■SAMD9基因的杂合从头变异导致复杂的多系统疾病,MIRAGE综合征.患者的特征是骨髓增生异常,感染,生长限制,肾上腺功能不全,性腺功能障碍和肠病。SAMD9中的致病变异是获得功能并增强其作为生长抑制物的作用,导致许多组织的生长受限。两项研究报道了MIRAGE患者皮肤成纤维细胞的变化,更具体地识别扩大的内体。我们以前也显示了与对照组相比,患者成纤维细胞内体大小的细微变化。然而,内体的这些变异并不像文献中描述的那样显著.
我们使用透射电子显微镜(TEM)对来自三名患者成纤维细胞的大量细胞进行了观察性研究,以评估与对照图像相比的超微结构形态。
■在所有患者样品的细胞器中观察到一致的变化。特别是,检测到内体活性增加,以胞吞增多和囊泡出芽为特征,内体数量增加,以及大型溶酶体和核内体。内质网也很突出。线粒体在选定的细胞中出现肿大,可能是由于细胞压力。与对照相比,细胞核没有显示出主要差异。
■TEM是研究组织和细胞器形态特征的强大工具,虽然TEM数据可能会受到样品制备方法的影响,因此,有可能解释独立研究之间的差异,其分析可以依赖于研究者的经验。我们在患者成纤维细胞中观察到的内体活性增加可能表明SAMD9调节受体的内吞作用,充当核内融合促进者,或溶酶体激活。然而,SAMD9调节细胞生长的确切机制仍未完全了解,需要进一步的研究来阐明其致病途径并开发治疗方法来支持患者。
UNASSIGNED: Heterozygous de novo variants in the gene
SAMD9 cause the complex multisystem disorder, MIRAGE syndrome. Patients are characterised by myelodysplasia, infections, growth restriction, adrenal insufficiency, gonadal dysfunction and enteropathies. Pathogenic variants in
SAMD9 are gain-of-function and enhance its role as a growth repressor, leading to growth restriction of many tissues. Two studies have reported changes in skin fibroblasts derived from MIRAGE patients, more specifically identifying enlarged endosomes. We have also previously shown subtle changes in endosome size in patients\' fibroblasts compared to controls. However, these variations in endosomes were not as marked as those described in the literature.
UNASSIGNED: We have performed an observational study using transmission electron microscopy (TEM) in a larger number of cells derived from three patients\' fibroblasts to assess ultrastructure morphology compared to control images.
UNASSIGNED: Consistent changes were observed in cell organelles in all patient samples. In particular, increased endosomal activity was detected, characterised by augmented pinocytosis and vesicle budding, increased endosome number, as well as by large lysosomes and endosomes. Endoplasmic reticulum was also prominent. Mitochondria appeared enlarged in selected cells, possibly due to cellular stress. Cell nuclei did not display major differences compared to controls.
UNASSIGNED: TEM is a powerful tool to investigate morphological features of tissues and cell organelles, although TEM data could be affected by sample preparation methodology, therefore potentially explaining the variability between independent studies, and its analysis can be dependent on the experience of the researcher. The increased endosomal activity we have observed in patients\' fibroblasts could indicate that
SAMD9 regulates endocytosis of receptors, acting as an endosome fusion facilitator, or in lysosomal activation. However, the precise mechanism(s) by which
SAMD9 regulates cell growth is still not fully understood, and further studies are needed to elucidate its pathogenic pathway and develop therapeutic approaches to support patients.