HRAS germline mutations impair LKB1/AMPK signaling and mitochondrial homeostasis in Costello syndrome models.

Germline mutations that activate genes in the canonical RAS/MAPK signaling pathway are responsible for rare human developmental disorders known as RASopathies. Here, we analyzed the molecular determinants of Costello syndrome (CS) using a mouse model expressing HRAS p.G12S, patient skin fibroblasts, hiPSC-derived human cardiomyocytes, a HRAS p.G12V zebrafish model, and human fibroblasts expressing lentiviral constructs carrying HRAS p.G12S or HRAS p.G12A mutations. The findings revealed alteration of mitochondrial proteostasis and defective oxidative phosphorylation in the heart and skeletal muscle of CS mice that were also found in the cell models of the disease. The underpinning mechanisms involved the inhibition of the AMPK signaling pathway by mutant forms of HRAS, leading to alteration of mitochondrial proteostasis and bioenergetics. Pharmacological activation of mitochondrial bioenergetics and quality control restored organelle function in HRAS p.G12A and p.G12S cell models, reduced left ventricle hypertrophy in CS mice, and diminished the occurrence of developmental defects in the CS zebrafish model. Collectively, these findings highlight the importance of mitochondrial proteostasis and bioenergetics in the pathophysiology of RASopathies and suggest that patients with CS may benefit from treatment with mitochondrial modulators.

Exome sequencing as a second-tier diagnostic approach for clinically suspected dysferlinopathy patients.

INTRODUCTION: Autosomal recessive muscular dystrophies are heterogeneous genetic disorders, with 39 genes currently implicated. Genetic diagnosis using targeted single-gene analysis by Sanger sequencing yields negative results in 10-20% of samples, warranting clinical re-evaluation and time-consuming testing of additional genes. This applies to dysferlinopathies caused by mutations in the gene encoding dysferlin (DYSF), which presents mainly as limb-girdle muscular dystrophy (LGMD) or distal myopathy. METHODS: We evaluated exome sequencing associated with data filtering for selected genes as a second-tier approach for genetic diagnosis in a cohort of 37 patients with an initial negative result on targeted DYSF analysis. RESULTS: Exome sequencing allowed for establishing (16%) or suggesting (8%) the molecular diagnosis by implicating other known LGMD or distal myopathy genes or by revealing DYSF mutations previously missed using mutation-screening techniques with incomplete detection yields. CONCLUSIONS: Exome sequencing associated with data filtering constitutes an efficient second-tier analysis for genes implicated in LGMD or distal myopathies.

A Collodion Baby with Facial Dysmorphism, Limb Anomalies, Pachygyria and Genital Hypoplasia: A Mild Form of Neu-Laxova Syndrome or a New Entity?

Neu-Laxova syndrome is a rare, lethal, autosomal recessive disorder characterized by intrauterine growth retardation, central nervous system anomalies, skin findings, such as ichthyosis, edema, collodion baby and harlequin fetus, facial dysmorphic features, limb anomalies and genital hypoplasia. Although it is generally a lethal condition, cases of such patients who lived beyond 6 months and 10 months of age have been reported. Here, we describe an 8-year-old boy who was born with collodion membrane, facial dysmorphic features, limb anomalies, genital hypoplasia and pachygyria. He had no major health problems over the course of 8 years of follow-up, except for mild mental/motor retardation, ichthyosis, facial dysmorphic features and limb anomalies. Based on these features, we suggest that because Neu-Laxova syndrome represents a heterogeneous phenotype, our case may be a milder variant of this syndrome or a new genetic entity.