目的　总结PIK3CA基因突变致巨脑毛细血管畸形多小脑回综合征（MCAP）的临床特征。方法　回顾分析 1例PIK3CA基因错义突变致MCAP患儿的临床表型、影像学检查结果和随访情况，并复习相关文献。结果　患儿，女， 4 岁2个月，只会叫爸妈，能理解简单指令，行走步态欠稳，易摔跤。头围56.9 cm，腭弓高，左耳廓有一窦道，左侧肢体较右 侧肥大，下肢关节过度伸展，肌张力低，肌力Ⅳ级。Gessell评估发育商32。头颅磁共振成像示Chiari畸形Ⅰ型，伴梗阻性脑 积水。外显子高通量测序结果显示，PIK3CA基因存在错义变异c.1133G＞A，p.Cys378Tyr（杂合） ，为新生突变，患儿父 母此位点均为正常基因型。随访患儿至5岁1个月，能说3~4个字短句，能进行简单语言交流，仍行走不稳，易摔跤，头围 57.7 cm。结论　发现1例PIK3CA基因新发突变所致MCAP，丰富了PIK3CA基因突变谱。

Objective　To explore the clinical features of Megalencephaly-capillary malformation-polymicrogyria syndrome (MCAP) caused by PIK3CA gene mutation. Method　The clinical phenotype, imaging findings and follow-up of MCAP caused by missense mutation of PIK3CA gene in a child were retrospectively analyzed, and the related literature was reviewed. Results　A girl aged 4 years and 2 months can only say ma, pa and understand simple instructions. She had unsteady walking gait and was easy to fall. The child had a head circumference of 56.9 cm, a high palatal arch, and a sinus tract in the left auricle. The left limb was more hypertrophic than the right side and the lower limb joints were over-extended. She had low muscle tension and the muscle strength was grade IV. Gessell development scales showed the development quotient was 32. Cranial magnetic resonance imaging showed type I chiari malformation with obstructive hydrocephalus. High-throughput exon sequencing results showed that PIK3CA gene had a "missense mutation of c.1133G>A, p.Cys378Tyr (heterozygous)", which was a new mutation. The parents of the children had normal genotypes. The child was followed up to the age of 5 years and 1 month. She could speak short sentences of 3-4 words and communicate in simple language. She was still unsteady in walking and easy to fall, with a head circumference of 57.7 cm. Conclusion　A case of MCAP caused by a new mutation of PIK3CA gene was found, which enriched the mutation spectrum of PIK3CA gene.