Haploinsufficiency for ANKRD11-flanking genes makes the difference between KBG and 16q24.3 microdeletion syndromes: 12 new cases

KBG syndrome: report and follow-up on three unrelated patients observed at different ages

BACKGROUND

KBG syndrome (MIM #148050) is a rare genetic disease, showing an autosomal dominant pattern of inheritance. It was first described by Herrmann et al. in 1975 in three affected families, whose initial letters gave origin to the acronym. A peculiar facies including triangular face, synophrys, macrodontia of the upper central incisors, as well as short stature, skeletal defects and neurodevelopmental disorders (developmental delay, intellectual disability, epilepsy) are the main features of the syndrome. Mutations of the ankirin repeat domain 11 gene (ANKRD11), which harbors at chromosome 16q24.3, have been associated to the syndrome. The encoded protein inhibits ligand-dependent activation of transcription. Due to the growing number of detected ANKRD11 variants associated to phenotypes with various degree of severity, the precise definition of the clinical and genomic profiles of patients is important, also in the perspective of a better understanding of the molecular bases of the disease, genotype-phenotype correlation, and management of affected subjects.

CASES PRESENTATION

We report on three unrelated patients, observed in as many different Italian (Sicily, Veneto and Friuli-Venezia-Giulia regions) Pediatric Neurology and Medical Genetics outpatient services, showing variously present typical dysmorphic features (e.g., triangular face, macrodontia of upper incisors, brachydactyly), growth retardation and impaired neurodevelopmental profiles (i.e. developmental delay, EEG abnormalities/epilepsy) compatible with KBG syndrome diagnosis. In Patient 1, next generation sequencing analysis of a panel of genes involved in developmental delay and autism spectrum disorders detected two mutations, a pathogenic heterozygous frameshift variant of the ANKRD11 gene (already described in the literature), and a heterozygous missense one in EHMT1 (previously reported as well, and associated with Kleefstra syndrome); in Patient 2, array comparative genomic hybridization (a-CGH) analysis identified a 634 Kb 16q24.3-24.3 deletion involving several genes (CDT1, APRT, GALNS, TRAPPC2L, ACSF3, CDH15), besides ANKRD11, some of which are related with developmental disorders. Finally in Patient 3, Sanger sequencing of the ANKRD11 gene, performed due to the specific diagnostic suspicion raised for precocious teething observed at age 3 months, evidenced an intragenic deletion allowing thus an early diagnosis of disease.

CONCLUSIONS

We underline similarities and differences among our patients, and their specific genetic and clinical features, in addition to the variable diagnostic tests used for the diagnosis, reached at different developmental age, i.e. infancy, childhood and adolescence. Pediatricians must be aware of KBG syndrome and should be able, as well, to raise the diagnostic suspicion, especially in the presence of peculiar dysmorphic features, short stature, developmental delay, intellectual disability and epilepsy. Prompt diagnosis may allow to better address any associated emerging neuropsychological and behavioral issues improving the quality of life of the patient and the whole family.

Assessment of Adaptive Functioning and the Impact of Seizures in KBG Syndrome

This study aimed to examine the adaptive functioning status and the impact of epileptic seizures on neurocognitive outcomes in KBG syndrome, a rare genetic neurodevelopmental disorder characterized by pathogenic variants in ANKRD11. A single clinician interviewed individuals and families with genetically confirmed cases of KBG syndrome. Trained professionals also conducted assessments using the Vineland-3 Adaptive Behavior Scales. The assessment covered the domains of communication, daily living skills, socialization, and maladaptive behaviors, and then compared individuals with and without epilepsy. Further comparisons were made with data from interviews and participants' medical records. Thirty-nine individuals (22 males, 17 females) with KBG syndrome, confirmed through genetic analysis, were interviewed via videoconferencing, followed by Vineland-3 assessment by trained raters. Individuals with KBG syndrome came from 36 unique families spanning 11 countries. While the KBG cohort displayed lower overall adaptive behavior composite scores compared with the average population, several members displayed standard scores at or higher than average, as well as higher scores compared with those with the neurodevelopmental disorder Ogden syndrome. Within the KBG cohort, males consistently scored lower than females across all domains, but none of these categories reached statistical significance. While the group with epilepsy exhibited overall lower scores than the nonseizure group in every category, statistical significance was only reached in the written communication subdomain. Our research provides insights that can aid in epilepsy screening and inform assessment strategies for neurocognitive functioning in those with this condition. The cohort performed overall higher than expected, with outliers existing in both directions. Although our results suggest that seizures might influence the trajectory of KBG syndrome, the approaching but overall absence of statistical significance between study groups underscores the need for a more extensive cohort to discern subtle variations in functioning.

16q24.3 Microdeletions Disrupting Upstream Non-Coding Region of ANKRD11 Cause KBG Syndrome

Background: KBG syndrome is a multisystem developmental disorder characterized by macrodontia of the upper permanent incisors, distinctive facial features, a short stature, developmental delay, variable intellectual disability, and behavioral issues. Heterozygous chromosomal deletion encompassing the partial or entire ANKRD11 gene, as well as the loss of function mutations, result in haploinsufficiency of the gene, leading to KBG syndrome. This indicates that precise levels of ANKRD11 transcripts or protein are essential for human development. Clinical report: Here, we report three individuals who present with clinical features of KBG syndrome. These individuals carry microdeletions encompassing only the non-coding exon 1 of ANKRD11 and its upstream region. Our molecular analysis showed that this deletion leads to reduction in the ANKRD11 transcript and global transcriptome alterations similar to those seen in KBG syndrome patients. Conclusions: We concluded that microdeletions involving non-coding exon 1 of ANKRD11 lead to KBG syndrome. Our study suggests the utility of transcriptome analysis in aiding the interpretation of novel copy number variants in the non-coding genomic region of ANKRD11.

The dual role of CCND1 in heterotopic ossification: A Non-canonical Pathway for Celecoxib treatment

Objective

To explore the effective targets of Celecoxib in the treatment of heterotopic ossification using network pharmacology methods.

Methods

Potential molecules related to heterotopic ossification were obtained by retrieving the GEO and CTD databases and intersecting them. Potential binding targets of Celecoxib were acquired from the STITCH database. A protein-protein interaction network was constructed between potential binding targets of Celecoxib and potential related molecules of heterotopic ossification using the STRING database. Molecules in the protein-protein interaction network were further analyzed using GO and KEGG enrichment analysis in R software, followed by enrichment analysis of active molecules in the Celecoxib-heterotopic ossification target dataset. Hub genes were selected based on the "degree" value and enrichment within the protein-protein interaction network. The binding affinity of hub genes to Celecoxib was observed using molecular docking techniques. Finally, in vitro experiments were conducted to validate the effectiveness of hub genes and explore their regulatory role in the progression of heterotopic ossification. Additionally, the therapeutic effect of Celecoxib, which modulates the expression of the hub genes, was investigated in the treatment of heterotopic ossification.

Results

568 potential molecules related to heterotopic ossification and 76 potential binding targets of Celecoxib were identified. After intersection, 13 potential functional molecules in Celecoxib's treatment of heterotopic ossification were obtained. KEGG analysis suggested pathways such as Rheumatoid arthritis, NF-kappa B signaling pathway, Pathways in cancer, Antifolate resistance, MicroRNAs in cancer play a role in the treatment of heterotopic ossification by Celecoxib. Further enrichment analysis of the 13 potential functional molecules identified 5 hub genes: IL6, CCND1, PTGS2, IGFBP3, CDH1. Molecular docking results indicated that Celecoxib displayed excellent binding affinity with CCND1 among the 5 hub genes. Experimental validation found that CCND1 is highly expressed in the progression of heterotopic ossification, promoting heterotopic ossification in the early stages and inhibiting it in the later stages, with Celecoxib's treatment of heterotopic ossification depending on CCND1.

Conclusion

In the process of treating heterotopic ossification with Celecoxib, immune and inflammatory signaling pathways play a significant role. The therapeutic effect of Celecoxib on heterotopic ossification depends on the hub gene CCND1, which plays different roles at different stages of the progression of heterotopic ossification, ultimately inhibiting the occurrence of heterotopic ossification.

Olfactory bulb anomalies in KBG syndrome mouse model and patients

ANKRD11 (ankyrin repeat domain 11) is a chromatin regulator and the only gene associated with KBG syndrome, a rare neurodevelopmental disorder. We have previously shown that Ankrd11 regulates murine embryonic cortical neurogenesis. Here, we show a novel olfactory bulb phenotype in a KBG syndrome mouse model and two diagnosed patients. Conditional knockout of Ankrd11 in murine embryonic neural stem cells leads to aberrant postnatal olfactory bulb development and reduced size due to reduction of the olfactory bulb granule cell layer. We further show that the rostral migratory stream has incomplete migration of neuroblasts, reduced cell proliferation as well as aberrant differentiation of neurons. This leads to reduced neuroblasts and neurons in the olfactory bulb granule cell layer. In vitro, Ankrd11-deficient neural stem cells from the postnatal subventricular zone display reduced migration, proliferation, and neurogenesis. Finally, we describe two clinically and molecularly confirmed KBG syndrome patients with anosmia and olfactory bulb and groove hypo-dysgenesis/agenesis. Our report provides evidence that Ankrd11 is a novel regulator of olfactory bulb development and neuroblast migration. Moreover, our study highlights a novel clinical sign of KBG syndrome linked to ANKRD11 perturbations in mice and humans.

Ocular manifestations in a cohort of 43 patients with KBG syndrome

Ophthalmological conditions are underreported in patients with KBG syndrome, which is classically described as presenting with dental, developmental, intellectual, skeletal, and craniofacial abnormalities. This study analyzed the prevalence of four ophthalmological conditions (strabismus, astigmatism, myopia, hyperopia) in 43 patients with KBG syndrome carrying variants in ANKRD11 or deletions in 16q24.3 and compared it to the literature. Forty-three patients were recruited via self-referral or a private Facebook group hosted by the KBG Foundation, with 40 of them having pathogenic or likely pathogenic variants. Virtual interviews were conducted to collect a comprehensive medical history verified by medical records. From these records, data analysis was performed to calculate the prevalence of ophthalmological conditions. Out of the 40 participants with pathogenic or likely pathogenic variants, strabismus was reported in 9 (22.5%) participants, while astigmatism, myopia, and hyperopia were reported in 11 (27.5%), 6 (15.0%), and 8 (20.0%) participants, respectively. Other reported conditions include anisometropia, amblyopia, and nystagmus. When compared to the literature, the prevalence of strabismus and refractive errors is higher than other studies. However, more research is needed to determine if variants in ANKRD11 play a role in abnormal development of the visual system. In patients with established KBG syndrome, screening for misalignment or refractive errors should be done, as interventions in patients with these conditions can improve functioning and quality of life.

Determining the Linguistic Profile of Children With Rare Genetic Disorders

PURPOSE

Language studies on populations with rare genetic disorders are limited. Hence, there is little data on commonly found or expected developmental linguistic traits and cognitive mechanisms that may be impaired. Based on the hypothesis that there is a close connection between language and cognition and the relevance of specific genetic changes in the development of each, our goal was to provide linguistic data on relationships with other executive functioning mechanisms.

METHOD

This study assessed language skills, communicative behaviors, and executive functions in four children, aged 7-9 years, with rare genetic disorders, using standardized protocols and tests.

RESULTS

The findings revealed different levels of language impairment and executive functioning problems in each case. The overall executive function index performance for each of the four cases studied was clinically significantly high, indicating executive dysfunction.

CONCLUSIONS

The cases analyzed illustrate different types of atypical development that affect both language and other cognitive mechanisms and underscore the importance of executive skills and the various ways in which they are involved in diverse levels of language that might be affected to a greater or lesser degree in rare genetic disorders. In conclusion, we found that language dysfunction is a salient feature of the rare genetic disorders included in our study, although this is not necessarily true for all genetic disorders. Along with these conclusive results, we performed a qualitative analysis of the linguistic and cognitive components that enable functional communication in order to allow optimal interpretation of the data we have collected, laying the foundations for a more effective therapeutic approach.

Epilepsy is an important feature of KBG syndrome associated with poorer developmental outcome

OBJECTIVE

The aim of this study was to describe the epilepsy phenotype in a large international cohort of patients with KBG syndrome and to study a possible genotype-phenotype correlation.

METHODS

We collected data on patients with ANKRD11 variants by contacting University Medical Centers in the Netherlands, an international network of collaborating clinicians, and study groups who previously published about KBG syndrome. All patients with a likely pathogenic or pathogenic ANKRD11 variant were included in our patient cohort and categorized into an "epilepsy group" or "non-epilepsy group". Additionally, we included previously reported patients with (likely) pathogenic ANKRD11 variants and epilepsy from the literature.

RESULTS

We included 75 patients with KBG syndrome of whom 26 had epilepsy. Those with epilepsy more often had moderate to severe intellectual disability (42.3% vs 9.1%, RR 4.6 [95% CI 1.7-13.1]). Seizure onset in patients with KBG syndrome occurred at a median age of 4 years (range 12 months - 20 years), and the majority had generalized onset seizures (57.7%) with tonic-clonic seizures being most common (23.1%). The epilepsy type was mostly classified as generalized (42.9%) or combined generalized and focal (42.9%), not fulfilling the criteria of an electroclinical syndrome diagnosis. Half of the epilepsy patients (50.0%) were seizure free on anti-seizure medication (ASM) for at least 1 year at the time of last assessment, but 26.9% of patients had drug-resistant epilepsy (failure of ≥2 ASM). No genotype-phenotype correlation could be identified for the presence of epilepsy or epilepsy characteristics.

SIGNIFICANCE

Epilepsy in KBG syndrome most often presents as a generalized or combined focal and generalized type. No distinctive epilepsy syndrome could be identified. Patients with KBG syndrome and epilepsy had a significantly poorer neurodevelopmental outcome compared with those without epilepsy. Clinicians should consider KBG syndrome as a causal etiology of epilepsy and be aware of the poorer neurodevelopmental outcome in individuals with epilepsy.

Deep phenotyping of the neuroimaging and skeletal features in KBG syndrome: a study of 53 patients and review of the literature

BACKGROUND

KBG syndrome is caused by haploinsufficiency of ANKRD11 and is characterised by macrodontia of upper central incisors, distinctive facial features, short stature, skeletal anomalies, developmental delay, brain malformations and seizures. The central nervous system (CNS) and skeletal features remain poorly defined.

METHODS

CNS and/or skeletal imaging were collected from molecularly confirmed individuals with KBG syndrome through an international network. We evaluated the original imaging and compared our results with data in the literature.

RESULTS

We identified 53 individuals, 44 with CNS and 40 with skeletal imaging. Common CNS findings included incomplete hippocampal inversion and posterior fossa malformations; these were significantly more common than previously reported (63.4% and 65.9% vs 1.1% and 24.7%, respectively). Additional features included patulous internal auditory canal, never described before in KBG syndrome, and the recurrence of ventriculomegaly, encephalic cysts, empty sella and low-lying conus medullaris. We found no correlation between these structural anomalies and epilepsy or intellectual disability. Prevalent skeletal findings comprised abnormalities of the spine including scoliosis, coccygeal anomalies and cervical ribs. Hand X-rays revealed frequent abnormalities of carpal bone morphology and maturation, including a greater delay in ossification compared with metacarpal/phalanx bones.

CONCLUSION

This cohort enabled us to describe the prevalence of very heterogeneous neuroradiological and skeletal anomalies in KBG syndrome. Knowledge of the spectrum of such anomalies will aid diagnostic accuracy, improve patient care and provide a reference for future research on the effects of ANKRD11 variants in skeletal and brain development.

Audiological phenotyping evaluation in KBG syndrome: Description of a multicenter review

OBJECTIVES

Our objective was to reinforce clinical knowledge of hearing impairment in KBG syndrome. KBG syndrome is a rare genetic disorder due to monoallelic pathogenic variations of ANKRD11.The typical phenotype includes facial dysmorphism, costal and spinal malformation and developmental delay. Hearing loss in KBG patients has been reported for many years, but no study has evaluated audiological phenotyping from a clinical and an anatomical point of view.

METHODS

This French multicenter study included 32 KBG patients with retrospective collection of data on audiological features, ear imaging and genetic investigations.

RESULTS

We identified a typical audiological profil in KBG syndrome: conductive (71%), bilateral (81%), mild to moderate (84%) and stable (69%) hearing loss, with some audiological heterogeneity. Among patients with an abnormality on CT imaging (55%), ossicular chain impairment (67%), fixation of the stapes footplate (33%) and inner-ear malformations (33%) were the most common abnormalities.

CONCLUSION

We recommend a complete audiological and radiological evaluation and an ENT-follow up in all patients presenting with KBG Syndrome. Imaging evaluation is necessary to determine the nature of lesions in the middle and inner ear.

A Gene-Based Algorithm for Identifying Factors That May Affect a Speaker's Voice

Over the past decades, many machine-learning- and artificial-intelligence-based technologies have been created to deduce biometric or bio-relevant parameters of speakers from their voice. These voice profiling technologies have targeted a wide range of parameters, from diseases to environmental factors, based largely on the fact that they are known to influence voice. Recently, some have also explored the prediction of parameters whose influence on voice is not easily observable through data-opportunistic biomarker discovery techniques. However, given the enormous range of factors that can possibly influence voice, more informed methods for selecting those that may be potentially deducible from voice are needed. To this end, this paper proposes a simple path-finding algorithm that attempts to find links between vocal characteristics and perturbing factors using cytogenetic and genomic data. The links represent reasonable selection criteria for use by computational by profiling technologies only, and are not intended to establish any unknown biological facts. The proposed algorithm is validated using a simple example from medical literature-that of the clinically observed effects of specific chromosomal microdeletion syndromes on the vocal characteristics of affected people. In this example, the algorithm attempts to link the genes involved in these syndromes to a single example gene (FOXP2) that is known to play a broad role in voice production. We show that in cases where strong links are exposed, vocal characteristics of the patients are indeed reported to be correspondingly affected. Validation experiments and subsequent analyses confirm that the methodology could be potentially useful in predicting the existence of vocal signatures in naïve cases where their existence has not been otherwise observed.

Deletion of first noncoding exon in ANKRD11 leads to KBG syndrome

Phenotypic features of KBG syndrome include craniofacial anomalies, short stature, cognitive disability and behavioral findings. The syndrome is caused by heterozygous pathogenic single nucleotide variants and indels in ANKRD11, or a heterozygous deletion of 16q24.3 that includes ANKRD11. We performed genome sequencing on a patient with clinical manifestations of KBG syndrome including distinct craniofacial features as well as a history of mild intellectual disability and attention-deficit hyperactivity disorder. This led to the identification of a 43 kb intragenic deletion of ANKRD11 affecting the first noncoding exon while leaving the coding regions intact. Review of the literature shows that this is the smallest 5' deletion affecting only the noncoding exons of ANKRD11. Real-time polymerase chain reaction demonstrated that the copy number variant was not present in either of the proband's parents, suggesting it occurred de novo. RNA expression analysis demonstrated significantly decreased transcript abundance compared to controls. This provides new evidence for haploinsufficiency as a mechanism of disease in KBG syndrome.

Clinical description, molecular delineation and genotype–phenotype correlation in 340 patients with KBG syndrome: addition of 67 new patients

Background

KBG syndrome is a highly variable neurodevelopmental disorder and clinical diagnostic criteria have changed as new patients have been reported. Both loss-of-function sequence variants and large deletions (copy number variations, CNVs) involvingANKRD11cause KBG syndrome, but no genotype–phenotype correlation has been reported.

Methods

67 patients with KBG syndrome were assessed using a custom phenotypical questionnaire. Manifestations present in >50% of the patients and a ‘phenotypical score’ were used to perform a genotype–phenotype correlation in 340 patients from our cohort and the literature.

Results

Neurodevelopmental delay, macrodontia, triangular face, characteristic ears, nose and eyebrows were the most prevalentf (eatures. 82.8% of the patients had at least one of seven main comorbidities: hearing loss and/or otitis media, visual problems, cryptorchidism, cardiopathy, feeding difficulties and/or seizures. Associations found included a higher phenotypical score in patients with sequence variants compared with CNVs and a higher frequency of triangular face (71.1% vs 42.5% in CNVs). Short stature was more frequent in patients with exon 9 variants (62.5% inside vs 27.8% outside exon 9), and the prevalence of intellectual disability/attention deficit hyperactivity disorder/autism spectrum disorder was lower in patients with the c.1903_1907del variant (70.4% vs 89.4% other variants). Presence of macrodontia and comorbidities were associated with larger deletion sizes and hand anomalies with smaller deletions.

Conclusion

We present a detailed phenotypical description of KBG syndrome in the largest series reported to date of 67 patients, provide evidence of a genotype–phenotype correlation between some KBG features and specificANKRD11variants in 340 patients, and propose updated clinical diagnostic criteria based on our findings.

Natural history of KBG syndrome in a large European cohort

KBG syndrome (KBGS) is characterized by distinctive facial gestalt, short stature and variable clinical findings. With ageing, some features become more recognizable, allowing a differential diagnosis. We aimed to better characterize natural history of KBGS. In the context of a European collaborative study, we collected the largest cohort of KBGS patients (49). A combined array- based Comparative Genomic Hybridization and next generation sequencing (NGS) approach investigated both genomic Copy Number Variants and SNVs. Intellectual disability (ID) (82%) ranged from mild to moderate with severe ID identified in two patients. Epilepsy was present in 26.5%. Short stature was consistent over time, while occipitofrontal circumference (median value: -0.88 SD at birth) normalized over years. Cerebral anomalies, were identified in 56% of patients and thus represented the second most relevant clinical feature reinforcing clinical suspicion in the paediatric age when short stature and vertebral/dental anomalies are vague. Macrodontia, oligodontia and dental agenesis (53%) were almost as frequent as skeletal anomalies, such as brachydactyly, short fifth finger, fifth finger clinodactyly, pectus excavatum/carinatum, delayed bone age. In 28.5% of individuals, prenatal ultrasound anomalies were reported. Except for three splicing variants, leading to a premature termination, variants were almost all frameshift. Our results, broadening the spectrum of KBGS phenotype progression, provide useful tools to facilitate differential diagnosis and improve clinical management. We suggest to consider a wider range of dental anomalies before excluding diagnosis and to perform a careful odontoiatric/ear-nose-throat (ENT) evaluation in order to look for even submucosal palate cleft given the high percentage of palate abnormalities. NGS approaches, following evidence of antenatal ultrasound anomalies, should include ANKRD11.

A case of prenatal diagnosis of 16q24.3 microdeletion KBG syndrome and review of the literature

Here we report a case of a 16q24.3 microdeletion KBG syndrome (KBGS) in a fetus. The absence of a well-defined phenotype poses a challenge for genetic diagnosis. This report demonstrated that the high-risk chromosome 21 trisomy could be the first manifestation of KBGS, as observed in this case.

Genetic and serum markers in adult degenerative scoliosis: a literature review

STUDY DESIGN

Literature review.

OBJECTIVE

Adult degenerative scoliosis (ADS) is becoming a more prevalent diagnosis with an increasing elderly population. Our objective is to provide a literature review of genetic and serum markers in ADS.

METHODS

A literature review was conducted in the various databases from their inception to July 2020. Studies that reviewed any genetic or serum markers of ADS whether in detection or progression were selected. Studies that reviewed congenital scoliosis or adolescent idiopathic scoliosis (AIS) were excluded.

RESULTS

A total of 1447 titles were identified of which 14 were included in the final review. Two papers reported on serum markers pertaining to serum cartilage metabolites and pentosidine. Twelve studies reported on genetic markers including gene polymorphisms in estrogen receptors, parathyroid hormone receptors, interleukin 6, cyclooxygenase-2 (COX-2), COL2A1, GPRIN1, TRAIL, GRIN receptor, RIMS, LBX1 as well as copy number variations.

CONCLUSIONS

Serum markers of osteoarthritis and sarcopenia have been found to be significantly elevated in ADS patients as well. Numerous polymorphisms have been found in a variety of genes playing key roles in bone formation and regulation. Further research is needed in validating previous studies as well as identifying other biomarkers for patients at risk for developing ADS.

Congenital heart defects in molecularly confirmed KBG syndrome patients

Congenital heart defects (CHDs) are known to occur in 9%-25% of patients with KBG syndrome. In this study we analyzed the prevalence and anatomic types of CHDs in 46 personal patients with KBG syndrome, carrying pathogenetic variants in ANKRD11 or 16q24.3 deletion, and reviewed CHDs in patients with molecular diagnosis of KBG syndrome from the literature. CHD was diagnosed in 15/40 (38%) patients with ANKRD11 variant, and in one patient with 16q24.3 deletion. Left ventricular outflow tract obstructions have been diagnosed in 9/15 (60%), subaortic or muscular ventricular septal defect in 5/15 (33%), dextrocardia in 1/15 (8%). The single patient with 16q24.3 deletion and CHD had complete atrioventricular septal defect (AVSD) with aortic coarctation. Review of KBG patients from the literature and present series showed that septal defects have been diagnosed in 44% (27/61) of the cases, left ventricular tract obstructions in 31% (19/61), AVSD in 18% (11/61). Septal defects have been diagnosed in 78% of total patients with 16q24.3 deletion. Valvar anomalies are frequently diagnosed, prevalently involving the left side of the heart. A distinctive association with AVSD is identifiable and could represent a marker to suggest the diagnosis in younger patients. In conclusion, after precise molecular diagnosis and systematic cardiological screening the prevalence of CHD in KBG syndrome seems to be higher than previously reported in clinical articles. In addition to septal defects, left-sided anomalies and AVSD should be considered. Clinical management of KBG syndrome should include accurate and detailed echocardiogram at time of diagnosis.

Case Report: Two Newly Diagnosed Patients With KBG Syndrome-Two Different Molecular Changes

Mutations or deletions of ANKRD11 gene are responsible for the symptoms of KBG syndrome. The KBG syndrome is a rare genetic disorder which is inherited in an autosomal dominant manner. Affected patients usually have characteristic facial features, macrodontia of the upper central incisors, hand abnormalities, developmental delay and short stature. In the present article we would like to report a clinical and molecular case study of two patients affected by KBG syndrome. The diagnosis of the first patient was confirmed by the identification of the novel pathogenic variant in ANKRD11 gene by next-generation sequencing. The second patient was diagnosed after the detection of a 16q24.2q24.3 deletion encompassing the ANKRD11 gene microarray.

Two Novel Mutations of ANKRD11 Gene and Wide Clinical Spectrum in KBG Syndrome: Case Reports and Literature Review

Background

KBG syndrome (OMIM #148050) is a rare, autosomal dominant inherited genetic disorder caused by heterozygous mutations in the ankyrin repeat domain-containing protein 11 (ANKRD11) gene or by microdeletion of chromosome 16q24.3. It is characterized by macrodontia of the upper central incisors, distinctive facial dysmorphism, short stature, vertebral abnormalities, hand anomaly including clinodactyly, and various degrees of developmental delay. KBG syndrome presents with variable clinical feature and severity among individuals. Here, we report two KBG patients who have different novel heterozygous mutations of ANKRD11 gene with wide range of clinical manifestations.

Case presentation

Two novel heterozygous mutations of ANKRD11 gene were identified in two unrelated Korean patients with variable clinical presentations. The first patient presented with short stature and early puberty and was treated with growth hormone and gonadotropin-releasing hormone agonist without adverse effects. He had mild intellectual disability. In targeted exome sequencing, a novel de novo frameshift variant was identified in ANKRD11, c.5889del, and p. (Ile1963MetfsX9). The second patient had severe intellectual disability with epilepsy. He had normal height and prepubertal stage at the age of 11 years. He had behavioral problems such as autism-like features, anxiety, and stereotypical movements. Whole exome sequencing (WES) was performed, and the novel heterozygous mutation, c3310dup, p. (Glu110GlyfsTer5) in ANKRD11 was identified.

Conclusion

KBG syndrome is often underdiagnosed because of its non-specific features and phenotypic variability. Performing a next—generation sequencing panel, including the ANKRD11 gene for cases of developmental delay with/without short stature may be helpful to identify hitherto undiagnosed KBG syndrome patients.

Novel phenotypes observed in patients with ETV6-linked leukaemia/familial thrombocytopenia syndrome and a biallelic ARID5B risk allele as leukaemogenic cofactor

Background. The phenotypes of patients with the recently discovered, dominant, ETV6-linked leukaemia predisposition and familial thrombocytopenia syndrome are variable, and the exact mechanism of leukaemogenesis remains unclear. Patients and Methods. Here, we present novel clinical and laboratory phenotypes of seven individuals from three families with ETV6 germline mutations and a refined genetic analysis of one child with additional high-hyperdiploid acute lymphoblastic leukaemia (HD-ALL), aiming to elucidate second oncogenic hits. Results. Four individuals from two pedigrees harboured one novel or one previously described variant in the central domain of ETV6 (c.592C>T, p.Gln198* or c.641C>T, p.Pro241Leu, respectively). Neutropenia was an accompanying feature in one of these families that also harboured a variant in RUNX1 (c.1098_1103dup, p.Ile366_Gly367dup), while in the other, an autism-spectrum disorder was observed. In the third family, the index patient suffered from HD-ALL and life-threatening pulmonary mucor mycosis, and had a positive family history of 'immune' thrombocytopenia. Genetic analyses revealed a novel heterozygous mutation in the ETS domain of ETV6 (c.1136T>C, p.Leu379Pro) along with absence of heterozygosity of chromosome (10)(q21.2q21.3), yielding a biallelic leukaemia risk allele in ARID5B (rs7090445-C). The neutrophil function was normal in all individuals tested, and the platelet immune histochemistry of all three pedigrees showed delta-storage-pool defect-like features and cytoskeletal defects. Conclusions. Our clinical observations and results of high-resolution genetic analyses extend the spectrum of possible phenotypes cosegregating with ETV6 germline mutations. Further, we propose ARID5B as potential leukaemogenic cofactor in patients with ETV6-linked leukaemia predisposition and familial thrombocytopenia syndrome.

KBG syndrome: Common and uncommon clinical features based on 31 new patients

KBG syndrome (MIM #148050) is an autosomal dominant disorder characterized by developmental delay, intellectual disability, distinct craniofacial anomalies, macrodontia of permanent upper central incisors, skeletal abnormalities, and short stature. This study describes clinical features of 28 patients, confirmed by molecular testing of ANKRD11 gene, and three patients with 16q24 deletion encompassing ANKRD11 gene, diagnosed in a single center. Common clinical features are reported, together with uncommon findings, clinical expression in the first years of age, distinctive associations, and familial recurrences. Unusual manifestations emerging from present series include juvenile idiopathic arthritis, dysfunctional dysphonia, multiple dental agenesis, idiopathic precocious telarche, oral frenula, motor tics, and lipoma of corpus callosum, pilomatrixoma, and endothelial corneal polymorphic dystrophy. Facial clinical markers suggesting KBG syndrome before 6 years of age include ocular and mouth conformation, wide eyebrows, synophrys, long black eyelashes, long philtrum, thin upper lip. General clinical symptoms leading to early genetic evaluation include developmental delay, congenital malformations, hearing anomalies, and feeding difficulties. It is likely that atypical clinical presentation and overlapping features in patients with multiple variants are responsible for underdiagnosis in KBG syndrome. Improved knowledge of common and atypical features of this disorder improves clinical management.

16q24.3 Microduplication in a Patient With Developmental Delay, Intellectual Disability, Short Stature, and Nonspecific Dysmorphic Features: Case Report and Review of the Literature

We describe the case of a seven-year-old female patient who presented in our service with severe developmental delay, intellectual disability, facial dysmorphism, and femur fracture, observed in the context of very low bone mineral density. Array-based single nucleotide polymorphism (SNP array) analysis identified a 113 kb duplication involving the morbid OMIM genes: ANKRD11 (exon1), RPL13, and PGN genes. ANKRD11 deletions are frequently described in association with KBG syndrome, the duplications being less frequent (one case described before). The exome sequencing was negative for pathogenic variants or of uncertain significance in genes possibly associated with this phenotype. The patient presented subtle signs of KBG syndrome. It is known that the phenotype of KBG syndrome has a wide clinical spectrum, this syndrome being often underdiagnosed due to overlapping features with other conditions, also characterized by multiple congenital anomalies and intellectual disability. The particularity of this case is represented by the very low bone mineral density in a patient with 16q24.3 duplication. ANKRD11 haploinsufficiency is known to be associated with skeletal involvement, such as short stature, or delayed bone age. An effect on bone density has been observed only in experimental studies on mice with induced missense mutations in the ANKRD11 gene. This CNV also involved the duplication of the very conserved RPL13 gene, which could have a role for the skeletal phenotype of this patient, knowing the high level of gene expression in bone tissue and also the association with spondyloepimetaphyseal dysplasia Isidor Toutain type, in case of splicing mutations.

A heterozygous point mutation of the ANKRD11 (c.2579C>T) in a Chinese patient with idiopathic short stature

Background

Pathogenic variants of ANKRD11 have been reported to cause KBG syndrome characterized by short stature, characteristic facial appearance, intellectual disability, macrodontia, and skeletal anomalies. However, the direct clinical relevance of ANKRD11 mutation with short stature is yet unknown.

Methods

Here, we report a Chinese boy with idiopathic short stature (ISS) based on clinical and genetic characteristics. Comprehensive medical evaluations were performed including metabolic studies, endocrine function tests, bone X‐rays, and echocardiography. Whole‐exome and Sanger sequencing was used to detect and confirm genetic mutations associated with short stature in this patient, respectively. The pathogenicity of the variant was further predicted by several in silico prediction tools and repositories of sequence variation. Twenty‐four months follow‐up was performed to observe the growth rate of the patient treated with recombinant human growth hormone (GH).

Results

One heterozygous point mutation (c.2579C>T) was confirmed in the ANKRD11 gene of the patient and inherited from his mother. This mutation site was located within the highly conservative region of ANKRD11 protein and predicted to be possibly damaging in several in silico prediction programs and repositories of sequence variation. Additionally, patient underwent GH replacement therapy for 24 months exhibited good response to the treatment.

Conclusion

A heterozygous point mutation of AKNRD11 gene was identified in a Chinese patient with short stature phenotype. The patient was treated effectively with GH supplementation.

Exploring the behavioral and cognitive phenotype of KBG syndrome

KBG syndrome is a neurodevelopmental disorder, caused by dominant mutations in ANKRD11, that is characterized by developmental delay/intellectual disability, mild craniofacial dysmorphisms, and short stature. Behavior and cognition have hardly been studied, but anecdotal evidence suggests higher frequencies of ADHD‐symptoms and social‐emotional impairments. In this study, the behavioral and cognitive profile of KBG syndrome will be investigated in order to examine if and how cognitive deficits contribute to behavioral difficulties. A total of 18 patients with KBG syndrome and a control group consisting of 17 patients with other genetic disorders with comparable intelligence levels, completed neuropsychological assessment. Age‐appropriate tasks were selected, covering overall intelligence, attention, memory, executive functioning, social cognition and visuoconstruction. Results were compared using Cohen's d effect sizes. As to behavior, fewer difficulties in social functioning and slightly more attentional problems, hyperactivity, oppositional defiant behavior and conduct problems were found in the KBG syndrome group. Regarding cognitive functioning, inspection of the observed differences shows that patients with KBG syndrome showed lower scores on sustained attention, cognitive flexibility, and visuoconstruction. In contrast, the KBG syndrome group demonstrated higher scores on visual memory, social cognition and emotion recognition. The cognitive profile of KBG syndrome in this sample indicates problems in attention and executive functioning that may underlie the behavior profile which primarily comprises impulsive behavior. Contrary to expectations based on previous (case) reports, no deficits were found in social cognitive functioning. These findings are important for counseling purposes, for tailored education planning, and for the development of personalized intervention.

Novel Mutations and Unreported Clinical Features in KBG Syndrome

KBG syndrome is an autosomal dominant disorder caused by pathogenic variants within ANKRD11 or deletions of 16q24.3 which include ANKRD11. It is characterized by distinctive facial features, developmental delay, short stature, and skeletal anomalies. We report 12 unrelated patients where a clinical diagnosis of KBG was suspected and confirmed by targeted analyses. Nine patients showed a point mutation in ANKRD11 (none of which were previously reported) and 3 carried a 16q24.3 deletion. All patients presented with typical facial features and macrodontia. Skeletal abnormalities were constant, and the majority of patients showed joint stiffness. Three patients required growth hormone treatment with a significant increase of height velocity. Brain malformations were identified in 8 patients. All patients showed behavioral abnormalities and most had developmental delay. Two patients had hematological abnormalities. We emphasize that genetic analysis of ANKRD11 can easily reach a detection rate higher than 50% thanks to clinical phenotyping, although it is known that a subset of ANKRD11-mutated patients show very mild features and will be more easily identified through the implementation of gene panels or exome sequencing. Joint stiffness was reported previously in few patients, but it seems to be a common feature and can be helpful for the diagnosis. Hematological abnormalities could be present and warrant a specific follow-up.

KBG syndrome patient due to 16q24.3 microdeletion presenting with a paratesticular rhabdoid tumor: Coincidence or cancer predisposition?

KBG syndrome is a rare autosomal dominant disorder caused by constitutive haploinsufficiency of the ankyrin repeat domain-containing protein 11 (ANKRD11) being the result of either loss-of-function gene variants or 16q24.3 microdeletions. The syndrome is characterized by a variable clinical phenotype comprising a distinct facial gestalt and variable neurological involvement. ANKRD11 is frequently affected by loss of heterozygosity in cancer. It influences the ligand-dependent transcriptional activation of nuclear receptors and tumor suppressive function of tumor protein TP53. ANKRD11 thus serves as a candidate tumor suppressor gene and it has been speculated that its haploinsufficiency may lead to an increased cancer risk in KBG syndrome patients. While no systematic data are available, we report here on the second KBG syndrome patient who developed a malignancy. At 17 years of age, the patient was diagnosed with a left-sided paratesticular extrarenal malignant rhabdoid tumor. Genetic investigations identified a somatic truncating gene variant in SMARCB1, which was not present in the germline, and a constitutional de novo 16q24.3 microdeletion leading to a loss of the entire ANKRD11 locus. Thus, KBG syndrome was diagnosed, which was in line with the clinical phenotype of the patient. At present, no specific measures for cancer surveillance can be recommended for KBG syndrome patients. However, a systematic follow-up and inclusion of KBG syndrome patients in registries (e.g., those currently established for cancer prone syndromes) will provide empiric data to support or deny an increased cancer risk in KBG syndrome in the future.

The first antenatal diagnosis of KBG syndrome: a microdeletion at chromosome 16q24.2q24.3 containing multiple genes including ANKRD11 associated with the disorder

The loss of ANKRD11 gene confirms the diagnosis of KBG syndrome but does not elucidate the pediatric phenotype providing a counseling challenge. With the expansion of prenatal diagnosis, and the potential to perform whole-exome sequencing antenatally, we must describe the genetic abnormalities, antenatal ultrasound findings, and phenotype concurrently to facilitate counseling.

KBG syndrome

CLINICAL DESCRIPTION

KBG syndrome is characterized by macrodontia of upper central incisors, distinctive craniofacial features such as triangular face, prominent nasal bridge, thin upper lip and synophrys; skeletal findings including short stature, delayed bone age, and costovertebral anomalies; and developmental delay/intellectual disability sometimes associated with seizures and EEG abnormalities. The condition was named KBG syndrome after the initials of the last names of three original families reported in 1975.

EPIDEMIOLOGY

The prevalence of KBG syndrome is not established. There are over 100 patients reported in the literature. It is likely that KBG syndrome is underreported due to incomplete recognition and very mild presentations of the disorder in some individuals. KBG syndrome is typically milder in females.

ETIOLOGY

Causative variants in ANKRD11 have been identified in affected individuals. The vast majority of identified variants are loss of function, which include nonsense and frameshift variants and larger deletions at 16q24.3. Haploinsufficiency appears to be the mechanism of pathogenicity.

GENETIC COUNSELING

Familial and de novo cases have been reported. Causative de novo variants occur approximately one third of the time. Transmission follows an autosomal dominant pattern. The syndrome displays inter- and intra-familial variability.

Audiological findings in a de novo mutation of ANKRD11 gene in KBG syndrome: Report of a case and review of the literature

KBG syndrome is a rare genetic disorder, due to a mutation of ANKRD11, characterized by specific craniofacial dysmorphism, short stature and macrodontia of upper central incisors, intellectual disability and skeletal anomalies. We report a de novo mutation of ANKRD11 gene in a 7-years old girl, affected by KBG syndrome with bilateral conductive hearing loss. The aim of this article was to review the audiological findings of this syndrome.