Dominant missense variants in SREBF2 are associated with complex dermatological, neurological, and skeletal abnormalities.

PURPOSE: We identified 2 individuals with de novo variants in SREBF2 that disrupt a conserved site 1 protease (S1P) cleavage motif required for processing SREBP2 into its mature transcription factor. These individuals exhibit complex phenotypic manifestations that partially overlap with sterol regulatory element binding proteins (SREBP) pathway-related disease phenotypes, but SREBF2-related disease has not been previously reported. Thus, we set out to assess the effects of SREBF2 variants on SREBP pathway activation. METHODS: We undertook ultrastructure and gene expression analyses using fibroblasts from an affected individual and utilized a fly model of lipid droplet (LD) formation to investigate the consequences of SREBF2 variants on SREBP pathway function. RESULTS: We observed reduced LD formation, endoplasmic reticulum expansion, accumulation of aberrant lysosomes, and deficits in SREBP2 target gene expression in fibroblasts from an affected individual, indicating that the SREBF2 variant inhibits SREBP pathway activation. Using our fly model, we discovered that SREBF2 variants fail to induce LD production and act in a dominant-negative manner, which can be rescued by overexpression of S1P. CONCLUSION: Taken together, these data reveal a mechanism by which SREBF2 pathogenic variants that disrupt the S1P cleavage motif cause disease via dominant-negative antagonism of S1P, limiting the cleavage of S1P targets, including SREBP1 and SREBP2.

Recurrent p.H119Y variant in MAP2K1 expands the phenotypic spectrum of MAP2K1-related RASopathy.

We report three unrelated individuals with atypical clinical findings for cardio-facio-cutaneous (CFC) syndrome, all of whom have the same novel, heterozygous de novo p.H119Y (c.355 C>T) transition variant in MAP2K1, identified by exome sequencing. MAP2K1 encodes MEK1, dual specificity mitogen-activated protein kinase kinase 1, and is one of four genes in the canonical RAS/MAPK signal transduction pathway associated with CFC syndrome. The p.H119Y variant is a non-conservative amino acid substitution that is predicted to impact the tertiary protein structure, and it occurs at a position in the protein kinase domain of MAP2K1 that is highly conserved across species. The clinical findings in these three individuals include facial features that are nonclassical for CFC syndrome, extremely poor weight gain, absence of congenital cardiac defects or cardiomyopathy, normal cognition or only mild intellectual disabilities, normal hair, mild skin abnormalities, and consistent behavioral features of anxiety, photophobia, and sensory hypersensitivities. These individuals expand the phenotypic spectrum of MAP2K1-related RASopathy.

Using a new analytic approach for genotyping and phenotyping chromosome 9p deletion syndrome.

Using a new analytic method ("unique non-overlapping region" (UNOR) analysis), we characterized the genotypes and phenotypes of a large cohort of individuals diagnosed with chromosome 9p deletion syndrome (9PMS) and defined critical genomic regions. We extracted phenotypic information from 48 individuals with 9PMS from medical records and used a guided interview with caregivers to clarify ambiguities. Using high-resolution whole-genome sequencing for breakpoint definition, we aligned deletions and drew virtual breakpoints to obtain UNORs associated with phenotypic characteristics. We next extracted genotype and phenotype data for 57 individuals identified from a systematic review of the 9PMS literature and analyzed these as above. Common phenotypic features included developmental delay/intellectual disability, dysmorphic features, hypotonia, genital defects in XY individuals, psychiatric diagnoses, chronic constipation, atopic disease, vision problems, autism spectrum disorder, gastroesophageal reflux disease, trigonocephaly, congenital heart disease, and neonatal hypoglycemia. Our approach confirmed previous literature reports of an association of FREM1 with trigonocephaly and suggested a possible modifier element for this phenotype. In conclusion, the UNOR approach delineated phenotypic characteristics for 9PMS and confirmed the critical role of FREM1 and a possible long-distance regulatory element in pathogenesis of trigonocephaly that will need to be replicated in future studies.

Human pluripotent stem cell modeling of alveolar type 2 cell dysfunction caused by ABCA3 mutations.

Mutations in ATP-binding cassette A3 (ABCA3), a phospholipid transporter critical for surfactant homeostasis in pulmonary alveolar type II epithelial cells (AEC2s), are the most common genetic causes of childhood interstitial lung disease (chILD). Treatments for patients with pathological variants of ABCA3 mutations are limited, in part due to a lack of understanding of disease pathogenesis resulting from an inability to access primary AEC2s from affected children. Here, we report the generation of AEC2s from affected patient induced pluripotent stem cells (iPSCs) carrying homozygous versions of multiple ABCA3 mutations. We generated syngeneic CRISPR/Cas9 gene-corrected and uncorrected iPSCs and ABCA3-mutant knockin ABCA3:GFP fusion reporter lines for in vitro disease modeling. We observed an expected decreased capacity for surfactant secretion in ABCA3-mutant iPSC-derived AEC2s (iAEC2s), but we also found an unexpected epithelial-intrinsic aberrant phenotype in mutant iAEC2s, presenting as diminished progenitor potential, increased NFκB signaling, and the production of pro-inflammatory cytokines. The ABCA3:GFP fusion reporter permitted mutant-specific, quantifiable characterization of lamellar body size and ABCA3 protein trafficking, functional features that are perturbed depending on ABCA3 mutation type. Our disease model provides a platform for understanding ABCA3 mutation-mediated mechanisms of alveolar epithelial cell dysfunction that may trigger chILD pathogenesis.