Contribution of gene mutations to Silver-Russell syndrome phenotype: multigene sequencing analysis in 92 etiology-unknown patients

Background Silver-Russell syndrome (SRS) is characterized by growth failure and dysmorphic features. Major (epi)genetic causes of SRS are loss of methylation on chromosome 11p15 (11p15 LOM) and maternal uniparental disomy of chromosome 7 (upd(7)mat). However,IGF2,CDKN1C,HMGA2, andPLAG1mutations infrequently cause SRS. In addition, other imprinting disturbances, pathogenic copy number variations (PCNVs), and monogenic disorders sometimes lead to SRS phenotype. This study aimed to clarify the frequency and clinical features of the patients with gene mutations among etiology-unknown patients with SRS phenotype. Results Multigene sequencing was performed in 92 out of 336 patients referred to us for genetic testing for SRS. The clinical features of the patients were evaluated based on the Netchine-Harbison clinical scoring system. None of the patients showed 11p15 LOM, upd(7)mat, abnormal methylation levels for six differentially methylated regions (DMRs), namely,PLAGL1:alt-TSS-DMR on chromosome 6,KCNQ1OT1:TSS-DMR on chromosome 11,MEG3/DLK1:IG-DMR on chromosome 14,MEG3:TSS-DMR on chromosome 14,SNURF:TSS-DMR on chromosome 15, andGNAS A/B:TSS-DMR on chromosome 20, PCNVs, or maternal uniparental disomy of chromosome 16. Using next-generation sequencing and Sanger sequencing, we screened four SRS-causative genes and 406 genes related to growth failure and/or skeletal dysplasia. We identified four pathogenic or likely pathogenic variants in responsible genes for SRS (4.3%:IGF2in two patients,CDKN1C, andPLAG1), and five pathogenic variants in causative genes for known genetic syndromes presenting with growth failure (5.4%:IGF1Rabnormality (IGF1R), SHORT syndrome (PIK3R1), Floating-Harbor syndrome (SRCAP), Pitt-Hopkins syndrome (TCF4), and Noonan syndrome (PTPN11)). Functional analysis indicated the pathogenicity of theCDKN1Cvariant. The variants we detected inCDKN1CandPLAG1were the second and third variants leading to SRS, respectively. Our patients withCDKN1CandPLAG1variants showed similar phenotypes to previously reported patients. Furthermore, our data confirmedIGF1Rabnormality, SHORT syndrome, and Floating-Harbor syndrome are differential diagnoses of SRS because of the shared phenotypes among these syndromes and SRS. On the other hand, the patients with pathogenic variants in causative genes for Pitt-Hopkins syndrome and Noonan syndrome were atypical of these syndromes and showed partial clinical features of SRS. Conclusions We identified nine patients (9.8%) with pathogenic or likely pathogenic variants out of 92 etiology-unknown patients with SRS phenotype. This study expands the molecular spectrum of SRS phenotype.