Urakawa Tatsuki, Kanamaru Yuri, Amano Naoko, Uchida Akira, Fukami Maki, Kagami Masayo
Department of Molecular Endocrinology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-Ku, Tokyo , 157-8535, Japan.
Department of Pediatrics, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 852-8102, Japan.
Clin Epigenetics. 2025 Jun 9;17(1):97. doi: 10.1186/s13148-025-01907-y.
Beckwith-Wiedemann syndrome (BWS) is a congenital imprinting disorder (ID) caused by molecular defects in the 11p15.5 imprinted region, such as hypomethylation of the KCNQ1OT1:TSS-differentially methylated region (KCNQ1OT1-DMR) and hypermethylation of the H19/IGF2:IG-DMR, and maternal CDKN1C pathogenic variants, with various clinical characteristics, including overgrowth and macroglossia. Recently, the concept of Beckwith-Wiedemann spectrum (BWSp) and a clinical scoring system for BWS have been proposed, and cases with four or more points are diagnosed with classic BWS, and 20% of cases with BWS have no molecular defects in the 11p15.5 imprinted region. Pseudohypoparathyroidism type 1B (PHP1B, alias inactivating parathyroid hormone (PTH)/PTH-related protein signaling disorder 3) has characteristics of hormone resistance, particularly PTH, caused by methylation defects in DMRs at the GNAS locus (GNAS-DMRs). Some cases with PHP1B show postnatal overgrowth, which overlaps the BWS-phenotype. However, no studies have conducted a multi-locus methylation analysis for the ID-responsible DMRs other than the DMRs in 11p15.5 in cases with the BWS-phenotype and without molecular defects in the 11p15.5 imprinted region.
We conducted methylation analysis using pyrosequencing in 77 patients showing the BWS-phenotype without molecular defects in the 11p15.5 imprinted region. Consequently, we identified three patients with methylation defects in the GNAS-DMRs. Patients 1, 2, and 3 had 9, 5, and 4 points in a BWSp score, respectively. All three patients had macroglossia and postnatal overgrowth. Further analyses, methylation-specific multiple ligation-dependent probe amplification for multiple DMRs, array-based methylation analysis, exome sequencing, array comparative genome hybridization analysis, and microsatellite marker analysis showed 9p deletion in Patient 1 and paternal uniparental isodisomy of chromosome 20 in Patient 2 together with multiple methylation defects in DMRs other than the GNAS-DMRs. Patient 3 had methylation defects in only the GNAS-DMRs.
Methylation defects in the GNAS-DMRs can cause the BWS-phenotype. For cases with the BWS-phenotype but no molecular defects in the 11p15.5 imprinted region, methylation analysis for the DMRs at the GNAS locus should be considered.
贝克威思-维德曼综合征（BWS）是一种先天性印记障碍（ID），由11p15.5印记区域的分子缺陷引起，如KCNQ1OT1：转录起始位点差异甲基化区域（KCNQ1OT1-DMR）的低甲基化、H19/IGF2：印记基因差异甲基化区域（IG-DMR）的高甲基化以及母源CDKN1C致病性变异，具有多种临床特征，包括生长过度和巨舌症。最近，提出了贝克威思-维德曼谱系（BWSp）的概念和BWS的临床评分系统，得分4分及以上的病例被诊断为经典BWS，20%的BWS病例在11p15.5印记区域没有分子缺陷。1B型假性甲状旁腺功能减退症（PHP1B，别名甲状旁腺激素（PTH）/PTH相关蛋白信号失活障碍3）具有激素抵抗的特征，尤其是对PTH的抵抗，由GNAS基因座的差异甲基化区域（GNAS-DMRs）的甲基化缺陷引起。一些PHP1B病例表现出出生后生长过度，这与BWS表型重叠。然而，对于具有BWS表型且在11p15.5印记区域没有分子缺陷的病例，尚未有研究对除11p15.5中的DMRs之外的ID相关DMRs进行多位点甲基化分析。
我们对77例表现出BWS表型且在11p15.5印记区域没有分子缺陷的患者进行了焦磷酸测序甲基化分析。结果，我们鉴定出3例GNAS-DMRs存在甲基化缺陷的患者。患者1、2和3的BWSp评分分别为9分、5分和4分。所有3例患者均有巨舌症和出生后生长过度。进一步分析，对多个DMRs进行甲基化特异性多重连接依赖探针扩增、基于芯片的甲基化分析、外显子测序、阵列比较基因组杂交分析和微卫星标记分析显示，患者1存在9号染色体缺失，患者2存在20号染色体父源单亲二体，同时在除GNAS-DMRs之外的DMRs中存在多个甲基化缺陷。患者3仅在GNAS-DMRs存在甲基化缺陷。
GNAS-DMRs的甲基化缺陷可导致BWS表型。对于具有BWS表型但在11p15.5印记区域没有分子缺陷的病例，应考虑对GNAS基因座的DMRs进行甲基化分析。
