X-linked Retinoschisis Associated with Retinitis Punctata Albescens Caused by a Mutation in the RS1 Gene: A Family Study

Purpose: To describe the clinical and genetic characteristics (mutation in RS1 gene) of a Spanish family with X-linked retinoschisis (XLRS) associated with retinitis punctata albescens (RPA). Methods: The detailed ophthalmological examination included best corrected visual acuity (BCVA), colour and autofluorescence photography, fluorescein angiography, optical coherence tomography and electrophysiology tests. A next-generation sequencing (NGS) strategy was applied to the index patient, and then sequenced in an Illumina NextSeq500 system. Candidate variants considered to be disease-causing in the patient were confirmed and segregated in the family by Sanger sequencing. Results: We have studied three siblings of 54, 59 and 50 years old. Two of them presented with macular foveoschisis and a whitish mottling of the pigment epithelium in the peripheral and equatorial retina, while the other had macular atrophy. Electroretinography revealed a reduced b-wave, while a-wave remained unchanged. Mutation in RS1 (c.98G>A; p.Trp33*) was identified as the cause of the disease. Conclusion: XLRS is a genetic disease that leads to irreversible visual loss. We describe an unusual phenotype manifestation of a known mutation.

An unusual phenotype occurs in 15% of mismatch repair-deficient tumors and is associated with non-colorectal cancers and genetic syndromes

Immunohistochemistry (IHC) and/or MSI-PCR (microsatellite instability-polymerase chain reaction) tests are performed routinely to detect mismatch repair deficiency (MMR-D). Classical MMR-D tumors present a loss of MLH1/PMS2 or MSH2/MSH6 with MSI-High. Other profiles of MMR-D tumors have been described but have been rarely studied. In this study, we established a classification of unusual MMR-D tumors and determined their frequency and clinical impact. All MMR-D tumors identified between 2007 and 2017 were selected. Any profile besides the classical MMR-D phenotype was defined as unusual. For patients with unusual MMR-D tumors, IHC, and PCR data were reviewed, the tumor mutation burden (TMB) was evaluated and clinical and genetic features were collected. Of the 4948 cases of MMR testing, 3800 had both the available IHC and MSI-PCR results and 585 of these had MMR-D. After reviewing the IHC and PCR, 21% of the cases initially identified as unusual MMR-D were reclassified, which resulted in a final identification of 89 unusual MMR-D tumors (15%). Unusual MMR-D tumors were more often associated with non-CRC than classical MMR-D tumors. Unusual MMR-D tumors were classified into four sub-groups: i) isolated loss of PMS2 or MSH6, ii) classical loss of MLH1/PMS2 or MSH2/MSH6 without MSI, iii) four MMR proteins retained with MSI and, iv) complex loss of MMR proteins, with clinical characteristics for each sub-group. TMB-high or -intermediate was shown in 96% of the cancers studied (24/25), which confirmed MMR deficiency. Genetic syndromes were identified in 44.9% (40/89) and 21.4% (106/496) of patients with unusual and classical MMR-D tumors, respectively (P < 0.001). Five patients treated with an immune checkpoint inhibitor (ICI) had a prolonged clinical benefit. Our classification of unusual MMR-D phenotype helps to identify MMR deficiency. Unusual MMR-D phenotype occurs in 15% of MMR-D tumors. A high frequency of genetic syndromes was noted in these patients who could benefit from ICI.

Novel mutation in the MYH2 gene in a symptomatic neonate with a hereditary myosin myopathy

INTRODUCTION: Hereditary myosin myopathies are muscle disorders caused by mutations in myosin heavy chain genes. The MYH2 gene encodes the fast 2A skeletal muscle isoform, and mutations manifest as joint contractures, muscle weakness, and external ophthalmoplegia. Muscle biopsy shows decreased type 2A fibers, and vacuoles are sometimes present in adults with progressive disease. PRESENTATION OF CASE: This case describes a full term baby boy with hypotonia, dysmorphic features, dysphagia, and aspiration. Whole genome sequencing detected a novel heterozygous variant in the MYH2 gene. Muscle biopsy showed decreased type 2A fibers and vacuoles in myofibers. DISCUSSION: Hypotonia and dysphagia are common in infants with a MYH2 myopathy. However, dysmorphic features and vacuoles on biopsy have not previous been described in infants with MYH2 myopathies. CONCLUSION: This case reports an unusual phenotype of a rare neonatal-onset congenital myopathy associated with a novel heterozygous variant in MYH2.

Lipid droplets regulate actin remodeling via prostaglandin signaling during Drosophila oogenesis

To ensure fertility, it is paramount to understand the factors controlling oocyte quality. One incompletely characterized factor contributing to oocyte quality is lipids. In somatic cells, a key regulator of lipid metabolism is lipid droplets (LDs), the sites of intracellular fat storage. Yet the role of LDs in fertility is poorly understood. Here we use Drosophila oogenesis as a model for uncovering if and how LDs promote egg development. LD accumulation in nurse cells coincides with dynamic actin remodeling necessary for late-stage follicle morphogenesis and fertility. Loss of major LD proteins, including PLIN2, Jabba, and ATGL, disrupts both actin bundle formation and cortical actin integrity; this unusual phenotype is also seen when Pxt, the enzyme responsible for prostaglandin (PG) synthesis, is missing. Further, both pharmacologic and genetic loss of PG synthesis or loss of PLIN2 or Jabba impairs intracellular LD dispersal. These similar phenotypes suggest that PGs and LD proteins act in the same pathway. Dominant genetic interaction studies indicate that there are three actin regulatory pathways: PLIN2 regulates actin remodeling independent of PG signaling, whereas Jabba and ATGL act in two separate PG-dependent pathways to regulate actin remodeling. We find that neither Jabba nor ATGL modulate the levels of Pxt or its localization to the endoplasmic reticulum. As ATGL is a triglyceride lipase, we hypothesize that it may release arachidonic acid (AA), the substrate for PG production, from triglycerides stored in LDs. Indeed, lipidomic analysis reveals the presence of AA-containing triglycerides in ovaries. In addition, exogenous AA is toxic and reduction of ATGL ameliorates toxicity; these observations suggest that ATGL indeed generates free AA. Our studies provide the first evidence that LDs and their associated proteins regulate PG signaling to control actin remodeling. In particular, we propose that ATGL releases AA from LDs to drive PG synthesis necessary for follicle development. We speculate that the same pathways are conserved across organisms to regulate oocyte development and promote fertility.

Impaired Ca2+ Sensitivity of a Novel GCAP1 Variant Causes Cone Dystrophy and Leads to Abnormal Synaptic Transmission Between Photoreceptors and Bipolar Cells

Guanylate cyclase-activating protein 1 (GCAP1) is involved in the shutdown of the phototransduction cascade by regulating the enzymatic activity of retinal guanylate cyclase via a Ca2+/cGMP negative feedback. While the phototransduction-associated role of GCAP1 in the photoreceptor outer segment is widely established, its implication in synaptic transmission to downstream neurons remains to be clarified. Here, we present clinical and biochemical data on a novel isolate GCAP1 variant leading to a double amino acid substitution (p.N104K and p.G105R) and associated with cone dystrophy (COD) with an unusual phenotype. Severe alterations of the electroretinogram were observed under both scotopic and photopic conditions, with a negative pattern and abnormally attenuated b-wave component. The biochemical and biophysical analysis of the heterologously expressed N104K-G105R variant corroborated by molecular dynamics simulations highlighted a severely compromised Ca2+-sensitivity, accompanied by minor structural and stability alterations. Such differences reflected on the dysregulation of both guanylate cyclase isoforms (RetGC1 and RetGC2), resulting in the constitutive activation of both enzymes at physiological levels of Ca2+. As observed with other GCAP1-associated COD, perturbation of the homeostasis of Ca2+ and cGMP may lead to the toxic accumulation of second messengers, ultimately triggering cell death. However, the abnormal electroretinogram recorded in this patient also suggested that the dysregulation of the GCAP1–cyclase complex further propagates to the synaptic terminal, thereby altering the ON-pathway related to the b-wave generation. In conclusion, the pathological phenotype may rise from a combination of second messengers’ accumulation and dysfunctional synaptic communication with bipolar cells, whose molecular mechanisms remain to be clarified.

Exopolysaccharide anchoring creates an extreme resistance to sedimentation

By evolving strains of E. coli that hyper-resist sedimentation, we discovered an uncharacterized mechanism that bacteria can use to remain in suspension indefinitely without expending energy. This unusual phenotype was traced to the anchoring of long colanic acid polymers (CAP) that project from the cell surface. Although each characterized mutant activated this same mechanism, the genes responsible and the strengths of the phenotypes varied. Mutations in rcsC, lpp, igaA, or the yjbEFGH operon were sufficient to stimulate sedimentation resistance, while mutations altering the cps promoter, cdgI, or yjbF provided phenotypic enhancements. The sedimentation resistances changed in response to temperature, growth phase, and carbon source and each mutant exhibited significantly reduced biofilm formation. We discovered that the degree of colony mucoidy exhibited by these mutants was not related to the degree of Rcs pathways activation or to the amount of CAP that was produced; rather, it was related to the fraction of CAP that was shed as a true exopolysaccharide. Therefore, these and other mutations that activate this phenotype are likely to be absent from genetic screens that relied on centrifugation to harvest bacteria. We also found that this anchored CAP form is not linked to LPS cores and may not be attached to the outer membrane. IMPORTANCE Bacteria can partition in aqueous environments between surface-dwelling, planktonic, sedimentary, and biofilm forms. Residence in each location provides an advantage depending on nutritional and environmental stresses and a community of a single species is often observed to be distributed throughout two or more of these niches. Another adaptive strategy is to produce an extracellular capsule, which provides an environmental shield for the microbe and can allow escape from predators and immune systems. We discovered that bacteria can either shed or stably anchor capsules to dramatically alter their propensity to sediment. The degree to which the bacteria anchor their capsule is controlled by a stress sensing system, suggesting that anchoring may be used as an adaptive response to severe environmental challenges.

Differential levels of IFNα subtypes in autoimmunity and viral infection

Type I interferons are essential for host response to viral infections, while dysregulation of their response can result in autoinflammation or autoimmunity. Among IFNα (alpha) responses, 13 subtypes exist that signal through the same receptor, but have been reported to have different effector functions. However, the lack of available tools for discriminating these closely related subtypes, in particular at the protein level, has restricted the study of their differential roles in disease. We developed a digital ELISA with specificity and high sensitivity for the IFNα2 subtype. Application of this assay, in parallel with our previously described pan-IFNα assay, allowed us to study different IFNα protein responses following cellular stimulation and in diverse patient cohorts. We observed different ratios of IFNα protein responses between viral infection and autoimmune patients. This analysis also revealed a small percentage of autoimmune patients with high IFNα2 protein measurements but low pan-IFNα measurements. Correlation with an ISG score and functional activity showed that in this small sub group of patients, IFNα2 protein measurements did not reflect its biological activity. This unusual phenotype was partly explained by the presence of anti-IFNα auto-antibodies in a subset of autoimmune patients. This study reports ultrasensitive assays for the study of IFNα proteins in patient samples and highlights the insights that can be obtained from the use of multiple phenotypic readouts in translational and clinical studies.

An Unusual Phenotype in Dutch Patients With Oculocutaneous Albinism Type 4: Evident Hypopigmentation Without Other Ocular Deficits.

Purpose: To describe the phenotype of Dutch patients with oculocutaneous albinism type 4 (OCA4).Patients and Methods: We collected data on pigmentation (skin, hair, and eyes), visual acuity (VA), nystagmus, foveal hypoplasia, chiasmal misrouting, and molecular analyses of nine Dutch OCA4 patients from the Bartiméus Diagnostic Center for complex visual disorders.Results: All patients had severely reduced pigmentation of skin, hair, and eyes with iris transillumination over 360 degrees. Three unrelated OCA4 patients had normal VA, no nystagmus, no foveal hypoplasia, and no misrouting of the visual pathways. Six patients had poor visual acuity (0.6 to 1.0 logMAR), nystagmus, severe foveal hypoplasia and misrouting. We found two novel mutations in the SLC45A2 gene, c.310C>T; p.(Pro104Ser), and c.1368+3_1368+9del p.(?).Discussion: OCA4 patients of this Dutch cohort all had hypopigmentation of skin, hair, and iris translucency. However, patients were either severely affected with regard to visual acuity, foveal hypoplasia, and misrouting, or visually not affected at all. We describe for the first time OCA4 patients with an evident lack of pigmentation, but normal visual acuity, normal foveal development and absence of misrouting. This implies that absence of melanin does not invariably lead to foveal hypoplasia and abnormal routing of the visual pathways.