Long QT and Silver Russell syndrome: First case report in a 9-year-old girl Ferran Roses-Noguer, PhD, MD, FHRS,*†1 Maria Martinez-Villar, MD,‡1 Frank Honti, MSc,x Matthew Edwards, MSc,x Jan Till, MD, FHRS,† Deborah J. Morris-Rosendahl, PhDxk From the *Pediatric Cardiology Department, Campus Universitary Vall d’Hebrón, Universiat Autonoma de Barcelona, Barcelona, Spain, †Paediatric Cardiology Department, Royal Brompton and Harefield NHS Foundation Trust, London, United Kingdom, ‡Department of Paediatrics, Vega Baja Hospital, San Bartolomé, Spain, xClinical Genetics and Genomics, Royal Brompton and Harefield NHS Foundation Trust, London, United Kingdom, and kGenomic Medicine, National Heart and Lung Institute, Imperial College London, London, United Kingdom. Introduction hemihypotrophy, and clinodactyly. On the other hand, Long QT syndrome (LQTS) is a genetic-based cause of sud- BWS is an overgrowth syndrome, the clinical and molec- den cardiac death. A prolonged QTc interval on electrocar- ular mirror of SRS.8 diogram (ECG) produces a potentially dangerous substrate Although both LQT1 and SRS loci are in chromosome for ventricular tachycardia and syncope or sudden death.1,2 11p, this is the first time a child manifesting features of The genetics of LQTS have been well documented over both syndromes has been described. We describe a patient the past decade, with the identification of more than 15 genes with LQT, an SRS phenotype, and a de novo 11p15 duplica- corresponding to different disease subtypes.3 LQT1, the most tion and the investigation into the molecular cause of this common form, is caused by loss-of-function of KCNQ1 gene, combination of phenotypes. which encodes a protein that forms a critical part of a voltage- gated potassium channel.4 In LQT1 syndrome, syncope or sudden death is often triggered by emotional or physical Case report stress such as diving and swimming.2 A 9-year-old girl was referred to the pediatric cardiology The locus of KCNQ1 falls within a region of chromo- clinic with a murmur. She was a 27-week gestational age pre- some 11p that contains a cluster of genes subjected to term newborn and her birthweight was 1030 g, which corre- imprinting. Genomic imprinting is the monoallelic sponded to a 50th percentile using the Fenton WHO preterm expression of genes, dependent on the parental origin growth chart (Supplemental Figure S1A). During the first of the chromosome, which is known to play a vital role years of her life, she was diagnosed with postnatal growth in growth and development. Imprinting disorders origi- and length restriction falling below 2 standard deviation nate from a disturbance in this monoallelic expression (SD) using WHO growth charts (Supplemental Figure S1B by disruption or epimutation of imprinted genes.5,6 Aber- and C) and mild hypercalciuria. Her parents and brother are rant genomic imprinting of the 11p15 region has a pivotal healthy and have no apparent phenotype. Moreover, there role in both Silver Russell syndrome (SRS) and the were no cases of sudden cardiac death in a 3-generation fam- Beckwith-Wiedemann syndrome (BWS).7 The molecular ily history. bases of both syndromes are complex and involve the An SRS diagnosis was established as she met 4 of 6 NH- altered expression of multiple growth regulatory genes CSS criteria.9 She had postnatal growth restriction with low in the 11p15.5 genomic region. The SRS is characterized height, relative macrocephaly at birth, prominent forehead by growth failure, typical craniofacial features such and a triangular face, and feeding difficulties, with a body as a prominent forehead and/or triangular face, mass index below 2 SD at 24 months. We did not observe hemihypotrophy or clinodactyly. Her cardiovascular exami- nation revealed an innocent murmur, and she had a structur- KEYWORDS Long QT syndrome; Paediatrics; Silver Russell syndrome; Syncope ally normal heart on echocardiography. However, a 491 ms (Heart Rhythm Case Reports 2020;6:591–595) QTc interval was observed in the ECG performed during 1 Drs Roses-Noguer and Martinez-Villar contributed equally as first authors. the visit (Figure 1). No electrolyte disturbances were identi- Address reprint requests and correspondence: Dr Ferran Roses-Noguer, Pediatric Cardiology Department, Campus Universitary Vall d’Hebrón, Uni- fied on initial blood sample analysis. This abnormal QTc versiat Aut onoma de Barcelona, Passeig de la Vall d’Hebron, 119-129, was observed in several subsequent ECGs. Moreover, a 08035, Barcelona, Spain. E-mail address: froses@vhebron.net. standing test demonstrated a QTc interval of 508 ms at the 2214-0271/© 2020 Heart Rhythm Society. Published by Elsevier Inc. This is an open access article https://doi.org/10.1016/j.hrcr.2020.06.003 under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 592 Heart Rhythm Case Reports, Vol 6, No 9, September 2020 spanned 87 genes, including imprinting control region 1 KEY TEACHING POINTS (ICR1), the IGF2 and H19 genes, and the long noncoding,  Silver Russell syndrome (SRS) is characterized by reverse-transcribed RNA, KCNQ1OT1. A schematic over- growth failure, typical craniofacial features such as view of the 11p15 region, showing the position of the a prominent forehead and/or triangular face, duplication, is shown in Figure 2A. The duplication was sub- hemihypotrophy, and clinodactyly. sequently confirmed and refined to single-exon resolution by copy number variant analysis on a different targeted next-  We describe the first case where a combination of generation sequencing gene panel (Trusight Cardio Panel; Il- an imprinting defect and disruption of the KCNQ1 lumina, San Diego, CA), containing the KCNQ1 and HRAS gene can cause the dual phenotype of SRS and long genes. This analysis showed that the duplication breakpoint QT syndrome (LQTS). disrupts the KCNQ1 gene, with exons 1–12 included in the duplication (Figure 2B). The inheritance of single nucleotide  Ventricular arrhythmia risk appears to be similar to polymorphisms within the duplicated 11p15 region was type 1 LQTS and responds well to beta-blocker analyzed to check the parental origin of the patient’s duplica- therapy. tion allele. Single nucleotide polymorphism rs12628 was informative, showing a skewed allelic balance for the maternal A allele in the patient (G-to-A ratio of 0.35). point of maximal QT-interval stretching and it remained pro- We performed methylation-sensitive multiplex ligation- longed on return to baseline heart rate. dependent probe amplification (Salsa ME030-C3 and Based on these abnormal findings, the patient was started Coffalyser.net; MRC Holland, Amsterdam, Netherlands)10 on atenolol treatment at 1 mg/kg/day. on DNA from the patient and her parents as well as 6 healthy Initial genetic testing using next-generation sequencing control samples, in order to test the methylation status at and the analysis of single nucleotide variants in 13 genes ICR1 and ICR2 (Figure 3). The duplication was again clearly associated with LQTS (AKAP9, ANK2, CACNA1C, CAV3, visible (Figure 3A) and methylation analysis showed hypo- KCNE1, KCNE2, KCNH2, KCNJ2, KCNJ5, KCNQ1, methylation at ICR1 and hypermethylation at ICR2 in the pa- SNC4B, SNC5A, SNTA1) found no pathogenic variants. tient (Figure 3B). This is visible as the decreased percentage Following that result, array comparative genome hybridiza- of methylation, from 50% in normal blood and in the pa- tion was performed and a 2.6 Mb duplication was found in tient’s parents (Figure 3C and D) to an average of 37.75% 11p15 gene (11:223,538 – 2,849,629, hg37). The duplication in the patient (Figure 3B). Hypermethylation was apparent Figure 1 Baseline 12-lead electrocardiograms (ECG) and standing test demonstrating the point of maximal QT-interval stretching. A: The 12-lead ECG at baseline showed the R-R interval measured in lead II is 713 ms, the QT interval is 415 ms, and the corrected QT interval (QTc) is 491 ms. B1: Baseline standing test measured in V5 showed that the R-R interval is 562 ms, the QT interval is 366 ms, and the QTc is 488 ms with a negative T wave. B2: The patient then stands up and at the point of maximal QT-interval stretching the R-R interval is 534 ms, the QT interval is 372 ms, and the QTc is 508 ms and the T wave has a different upright morphology. Roses-Noguer et al Long QT and Silver Russell Syndrome: Case Report 593 Figure 2 Schematic overview of the 11p15.5 region (A) and the result of copy number variant analysis after targeted next-generation sequencing (NGS) in the patient (B). The chromosome 11p15 duplication affecting the HRAS and KCNQ1 genes, these being the only 11p15 genes on the targeted NGS panel, together with the duplication breakpoint in intron 12 are shown. at ICR2, with an average of 72% methylation across the 4 11p15 region is organized in 2 domains, each of them under probes in the patient (Figure 3B), as opposed to the normal the control of its own ICR: ICR1 for the IGF2/H19 domain 50% methylation shown in her parents (Figure 3C and D). and ICR2 for the KCNQ1OT1/CDKN1C domain.11 The telo- Hypomethylation in the patient at ICR1 was further illus- meric ICR1 confers a differential chromatin structure to the trated when the mean of the methylation ratios across 4 2 parental alleles. leading to a reciprocal expression of H19 ICR1 probes in the control samples (SD 0.03) was and IGF2.12 The centromeric ICR2 is maternally methylated compared with the values in the patient (Figure 3E). Despite and controls the monoallelic silencing of the noncoding anti- the relatively low statistical power owing to the small sample sense transcript KCNQ1OT1, as well as the monoallelic number, if one assumes a normal distribution of the control expression of CDKN1C and KCNQ1 in an as-yet-unknown values, the difference between the control and patient values manner.12 This region, when subject to various types of mu- is highly significant (SD .5, P 510e-6). tation, including both genetic and epigenetic abnormalities, A loss-of-function of the KCNQ1 gene, caused by the and depending on the parental inheritance, can be responsible duplication breakpoint interrupting the gene, is consistent for either BWS or SRS.5 The most common cause of SRS with the patient’s phenotype on ECG. After that result, the (approximately 40% of cases) is hypomethylation of the patient was switched to nadolol owing to atenolol intoler- ICR1. However, the exact mechanisms leading to ICR1 hy- ance. No cardiac events have been reported during her pomethylation remain unknown. Uniparental disomy for follow-up. She was subsequently admitted to the emergency chromosome 7 is the next most common cause of SRS department presenting with syncope due to hypoglycemia. (10% of patients). Duplications and other rearrangements However, an implantable loop recorder was implanted to are responsible for only 1%–2% of cases.13 Our findings sug- assist further monitoring as there were potentially multiple gest that the de novo duplication on 11p15 on the maternal reasons for syncope/collapse. After 25 months follow-up allele in our patient alters the methylation at both ICR1 and the patient has had no other cardiac events and the implant- ICR2, thus causing the observed SRS phenotype. able loop recorder remote monitoring has shown no cardiac At least 15 patients with duplications on 11p15 as the arrhythmias. cause of an SRS-like syndrome have been described, with du- plications ranging from 1.6 to 10 Mb 12. Although at least two of these duplications appear to interrupt the KCNQ1 Discussion gene.11,14 LQTS has not been reported in these patients. The 11p15 duplication spans one of the best-known, but most The KCNQ1 imprinted domain exhibits complex tissue- complex, imprinted regions in the genome. The imprinted specific expression patterns at different stages of 594 Heart Rhythm Case Reports, Vol 6, No 9, September 2020 Figure 3 Methylation-sensitive multiplex ligation-dependent probe amplification (MLPA) analysis on chromosome 11p15 in the patient and her parents. A: Copy number MLPA showing the duplication on 11p15 in the patient (purple dots), spanning the H19, IGFR2, KCNQ1, KCNQ1OT1, and CDKN1C genes. B–D: Methylation MLPA in the patient (B) and her parents (C, D), showing the altered methylation status at imprinting control region (ICR) 1 and ICR2 in the patient, with hypomethylation at ICR1 and hypermethylation at ICR2 (purple arrows), and normal methylation patterns in her mother (C) and father (D). E: Mean methyl- ation ratios in 6 healthy controls and the patient’s parents (SD 0.03 for the 8 samples) plotted with the methylation ratios in the patient for ICR1. The reduced methylation at ICR1 in the patient was significantly different from that in the controls (.5 SD for all values, P , 10e-6). Lanes: 1: NSD1-21, 2: NSD1-23, 3: H19- 5, 4: H19-1, 5-6: H19-1 (HhaI), 7-8: H19-up (HhaI), 9-11: H19-up, 12: IGH2-7, 13: IGH2-4 (HhaI), 14: KCNQ1-2, 15: KCNQ1-3, 16: KCNQ1-7, 17: KCNQ1-8, 18: KCNQ1-9, 19-22: KCNQ1OT1-1-ICR (HhaI), 23: KCNQ1-13, 24: KCNQ1-15, 25: KCNQ1-17, 26: CDKN1C-3, 27: CDKN1C-1, 28: CDKN1C-1 (HhaI), 29: ESCO2-1 (HhaI), 30–42: Reference C/M*. development. The antisense noncoding RNA, KCNQ1OT1, occurrence of LQT accompanying SRS, but it is assumed is transcribed from the paternal allele, emerging from intron that most of the SRS-causative defects do not disrupt the 11 of KCNQ1 in an antisense direction. Experiments in mice KCNQ1 gene. The only cardiac defects reported in SRS have demonstrated that transcription of the paternally ex- were bicuspid aortic valve, subaortic stenosis, and ventricular pressed KCNQ1OT1 silences some neighboring genes in septal defect. Until recently, there was a single report of a pa- the embryo, while others are unaffected.15 KCNQ1 is im- tient with mild BWS, an inherited maternal deletion in printed and maternally expressed during early embryogenesis KCNQ1, affecting ICR2, and severe long QT.16 The mother and transitions to biallelic expression in a tissue-specific of the patient described in that paper (56-year-old woman) manner. In the embryonic mouse heart, the transition to bial- had no history of syncope attacks or palpitation and her Hol- lelic expression occurs at approximately E14.5 and appears ter monitoring did not reveal any significant arrhythmia. She to be quite consistent.15 The epigenetic profile of KCNQ1 had a deletion on her paternal chromosome 11, SRS-like expression during human cardiac development, however, symptoms, and mild QT prolongation (QTc 463 ms) with has not yet been fully elucidated, and may well play a role flat T waves in V2–V3. More recently, an additional 3 patients in the extensive phenotypic variability shown in the expres- were reported with both BWS and LQTS, with predicted sion of LQTS.15 KCNQ1 haploinsufficiency and loss of methylation of In our patient, the duplication breakpoint is located in IC2.6 We therefore propose that the combination of an intron 12 of KCNQ1, and therefore disrupts KCNQ1, pre- imprinting defect and disruption of the KCNQ1 gene on the dicted to cause loss-of-function and the QTc prolongation. maternal allele in our patient has caused the dual phenotype Interestingly, there are no reports in the literature of the of SRS and LQTS. We believe this is the first time the 2 Roses-Noguer et al Long QT and Silver Russell Syndrome: Case Report 595 syndromes have been described together but think this ~ 8. Ounap K. 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