Comprehensive Analysis of Clinical Spectrum and Genotype Associations in Chinese and Literature Reported KBG Syndrome
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842 Original Article Comprehensive analysis of clinical spectrum and genotype associations in Chinese and literature reported KBG syndrome Qiuyue Li, Chengjun Sun, Lin Yang, Wei Lu, Feihong Luo^ Department of Pediatric Endocrinology and Inherited Metabolic Diseases, Children’s Hospital of Fudan University, Shanghai, China Contributions: (I) Conception and design: Q Li, C Sun, F Luo; (II) Administrative support: L Yang, F Luo; (III) Provision of study materials or patients: L Yang, W Lu; (IV) Collection and assembly of data: Q Li, C Sun, L Yang; (V) Data analysis and interpretation: Q Li, C Sun, W Lu; (VI) Manuscript writing: All authors; (VII) Final approval of manuscript: All authors. Correspondence to: Feihong Luo. Department of Endocrinology and Inherited Metabolic Diseases, Children’s Hospital of Fudan University, 399 Wanyuan Road, Shanghai, China. Email: [email protected]. Background: Patients with KBG Syndrome due to ANKRD11 mutations and 16q24.3 microdeletions including ANKRD11 were identified. Classical and most frequent phenotypes include various degrees of intelligence disability (ID), short stature (SS), delayed bone age, macrodontia, distinctive facial features and skeletal anomalies. The variable expressivity of KBG syndrome makes it challenging to establish genotype- phenotype correlations, which also affects further studies for this novel syndrome. We aim to report three unrelated patients with KBG syndrome caused by ANKRD11 gene pathological variants and to evaluate potential associations among ANKRD11 gene variant types, the 16q24.3 microdeletion, and the clinical spectrum of KBG syndrome. Methods: The genetic etiology of three unreported KBG patients was identified by whole exome sequencing and confirmed via Sanger sequencing. Literature review was conducted to summarize the phenotype-genotype relationship based on three unreported Chinese cases and 186 reported cases. Results: Two pathological variants (c.7407dupC, p.P2530Rfs*61; c.G3046A, p.D1016N) and one reported variant (c.6792dupC, p. P2271Pfs*8) were detected in our patients. Compared with the 16q24.3 microdeletion, patients harboring ANKRD11 gene mutations showed significantly higher frequency of malformations including macrodontia, long philtrum, abnormal eyebrows, widely spaced eyes, anteverted nares, eyelid ptosis, brachydactyly, brachycephaly (P<0.05), and significantly lower risk of congenital heart diseases and frontal bossing (P<0.05). The intellectual disability (ID) was significantly milder among patients carrying truncating variants located between repression domain 1 (RD1) and activation domain (AD) than those carrying mutations disrupting repression domain 2 (RD2) alone and disrupting all functional domain (RD1, AD or RD2) (P<0.05). Conclusions: Novel pathological variants harbored in the ANKRD11 gene contribute to the KBG syndrome variant spectrum. ANKRD11 gene variants disrupting RD1 and RD2 or RD2 alone are more likely to have more severe ID, which warrants different intervention strategies for KBG syndrome. Keywords: KBG syndrome; ANKRD11 gene; 16q24.3 microdeletion; short stature (SS); intellectual disability; genotype-phenotype association Submitted Nov 12, 2020. Accepted for publication Mar 05, 2020. doi: 10.21037/tp-20-385 View this article at: http://dx.doi.org/10.21037/tp-20-385 ^ ORCID: 0000-0002-6433-7994. © Translational Pediatrics. All rights reserved. Transl Pediatr 2021;10(4):834-842 | http://dx.doi.org/10.21037/tp-20-385 Translational Pediatrics, Vol 10, No 4 April 2021 835 Introduction Patients and diagnose criteria The KBG syndrome (MIM #148050), named after the Three unrelated probands were clinical diagnosed as having first reported families (1), is an autosomal dominant disease KBG symptoms using the diagnostic criteria proposed currently known to be caused by either an ANKRD11 gene by Skjei et al. (6). All three patients presented four of the mutation (2) or a microdeletion in chromosome 16q24.3 following major clinical features: macrodontia, ID, SS, including the ANKRD11 gene (3-5). The KBG syndrome is delayed bone age, hand findings, costovertebral anomalies, characterized by macrodontia, intellectual disability (ID), short characteristic facial dysmorphism, and the presence of a first- stature (SS), delayed bone age, hand findings, costovertebral degree relative with the syndrome. The family members were anomalies, characteristic facial dysmorphism, and the presence invited for further clinical investigations and genetic tests of a first-degree relative with the syndrome (6). after acquiring informed consent from all parents. The ANKRD11 gene encodes an ankyrin repeat- containing protein (ANKRD11 or previous ANCO-1), Whole exome sequencing (WES) analysis which is indispensable in neuron proliferation (7). Earlier in vitro study showed that ANKRD11 protein acts as a WES was performed in each family by WuXi transcriptional repressor (8) and functions through its two NextCODE Genomics, Shanghai, China (CLIA Lab transcriptional repression domains (RDs: RD1, aa 318–611; ID: 99D2064856) (20). Briefly, exome capture was and RD2, aa 2,369–2,663) and one activation domain (AD, performed using the Agilent SureSelect Human All Exon aa 1,851–2,145) (9). In addition, the RD2 domain regulates V5, Illumina TruSeq Rapid PE Cluster, and SBS kits the activity of the ANKRD11 protein and maintains the (Agilent Technologies, Santa Clara, CA, USA). Illumina protein’s appropriate degradation (10). HiSeq provided the 2000/2500 platform for WES. In vivo studies showed that either ANKRD11 gene Reads alignment were referenced to the human genome knockdown or the accumulation of truncated ANKRD11 sequence (http://genome.ucsc.edu) through the Burrows- protein can result in the KBG phenotype (10,11). Recent Wheeler Aligner v.0.6.2. Duplicate paired-end reads advances in genetic analysis have allowed the identification were marked with Picard v.1.55 (https://broadinstitute. of patients with extremely mild symptoms of the KBG github.io/picard/). The base quality score recalibration, syndrome (12-16). Patients with the KBG syndrome, who indel realignment, and variant discovery were performed commonly seek medical consultation and treatment owing by the Genome Analysis Toolkit v.2.3-9. Variants were to malformations, ID, or SS, demonstrate great variations annotated using a pipeline developed in-house (20) and in these traits, and proper clinical diagnosis is frequently filtered in the gnomAD, Exome Variant Server, dbSNP difficult (17-19). databases, and Exome Aggregation Consortium. Studies focusing on the relationship between genotype and phenotype in the KBG syndrome remain scarce. Here Systematic literature review we report three new genetically diagnosed Chinese KBG patients and further analyze the underlying genotype- Articles in the databases Ovid MEDLINE and Web of phenotype relationship in combination with 186 cases Knowledge (2011 June to 2019 Aug) were searched using reported in the literature. the following terms: ankyrin repeat domain 11, ANKRD11, We present the following article in accordance with ankyrin repeats containing cofactor, ANCO-1, 16q24.3, and the MDAR reporting checklist (available at http://dx.doi. KBG. OMIM and ClinVar databases were also searched for org/10.21037/tp-20-385). mutations in the ANKRD11 gene and related publications in Human Gene Mutation Database (HGMD). In addition, a manual search for references of initially identified articles Methods was carried out. The clinical data [gender, family of origin, The study was conducted in accordance with the age at diagnosis, and types of ANKRD11 gene mutation Declaration of Helsinki (as revised in 2013). The study was (in reference to ENST00000378330.7)] or 16q23.4 approved by the ethics committee of the Children’s Hospital microdeletion (aligned to GRCh38 coordinates using the of Fudan University (No. 2017237), and written informed UCSC liftover tool) of reported cases in each publication consent was obtained from the patient. were collected. Literature selection and data extraction were © Translational Pediatrics. All rights reserved. Transl Pediatr 2021;10(4):834-842 | http://dx.doi.org/10.21037/tp-20-385 836 Li et al. Genotype-phenotype association of KBG syndrome performed independently by two investigators (Q Li and C age of 8 years, she had a height of 110 cm (−3.4 SD) and Sun). The data were then reviewed by a third investigator (F weight of 17.7 kg (−2.5 SD). She had triangular face, low Luo) and the conflicts were resolved by consensus. posterior hairline, arched eyebrows, long eye lashes, broad nasal low bridge, flat philtrum, thin upper lip, wide upper central incisors and prominent anteverted ears, short fingers Intelligence quotient (IQ) and body height classification with fifth finger clinodactyly (Figure S1A,B). A skeletal The degree of ID was determined based on the description survey revealed 1-year delayed bone age and intoeing of intelligence estimation in each report (by the measurement (pigeon toes). Her IQ was 56. The patient was found to of either IQ or equivalent such as developmental quotient carry de novo mutation (c.6792dupC, p. P2271Pfs*8) in derived from milestones, school attendance, levels of special ANKRD11 gene (Figure S1C). Examination of both parents educational need, or basis of daily skills) and categorized revealed normal phenotypes. Her father (height 174 cm, according to Diagnostic and Statistical Manual of Mental +0.32 SD) was an engineer, and her mother (height 162 cm, Disorders, 4th edition (DSM-IV) stages of ID (i.e.,