM 115150) is a congenital disease caused by constitutive activation of the Raf/MEK/ERK signaling cascade. Unlike aspects of morphological anomalies, metabolic functions related to the disease have garnered little attention. We present severe neuroglycopenic symptoms due to nonketotic hypoglycemia in two children with CFC (Case 1, a 4-year-old male with c.389A > G heterozygous variant in MAP2K1; Case 2, a 3-year-old male with c.770A > G heterozygous variant in BRAF). Case 1 exhibited a nonketotic hypoglycemic coma and clustered left-hemispheric convulsions despite receiving infusion therapy, leading to severe sequelae with choreoathetosis. Brain magnetic resonance imaging of Case 1 showed T2-elongation with restricted diffusion on the bilateral basal ganglia and thalamus, with the dominance of the right putamen. Case 2 presented a prolonged generalized seizure as an initial clinical symptom but fully recovered. The presence of growth hormone and cortisol deficiency was ruled out in both cases. Blood spots acylcarnitine profiles excluded the co-occurrence of mitochondrial HMG-CoA synthase deficiency and HMG-CoA lyase deficiency. These cases demonstrate the potential vulnerability to nonketotic hypoglycemia, especially during lipid shortages. As children with CFC frequently have difficulties feeding, we suggest great attention should be paid to the potential risk of severe nonketotic hypoglycemia.

GTP hydrolysis is modulated by Arg34 in the RASopathy-associated KRASP34R

RAS proteins are commonly mutated in cancerous tumors, but germline RAS mutations are also found in RASopathy syndromes such as Noonan syndrome (NS) and cardiofaciocutaneous (CFC) syndrome. Activating RAS mutations can be subclassified based on their activating mechanisms. Understanding the structural basis for these mechanisms may provide clues for how to manage associated health conditions. We determined high-resolution X-ray structures of the RASopathy mutant KRASP34R seen in NS and CFCS. GTP and GDP-bound KRASP34R crystallized in multiple forms, with each lattice consisting of multiple protein conformations. In all GTP-bound conformations, the switch regions are not compatible with GAP binding, suggesting a structural mechanism for the GAP insensitivity of this RAS mutant. However, GTP-bound conformations are compatible with intrinsic nucleotide hydrolysis, including one that places R34 in a position analogous to the GAP arginine finger or intrinsic arginine finger found in heterotrimeric G proteins, which may support intrinsic GTP hydrolysis. We also note that the affinity between KRASP34R and RAF-RBD is decreased, suggesting another possible mechanism for dampening of RAS signaling. These results may provide a foothold for development of new mutation-specific strategies to address KRASP34R -driven diseases.

BRaf signaling principles unveiled by large-scale human mutation analysis with a rapid lentivirus-based gene replacement method

Rapid advances in genetics are linking mutations on genes to diseases at an exponential rate, yet characterizing the gene-mutation-cell-behavior relationships essential for precision medicine remains a daunting task. More than 350 mutations on small GTPase BRaf are associated with various tumors, and ∼40 mutations are associated with the neurodevelopmental disorder cardio-facio-cutaneous syndrome (CFC). We developed a fast cost-effective lentivirus-based rapid gene replacement method to interrogate the physiopathology of BRaf and ∼50 disease-linked BRaf mutants, including all CFC-linked mutants. Analysis of simultaneous multiple patch-clamp recordings from 6068 pairs of rat neurons with validation in additional mouse and human neurons and multiple learning tests from 1486 rats identified BRaf as the key missing signaling effector in the common synaptic NMDA-R-CaMKII-SynGap-Ras-BRaf-MEK-ERK transduction cascade. Moreover, the analysis creates the original big data unveiling three general features of BRaf signaling. This study establishes the first efficient procedure that permits large-scale functional analysis of human disease-linked mutations essential for precision medicine.

Enhanced SMAD1 Signaling Contributes to Impairments of Early Development in CFC-iPSCs

Cardio-facio-cutaneous (CFC) syndrome is a developmental disorder caused by constitutively active ERK signaling manifesting mainly from BRAF mutations. Little is known about the role of elevated ERK signaling in CFC syndrome during early development. Here, we show that both SMAD1 and ERK signaling pathways may contribute to the developmental defects in CFC syndrome. Induced pluripotent stem cells (iPSCs) derived from dermal fibroblasts of a CFC syndrome patient (CFC-iPSCs) revealed early developmental defects in embryoid body (EB) development, β-catenin localization, and neuronal differentiation. Both SMAD1 and ERK signalings were significantly activated in CFC-iPSCs during EB formation. Most of the β-catenin was dissociated from the membrane and preferentially localized into the nucleus in CFC-EBs. Furthermore, activation of SMAD1 signaling recapitulated early developmental defects in wild-type iPSCs. Intriguingly, inhibition of SMAD1 signaling in CFC-iPSCs rescued aberrant EB morphology, impaired neuronal differentiation, and altered β-catenin localization. These results suggest that SMAD1 signaling may be a key pathway contributing the pathogenesis of CFC syndrome during early development.

A girl with Cardio-facio-cutaneous syndrome complicated with status epilepticus and acute encephalopathy

We report a six-year-old girl with Cardio-facio-cutaneous (CFC) syndrome who developed acute encephalopathy after the recurrence of status epilepticus. While epileptic encephalopathy and severe epilepsy have been mentioned as frequent complications of the CFC syndrome, no previous reports have shown a case of the CFC syndrome complicated with acute encephalopathy. Here we discuss the possibility for the linkage between the development of acute encephalopathy and CFC syndrome which is generally susceptible to seizures or epilepsy.