Integrative analysis of Lunatic Fringe variants associated with spondylocostal dysostosis type-III.

Lunatic Fringe (LFNG) is required for spinal development. Biallelic pathogenic variants cause spondylocostal dysostosis type-III (SCD3), a rare disease generally characterized by malformed, asymmetrical, and attenuated development of the vertebral column and ribs. However, a variety of SCD3 cases reported have presented with additional features such as auditory alterations and digit abnormalities. There has yet to be a single, comprehensive, functional evaluation of causative LFNG variants and such analyses could unveil molecular mechanisms for phenotypic variability in SCD3. Therefore, nine LFNG missense variants associated with SCD3, c.564C>A, c.583T>C, c.842C>A, c.467T>G, c.856C>T, c.601G>A, c.446C>T, c.521G>A, and c.766G>A, were assessed in vitro for subcellular localization and protein processing. Glycosyltransferase activity was quantified for the first time in the c.583T>C, c.842C>A, and c.446C>T variants. Primarily, our results are the first to satisfy American College of Medical Genetics and Genomics PS3 criteria (functional evidence via well-established assay) for the pathogenicity of c.583T>C, c.842C>A, and c.446C>T, and replicate this evidence for the remaining six variants. Secondly, this work indicates that all variants that prevent Golgi localization also lead to impaired protein processing. It appears that the FRINGE domain is responsible for this phenomenon. Thirdly, our data suggests that variant proximity to the catalytic residue may influence whether LFNG is improperly trafficked and/or enzymatically dysfunctional. Finally, the phenotype of the axial skeleton, but not elsewhere, may be modulated in a variant-specific fashion. More reports are needed to continue testing this hypothesis. We anticipate our data will be used as a basis for discussion of genotype-phenotype correlations in SCD3.

Direct Reprogramming of Fibroblasts to Osteoblasts: Techniques and Methodologies.

Direct reprogramming (DR) is an emerging technique that can be applied to convert fibroblasts into osteoblast-like cells, promoting bone formation and regeneration. We review the current methodology of DR in relation to the creation of induced osteoblasts, including a comparison of transcription factor-mediated reprogramming and nontranscription factor-mediated reprogramming. We review the selection of reprogramming factors and delivery systems required. Transcription factor cocktails, such as the RXOL cocktail (Runx2, Osx, OCT3/4, and L-MYC), have shown promise in inducing osteogenic differentiation in fibroblasts. Alterations to the original cocktail, such as the addition of Oct9 and N-myc, have resulted in improved reprogramming efficiency. Transcription factor delivery includes integrative and nonintegrative systems which encompass viral vectors and nonviral methods such as synthetic RNA. Recently, an integrative approach using self-replicating RNA has been developed to achieve a longer and more sustained transcription factor expression. Nontranscription factor-mediated reprogramming using small molecules, proteins, inhibitors, and agonists has also been explored. For example, IGFBP7 protein supplementation and ALK5i-II inhibitor treatment have shown potential in enhancing osteoblast reprogramming. Direct reprogramming methods hold great promise for advancing bone regeneration and tissue repair, providing a potential therapeutic approach for fracture healing and the repair of bone defects. Multiple obstacles and constraints need to be addressed before a clinically significant level of cell therapy will be reached. Further research is needed to optimize the efficiency of the reprogramming cocktails, delivery methods, and safety profile of the reprogramming process.

CYP26B1-related disorder: expanding the ends of the spectrum through clinical and molecular evidence.

CYP26B1 metabolizes retinoic acid in the developing embryo to regulate its levels. A limited number of individuals with pathogenic variants in CYP26B1 have been documented with a varied phenotypic spectrum, spanning from a severe manifestation involving skull anomalies, craniosynostosis, encephalocele, radio-humeral fusion, oligodactyly, and a narrow thorax, to a milder presentation characterized by craniosynostosis, restricted radio-humeral joint mobility, hearing loss, and intellectual disability. Here, we report two families with CYP26B1-related phenotypes and describe the data obtained from functional studies of the variants. Exome and Sanger sequencing were used for variant identification in family 1 and family 2, respectively. Family 1 reflects a mild phenotype, which includes craniofacial dysmorphism with brachycephaly (without craniosynostosis), arachnodactyly, reduced radioulnar joint movement, conductive hearing loss, learning disability-and compound heterozygous CYP26B1 variants: (p.[(Pro118Leu)];[(Arg234Gln)]) were found. In family 2, a stillborn fetus presented a lethal phenotype with spina bifida occulta, hydrocephalus, poor skeletal mineralization, synostosis, limb defects, and a synonymous homozygous variant in CYP26B1: c.1083C > A. A minigene assay revealed that the synonymous variant created a new splice site, removing part of exon 5 (p.Val361_Asp382del). Enzymatic activity was assessed using a luciferase assay, demonstrating a notable reduction in exogenous retinoic acid metabolism for the variant p.Val361_Asp382del. (~ 3.5 × decrease compared to wild-type); comparatively, the variants p.(Pro118Leu) and p.(Arg234Gln) demonstrated a partial loss of metabolism (1.7× and 2.3× reduction, respectively). A proximity-dependent biotin identification assay reaffirmed previously reported ER-resident protein interactions. Additional work into these interactions is critical to determine if CYP26B1 is involved with other biological events on the ER. Immunofluorescence assay suggests that mutant CYP26B1 is still localized in the endoplasmic reticulum. These results indicate that novel pathogenic variants in CYP26B1 result in varying levels of enzymatic activity that impact retinoic acid metabolism and relate to the distinct phenotypes observed.

Spondyloepimetaphyseal dysplasia with joint laxity type 2: Aggregating the literature and reporting on the life of a 66-year-old man.

Spondyloepimetaphyseal dysplasia with joint laxity, leptodactylic type (SEMDJL2), is a rare bone dysplasia that results from hotspot (amino acids148/149) mutations in KIF22. Clinically, affected individuals present with generalized joint laxity, limb malalignment, midface hypoplasia, gracile digits, postnatal short stature, and occasionally, tracheolaryngomalacia; additionally, radiological features include severe epi-metaphyseal abnormalities and slender metacarpals. This report evaluates the progression of SEMDJL2 throughout the life of the oldest individual reported in the literature-a 66-year-old man with a pathogenic KIF22 variant (c.443C > T, p.Pro148Leu). The proband developed many of the clinical and radiological alterations consistent with the presentation of other individuals in the literature. Interestingly, throughout his life, joint limitation progressed, beginning with knee and elbow stricture (year 20), and later, limitation of the shoulders, hips, ankles, and wrists (year 40). This differs from previous case reports, where joint limitation is identified in 1-to-2 joints. Cumulatively, the progressive body-wide joint limitation resulted in early retirement (year 45) and difficulty completing daily tasks and managing personal hygiene culminating in the need for assisted living (year 65). In conclusion, we report on the clinical and radiological developments of a 66-year-old man with SEMDJL2, that developed significant joint limitation in adulthood.