KBG 증후군은 특징적인 얼굴 기형 및 발달 장애, 저 신장 등을 보이는 희귀한 질환이며, ANKRD11유전자의 변이가 KBG 증후군을 일으킨다고 알려져 있다. 그 임상 양상의 스펙트럼은 넓은 편이며, 발달장애와 신경학적 이상의 경우 개인마다 다양한 정도로 보고되고 있다. 본 증례의 환자들 역시 서로 다른 정도의 발달 장애를 보였으며, 그 중 더 심한 정도의 발달 장애를 가진 환자에서는 뇌전증이 동반되었다. 기존의 KBG증후군의 진단 기준에서 macrodontia는 매우 중요한 요소였으며, 대부분의 KBG 증후군 환자에서 나타난다고 보고되었다. 본 증례의 환자들은 발달장애를 보여 시행한 diagnostic exome sequencing을 통해 ANKRD11 유전자 이상을 확인하였지만 macrodontia는 관찰되지 않았다. 이는 KBG 증후군이 현재까지 밝
혀진 것 보다 더 흔할 수 있으며, 특징적인 얼굴 기형이 없는 경우에도 발달장애가 있는 환자들에서는 더욱 적극적인 유전자 검사를 시행하여 KBG 증후군을 진단 할 필요가 있음을 시사한다.

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KBG syndrome is a rare neurodevelopmental disorder characterized by intellectual disability, skeletal anomalies, short stature, craniofacial dysmorphism, and macrodontia. ANKRD11 gene mutation and 16q24.3 microdeletion have been reported to cause KBG syndrome. Here, we report two patients with ANKRD11 mutations who initially presented with neurologic symptoms such as developmental delay and seizures. Patient 1 was a 23-month-old boy who presented with a global developmental delay. Language delay was the most dominant feature. He had hypertelorism, hearing impairment, and behavior problems characterized as hyperactivity. A c.1903_1907delAAACA (p.Lys635GInfsTer26) mutation in ANKRD11 was identified with diagnostic exome sequencing. Patient 2 was a 14-month-old boy with developmental delay and seizure. He also had atrial septum defect, and ventricular septal defect. Generalized tonic seizures began at the age of 8 months. Electroencephalography showed generalized sharp and slow wave pattern. Seizures did not respond to antiepileptic drugs. A loss of function mutation c.5350_5351delTC (p.ser1784HisfsTer12) in ANKRD11 was identified with diagnostic exome sequencing. In both cases, characteristic features of KBG syndrome such as short stature or macrodontia, were absent, and they visited the hospital due to neurological symptoms. These findings suggest that more patients with mild phenotypes of KBG syndrome are being recognized with advances in diagnostic exome sequencing genetic technologies.

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