Supplementary Material for: Blended Phenotypes in Siblings: Dual Diagnoses of Nicolaides-Baraitser and Craniosynostosis Syndromes

Introduction: Neurodevelopmental and multiple malformation disorders spanning large phenotypic series can often lead to obscure diagnoses in the clinic. Blended phenotypes from multiple etiologies can compound this issue. We present a rare familial case of two siblings with Nicolaides-Baraitser Syndrome (NCBRS) complicated by an initial diagnosis of syndromic craniosynostosis in one of the patients.
Case Presentation: Whole Exome Sequencing (WES) was performed for the affected siblings using the Agilent SureSelect kit and Illumina HiSeq 2500 system, followed by GATK variant calling and in-house annotation. Sanger sequencing was used to validate candidate variants in all immediate family members. A pathogenic de novo variant in TCF12 (p.Gln646Ter), consistent with craniosynostosis type 3 (CRS3) was identified in the proband, along with a novel likely pathogenic variant in SMARCA2 (p.Ile833Phe) involved in NCBRS. The latter was also detected in the sister and is thus suspected to have arisen through germline mosaicism. Various overlapping phenotypic manifestations complicated clinical diagnosis.
Conclusion: This case expands the molecular and clinical spectrum of NCBRS and CRS3 and underscores the utility of trio-based WES in detecting blended phenotypes of disorders with growing phenotypic spectrums. Paternal germline mosaicism may underlie high recurrence and inform reproductive counseling.

引言：涵盖大范围表型系列的神经发育性与多发畸形疾病，在临床中往往难以明确诊断。多病因引发的混合表型会进一步加剧这一诊断困境。本文报告一例罕见家系病例：两名患有尼古拉德斯-巴赖特斯综合征（Nicolaides-Baraitser Syndrome，NCBRS）的兄弟姐妹，其中一例患者最初被诊断为综合征性颅缝早闭，使病情更为复杂。

病例报告：研究采用安捷伦SureSelect捕获试剂盒与Illumina HiSeq 2500测序平台，对受累兄弟姐妹进行全外显子组测序（Whole Exome Sequencing，WES），随后通过GATK变异检测流程与内部注释体系进行数据分析；同时采用桑格测序（Sanger sequencing）对所有直系家庭成员的候选变异进行验证。结果在先证者中检出与颅缝早闭3型（craniosynostosis type 3，CRS3）相符的TCF12基因致病性新发变异（p.Gln646Ter），同时检出一例与NCBRS相关的新型疑似致病性SMARCA2基因变异（p.Ile833Phe）。该变异同样在患者的姐妹体内检出，因此推测其通过生殖系嵌合（germline mosaicism）产生。多种重叠的表型表现使临床诊断过程更为复杂。

结论：本病例拓展了NCBRS与CRS3的分子及临床表型谱，强调了基于家系三人组的全外显子组测序在检测表型谱不断扩展的疾病混合表型中的应用价值。父系生殖系嵌合可能是该病例高复发风险的潜在原因，可为生殖咨询提供参考依据。