Identification of Mosaic Variants in Neurodevelopmental Disorders

Abstract

Neurodevelopmental disorders (NDDs) refer to a group of disorders that affect cognitive and social communicative development. Growing evidence indicates that mosaicism of genes can cause NDD, but detecting low level mosaic variants with an allele frequency <5% remains a challenge. The aim of this study was to prove, quantify, and characterize mosaic variants in NDD with DNA obtained from blood. We retrospectively reviewed patients with NDDs who underwent conventional NGS panel testing at Severance Children's Hospital from 2016 to 2021, and performed a specifically designed mosaic NGS panel for the prospective review of selected patients. DNA was obtained from blood and brain specimens were additionally tested if tissues were available. For further testing, patients had either combined malformations of cortical development (MCDs), neurocutaneous syndromes, or infantile epileptic spasm syndrome (IESS). Patients with IESS had no lesion on MRI. In the selected patients, previous genetic test results were all negative. Overall, 2162 NDD patients underwent conventional target gene NGS panel testing. The diagnostic yield was 31.7% (686/2,162), and 670 (31%) patients had germline variants and 16 (0.7%) had mosaic variants. Among 1476 patients in whom genetic test results were negative, 44 underwent specifically designed mosaic NGS panel testing. With the additional test, three more patients with mosaic variants in the NF1, TSC2, and AKT3 genes were identified from blood. The mean read depth was 50,170 (3615-130,792) and the VAF of detected variants ranged from 1.7% to 10.7%. One patient had a variant in the blood and brain. The diagnostic yield was high in patients with neurocutaneous syndrome (2/7, 28.6%), and low in patients with IESS who had no lesion on MRI (0/17, 0%). The diagnostic yield was 5% (1/20) in patients with MCDs. Mosaic variants were identified in blood and brain in 0.9% (19/2162) of patients with NDDs using a conventional and specifically designed mosaicism NGS panel. These findings will enhance our understanding of NDD and improve patient care and management. 신경발달장애는 인지와 사회성에 영향을 주는 발달 과정에서 발생하는 질환이다. 신경발달장애가 모자이크 유전자 변이에 의해 발생한다는 연구결과가 자주 보고되고 있다. 하지만, 대립 유전자 빈도가 5% 미만으로 낮은 모자이크 변이를 발견하는 것은 쉽지 않다. 본 연구에서는 특수하게 제작된 유전자 패널 검사를 사용하여 말초혈액에서 대립유전자빈도가 낮은 모자이크 변이를 혈액에서 찾고자 하였다. 기존의 유전자 검사를 사용하여 2,162명의 환자 중 686명(31.7%)의 환자에서 유전자 변이 이상을 발견하였다. 이들 중 16명(0.7%)의 환자에서 모자이크 변이가 확인되었다. 유전자 변이가 밝혀지지 않은 44명의 환자에서 특수 제작된 유전자 패널검사를 시행하여 모자이크 변이를 가진 3명(0.2%)의 환자를 추가로 진단할 수 있었다. 이들은 NF1, TSC2, AKT3 유전자에 모자이크 변이를 가지고 있었다. 본 연구에서 신경발달장애 환자 중 총 1%에 달하는 환자가 모자이크변이를 가지고 있음을 확인하였다. 이 결과는 신경발달장애에서 모자이크 변이가 현재까지 보고된 것보다 실제로 더 많이 존재할 수 있음을 시사한다. 앞으로 발달된 검사 방법을 통해 더 많은 신경발달장애 환자에서 모자이크 변이를 확인할 수 있을 것으로 예측된다.