In pleiotropic diseases, multiple organ systems are affected causing a variety of clinical manifestations. Here, we report a pleiotropic disorder with a unique constellation of neurological, endocrine, exocrine, and haematological findings that is caused by biallelic MADD variants. MADD, the mitogen-activated protein kinase (MAPK) activating death domain protein, regulates various cellular functions, such as vesicle trafficking, activity of the Rab3 and Rab27 small GTPases, tumour necrosis factor-α (TNF-α)-induced signalling and prevention of cell death. Through national collaboration and GeneMatcher, we collected 23 patients with 21 different pathogenic MADD variants identified by next-generation sequencing. We clinically evaluated the series of patients and categorized the phenotypes in two groups. Group 1 consists of 14 patients with severe developmental delay, endo- and exocrine dysfunction, impairment of the sensory and autonomic nervous system, and haematological anomalies. The clinical course during the first years of life can be potentially fatal. The nine patients in Group 2 have a predominant neurological phenotype comprising mild-to-severe developmental delay, hypotonia, speech impairment, and seizures. Analysis of mRNA revealed multiple aberrant MADD transcripts in two patient-derived fibroblast cell lines. Relative quantification of MADD mRNA and protein in fibroblasts of five affected individuals showed a drastic reduction or loss of MADD. We conducted functional tests to determine the impact of the variants on different pathways. Treatment of patient-derived fibroblasts with TNF-α resulted in reduced phosphorylation of the extracellular signal-regulated kinases 1 and 2, enhanced activation of the pro-apoptotic enzymes caspase-3 and -7 and increased apoptosis compared to control cells. We analysed internalization of epidermal growth factor in patient cells and identified a defect in endocytosis of epidermal growth factor. We conclude that MADD deficiency underlies multiple cellular defects that can be attributed to alterations of TNF-α-dependent signalling pathways and defects in vesicular trafficking. Our data highlight the multifaceted role of MADD as a signalling molecule in different organs and reveal its physiological role in regulating the function of the sensory and autonomic nervous system and endo- and exocrine glands.

中文翻译：

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双等位基因 MADD 变异会导致从发育迟缓到多系统疾病的表型谱。


在多效性疾病中，多个器官系统受到影响，导致多种临床表现。在此，我们报告了一种由双等位基因MADD变异引起的多效性疾病，具有一系列独特的神经学、内分泌、外分泌和血液学发现。 MADD 是丝裂原激活蛋白激酶 (MAPK) 激活死亡结构域蛋白，调节各种细胞功能，例如囊泡运输、Rab3 和 Rab27 小 GTP 酶的活性、肿瘤坏死因子-α (TNF-α) 诱导的信号转导和预防细胞死亡。通过国家合作和 GeneMatcher，我们收集了 23 名患者，这些患者具有通过下一代测序鉴定出的 21 种不同的致病性MADD变异。我们对这一系列患者进行了临床评估，并将表型分为两组。第 1 组由 14 名患有严重发育迟缓、内分泌和外分泌功能障碍、感觉和自主神经系统损伤以及血液学异常的患者组成。生命最初几年的临床病程可能是致命的。第 2 组的 9 名患者具有主要的神经表型，包括轻度至重度发育迟缓、肌张力低下、言语障碍和癫痫发作。 mRNA 分析揭示了两种患者来源的成纤维细胞系中存在多个异常的MADD转录本。对 5 名受影响个体的成纤维细胞中 MADD mRNA 和蛋白质的相对定量显示，MADD 急剧减少或消失。我们进行了功能测试，以确定变异对不同途径的影响。 与对照细胞相比，用 TNF-α 处理患者来源的成纤维细胞可减少细胞外信号调节激酶 1 和 2 的磷酸化，增强促凋亡酶 caspase-3 和 -7 的激活，并增加细胞凋亡。我们分析了患者细胞中表皮生长因子的内化，并发现了表皮生长因子内吞作用的缺陷。我们得出的结论是，MADD 缺陷是多种细胞缺陷的基础，这些缺陷可归因于 TNF-α 依赖性信号通路的改变和囊泡运输的缺陷。我们的数据强调了 MADD 作为信号分子在不同器官中的多方面作用，并揭示了其在调节感觉和自主神经系统以及内分泌腺和外分泌腺功能中的生理作用。