Objective: To summarize and analyze of the clinical and genetic characteristics of children with nonmuscle myosin heavy chain 9 (MYH9)-related disease (MYH9-RD). Methods: To screen the patients who were first diagnosed as "chronic/refractory immune thrombocytopenia (ITP) " from April 2016 to May 2019 in Beijing Children's Hospital by genetic and clinical examinations, then the clinical manifestation, laboratory examination and genetics results of 7 children diagnosed with MYH9-RD were collected and summarized retrospectively. Results: Among 7 children diagnosed with MYH9-RD, 3 were males and 4 females. The age of onset was 1.25 (0.41-6.16) years. The course of disease was 2.16 (0.41-8.59) years. The automatic platelet count was (9 (5-30))×109/L. All the cases were found with giant platelets under microscope,and the manual platelet count was (70 (30-100))×109/L. Four cases had skin hemorrhage or epistaxis and 3 cases had no bleeding. All 7 patients had received first-or second-line therapy of ITP, of whom 1 case received splenic embolization, and all the treatments mentioned above were ineffective. Finally, it was confirmed that all 7 patients had heterozygous missense mutations of MYH9 gene by next generation sequencing (NGS), including 2 pedigrees and 5 sporadic cases. Four sporadic mutations occurred in N-terminal globular head domain (HD), and 1 sporadic case with p.D1424N mutations occurred in the C-terminal tail domain (TD). One of the pedigrees also had p.D1424N mutation. The other familial case had a novel variant with one missense variant p.A44D caused by the c.131C>A transition. One of the two p.R702 mutations had kidney damage, and several relatives of the new p.A44D mutations had deafness. Conclusions: In this study, the spontaneous mutations of seven MYH9-RD were common, and all patients were misdiagnosed as ITP, whereas the bleeding was mild and immunotherapy was ineffective. The suspected disease can be identified earlier by manual visual platelet volume and count, which can be confirmed by genetic testing. It is more important to monitor the development of other organs damage instead of thrombocytopenia. For cases with p.R702 mutations the doctor should be aware of kidney damage, and for the cases with novel mutations p.A44D the doctor should be aware of hearing loss.
目的： 总结分析儿童非肌性肌球蛋白重链9相关疾病（MYH9-RD）的临床特征及遗传学特点，提高该类疾病的早期诊断。 方法： 通过基因和临床相关指标对2016年4月到2019年5月于首都医科大学附属北京儿童医院血液病中心“慢性、难治性免疫性血小板减少症”住院患儿进行筛查，对最终确诊为MYH9-RD的7例患儿的临床表现、实验室检查、遗传学等结果进行回顾性总结。 结果： 7例患儿中男3例、女4例；发病年龄1.25（0.41~6.16）岁；病程2.16（0.41~8.59）年；机测血小板计数［9（5~30）］×109/L，人工显微镜下7例患儿血小板体积均偏大，且同期血小板计数［70（30~100）］×109/L。4例伴皮肤出血点及鼻衄，3例无出血表现。7例均曾予免疫性血小板减少症（ITP）一线或二线免疫治疗，其中1例行脾栓塞术，上述治疗均无效，最终经二代测序证实MYH9基因均存在杂合错义突变，其中5例新发突变、2例家系突变。4例新发突变发生于N端球状头部，1例新发突变发生于尾部卷曲螺旋结构域，为p.D1424N突变。1例家系病例也为p.D1424N，另1例家系病例突变为p.A44D，为MYH9基因新的突变位点。2例p.R702突变中1例已经出现肾功能损伤，p.A44D突变病例患儿多名亲属存在耳聋。 结论： 本组7例MYH9-RD患儿新发突变多见，均被误诊为ITP，但其出血表现轻、对免疫治疗无效。对可疑病例通过人工目测血小板体积及计数可早期识别，基因检测可证实。该类疾病需加强监测除血小板减少外的器官损伤发生发展，其中2例发生在p.R702的突变需警惕肾脏损伤，p.A44D新的突变位点需注意监测听力。.