21q22 contains several dosage sensitive genes that are important in neurocognitive development. Determining impacts of gene dosage alterations in this region can be useful in establishing contributions of these genes to human development and disease. We describe a 15‐month‐old girl with a 1,140 kb homozygous deletion in the Down Syndrome Critical Region at 21q22.2 including 4 genes; B3GALT5, IGSF5, PCP4, DSCAM, and a microRNA (MIR4760). Clinical singleton genome sequencing did not report any candidate gene variants for the patient's phenotype. She presented with hypotonia, global developmental delay, cortical visual impairment, and mild facial dysmorphism. Ophthalmological exam was suggestive of retinopathy. We propose that the absence of DSCAM and PCP4 may contribute to the patient's neurological and retinal phenotype, while the role of absent B3GALT5 and IGSF5 in her presentation remain unclear at this time.

中文翻译：

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低渗，发育迟缓，皮层视力障碍和视网膜病变患者的21q22.2纯合缺失

21q22包含几个对神经认知发展很重要的剂量敏感基因。确定该区域中基因剂量变化的影响可能有助于确定这些基因对人类发育和疾病的贡献。我们描述了一个唐氏综合症关键区域在21q22.2处具有1140 kb纯合缺失的15个月大女孩，其中包括4个基因；B3GALT5，IGSF5，PCP4，DSCAM和microRNA（MIR4760）。临床单例基因组测序未报告患者表型的任何候选基因变异。她表现为肌张力低下，整体发育迟缓，皮质视觉障碍和轻度面部畸形。眼科检查提示视网膜病变。我们建议缺少DSCAM和PCP4可能有助于患者的神经和视网膜表型，但目前尚不清楚缺乏B3GALT5和IGSF5在其表现中的作用。