患儿1，男，3岁6个月，因喂养困难，运动发育落后就诊，生后反应稍差，哭声低弱，智力和运动发育落后，平素抵抗力差，反复呼吸道感染，四肢肌张力低下，有特殊面容（耳位低、双下颌、高腭弓），右手通贯掌，基因检测提示SMARCB1基因存在c.1096C>T杂合变异。患儿2，男，3岁，因发育迟滞伴有特殊面容就诊，基因检测发现与患儿1存在相同的致病基因突变。2例患儿无亲缘关系，经临床表现及基因检测证实2例患儿均为Coffin-Siris综合征3型。Coffin-Siris综合征是一种罕见的遗传病，尽早完善遗传学检测可协助诊断。

Patient 1, a 3-year-6-month-old male, presented with feeding difficulties and delayed motor development. He exhibited poor responsiveness at birth, weak crying, intellectual and motor delays, low immunity, recurrent respiratory infections, hypotonia of the limbs, and distinctive facial features (low-set ears, double chin, and high arched palate), as well as a single transverse palmar crease on the right hand. Genetic testing revealed a c.1096C>T heterozygous variant in the SMARCB1 gene. Patient 2, a 3-year-old male, presented with developmental delay and distinctive facial features. Genetic testing identified the same pathogenic mutation as in Patient 1. The two patients are unrelated, and clinical phenotyping and genetic testing confirmed both cases as Coffin-Siris syndrome type 3. Coffin-Siris syndrome is a rare genetic disorder, and early genetic testing can aid in diagnosis.