SPRED2 loss-of-function causes a recessive Noonan syndrome-like phenotype.

Upregulated signal flow through RAS and the mitogen-associated protein kinase (MAPK) cascade is the unifying mechanistic theme of the RASopathies, a family of disorders affecting development and growth. Pathogenic variants in more than 20 genes have been causally linked to RASopathies, the majority having a dominant role in promoting enhanced signaling. Here, we report that SPRED2 loss of function is causally linked to a recessive phenotype evocative of Noonan syndrome. Homozygosity for three different variants-c.187C>T (p.Arg63∗), c.299T>C (p.Leu100Pro), and c.1142_1143delTT (p.Leu381Hisfs∗95)-were identified in four subjects from three families. All variants severely affected protein stability, causing accelerated degradation, and variably perturbed SPRED2 functional behavior. When overexpressed in cells, all variants were unable to negatively modulate EGF-promoted RAF1, MEK, and ERK phosphorylation, and time-course experiments in primary fibroblasts (p.Leu100Pro and p.Leu381Hisfs∗95) documented an increased and prolonged activation of the MAPK cascade in response to EGF stimulation. Morpholino-mediated knockdown of spred2a and spred2b in zebrafish induced defects in convergence and extension cell movements indicating upregulated RAS-MAPK signaling, which were rescued by expressing wild-type SPRED2 but not the SPRED2Leu381Hisfs∗95 protein. The clinical phenotype of the four affected individuals included developmental delay, intellectual disability, cardiac defects, short stature, skeletal anomalies, and a typical facial gestalt as major features, without the occurrence of the distinctive skin signs characterizing Legius syndrome. These features, in part, characterize the phenotype of Spred2-/- mice. Our findings identify the second recessive form of Noonan syndrome and document pleiotropic consequences of SPRED2 loss of function in development.

WNT Signaling Perturbations Underlie the Genetic Heterogeneity of Robinow Syndrome.

Locus heterogeneity characterizes a variety of skeletal dysplasias often due to interacting or overlapping signaling pathways. Robinow syndrome is a skeletal disorder historically refractory to molecular diagnosis, potentially stemming from substantial genetic heterogeneity. All current known pathogenic variants reside in genes within the noncanonical Wnt signaling pathway including ROR2, WNT5A, and more recently, DVL1 and DVL3. However, ∼70% of autosomal-dominant Robinow syndrome cases remain molecularly unsolved. To investigate this missing heritability, we recruited 21 families with at least one family member clinically diagnosed with Robinow or Robinow-like phenotypes and performed genetic and genomic studies. In total, four families with variants in FZD2 were identified as well as three individuals from two families with biallelic variants in NXN that co-segregate with the phenotype. Importantly, both FZD2 and NXN are relevant protein partners in the WNT5A interactome, supporting their role in skeletal development. In addition to confirming that clustered -1 frameshifting variants in DVL1 and DVL3 are the main contributors to dominant Robinow syndrome, we also found likely pathogenic variants in candidate genes GPC4 and RAC3, both linked to the Wnt signaling pathway. These data support an initial hypothesis that Robinow syndrome results from perturbation of the Wnt/PCP pathway, suggest specific relevant domains of the proteins involved, and reveal key contributors in this signaling cascade during human embryonic development. Contrary to the view that non-allelic genetic heterogeneity hampers gene discovery, this study demonstrates the utility of rare disease genomic studies to parse gene function in human developmental pathways.

Foramina parietalia permagna: familial and radiological evaluation of two cases and review of literature.

PURPOSE: Foramina parietalia permagna is a variable intramembranous ossification defect of the parietal bones. Foramina parietalia permagna have an autosomal dominant inheritance, and it is showed that mutations in chromosome 5 and 11 are causing this anomaly. Enlarged parietal foramina occurs extremely rare. They are usually asymptomatic, but occasional headache, vomiting, pain over unprotected cerebral cortex, and seizures may be experienced by the patients. In the literature, some associated congenital bony defects, soft tissue pathologies, underlying neuronal deficits, and vascular variations have been described. METHODS: We report two cases of foramina parietal permagna with their pedigrees and genetic analysis. RESULTS: In case 1, cytogenetic analysis revealed a mutation of the ALX4 gene and all of the members of the family diagnosed with FPP. MRI revealed inferior vermian cerebellar hypoplasia. Surgery was not considered. In case 2, cytogenetic analysis could not be obtained because of financial reasons. Cranial MRI revealed hypoplastic right transverse sinus and sigmoid sinus, with a persistent parafalcine sinus. Surgery was not considered. CONCLUSION: Despite of its rarity, genetic background and some important associated anomalies make foramina parietalia permagna more than an uncommon insignificant genetic disorder.

How necessary is to analyze PTPN11 gene in fetuses with first trimester cystic hygroma and normal karyotype?

Cystic hygroma (CH) is a vascular-lymphatic malformation and can occur either as an isolated finding or as a part of a syndrome. The incidence of CH is about 1:1000-1:6000 births. Ultrasonographic diagnosis of CH is usually obtained in the first trimester, and the lesion can appear in septated or non-septated forms. Increased nuchal translucency and CH have been associated with a wide range of structural and genetic abnormalities. Most of CHs are associated with a number of chromosomal abnormalities especially Trisomy 21, 13, 18 and Turner syndrome. Besides, the associations between CH and non-chromosomal syndromes were also reported and Noonan Syndrome (NS) is one of the leading causes. Approximately 50% of NS cases are caused by mutations in the PTPN11 gene. A novel PTPN11 mutation defined in two separate fetuses with CH and associated with NS phenotype is being reported here.