The KBG syndrome: confirmation of autosomal dominant inheritance and further delineation of the phenotype

Natural history of adults with KBG syndrome: A physician-reported experience

PURPOSE

KBG syndrome (KBGS) is a rare neurodevelopmental syndrome caused by haploinsufficiency of ANKRD11. The childhood phenotype is extensively reported but limited for adults. Thus, we aimed to delineate the clinical features of KBGS.

METHODS

We collected physician-reported data of adults with molecularly confirmed KBGS through an international collaboration. Moreover, we undertook a systematic literature review to determine the scope of previously reported data.

RESULTS

The international collaboration identified 36 adults from 31 unrelated families with KBGS. Symptoms included mild/borderline intellectual disability (n = 22); gross and/or fine motor difficulties (n = 15); psychiatric and behavioral comorbidities including aggression, anxiety, reduced attention span, and autistic features (n = 26); nonverbal (n = 3), seizures with various seizure types and treatment responses (n = 10); ophthalmological comorbidities (n = 20). Cognitive regression during adulthood was reported once. Infrequent features included dilatation of the ascending aorta (n = 2) and autoimmune conditions (n = 4). Education, work, and residence varied, and the diversity of professional and personal roles highlighted the range of abilities seen. The literature review identified 154 adults reported across the literature, and we have summarized the features across both data sets.

CONCLUSION

Our study sheds light on the long-term neurodevelopmental outcomes, seizures, behavioral and psychiatric features, and education, work, and living arrangements for adults with KBGS.

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.

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.

Large-Scale Functional Assessment of Genes Involved in Rare Diseases with Intellectual Disabilities Unravels Unique Developmental and Behaviour Profiles in Mouse Models

Major progress has been made over the last decade in identifying novel genes involved in neurodevelopmental disorders, although the task of elucidating their corresponding molecular and pathophysiological mechanisms, which are an essential prerequisite for developing therapies, has fallen far behind. We selected 45 genes for intellectual disabilities to generate and characterize mouse models. Thirty-nine of them were based on the frequency of pathogenic variants in patients and literature reports, with several corresponding to de novo variants, and six other candidate genes. We used an extensive screen covering the development and adult stages, focusing specifically on behaviour and cognition to assess a wide range of functions and their pathologies, ranging from basic neurological reflexes to cognitive abilities. A heatmap of behaviour phenotypes was established, together with the results of selected mutants. Overall, three main classes of mutant lines were identified based on activity phenotypes, with which other motor or cognitive deficits were associated. These data showed the heterogeneity of phenotypes between mutation types, recapitulating several human features, and emphasizing the importance of such systematic approaches for both deciphering genetic etiological causes of ID and autism spectrum disorders, and for building appropriate therapeutic strategies.

Growth hormone therapy for children with KBG syndrome: A case report and review of literature

BACKGROUND

The incidence of short stature in KBG syndrome is relatively high. Data on the therapeutic effects of growth hormone (GH) on children with KBG syndrome accompanied by short stature in the previous literature has not been summarized.

CASE SUMMARY

Here we studied a girl with KBG syndrome and collected the data of children with KBG syndrome accompanied by short stature from previous studies before and after GH therapy. The girl was referred to our department because of short stature. Physical examination revealed mild dysmorphic features. The peak GH responses to arginine and clonidine were 6.22 and 5.40 ng/mL, respectively. The level of insulin-like growth factor 1 (IGF-1) was 42.0 ng/mL. Genetic analysis showed a c.2635 dupG (p.Glu879fs) mutation in the ANKRD11 gene. She received GH therapy. During the first year of GH therapy, her height increased by 0.92 standard deviation score (SDS). Her height increased from -1.95 SDS to -0.70 SDS after two years of GH therapy. There were ten children with KBG syndrome accompanied by short stature who received GH therapy in reported cases. Height SDS was improved in nine (9/10) of them. The mean height SDS in five children with KBG syndrome accompanied by short stature increased from -2.72 ± 0.44 to -1.95 ± 0.57 after the first year of GH therapy (P = 0.001). There were no adverse reactions reported after GH treatment.

CONCLUSION

GH treatment is effective in our girl and most children with KBG syndrome accompanied by short stature during the first year of therapy.

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.

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.

Novel ANKRD11 gene mutation in an individual with a mild phenotype of KBG syndrome associated to a GEFS+ phenotypic spectrum: a case report

Background

KBG syndrome is a very rare autosomal dominant disorder, characterized by macrodontia, distinctive craniofacial findings, skeletal findings, post-natal short stature, and developmental delays, sometimes associated with seizures and EEG abnormalities. So far, there have been over 100 cases of KBG syndrome reported.

Case presentation

Here, we describe two sisters of a non-consanguineous family, both presenting generalized epilepsy with febrile seizures (GEFS+), and one with a more complex phenotype associated with mild intellectual disability, skeletal and dental anomalies. Whole exome sequencing (WES) analysis in all the family members revealed a heterozygous SCN9A mutation, p.(Lys655Arg), shared among the father and the two probands, and a novel de novo loss of function mutation in the ANKRD11 gene, p.(Tyr1715*), in the proband with the more complex phenotype. The reassessment of the phenotypic features confirmed that the patient fulfilled the proposed diagnostic criteria for KBG syndrome, although complicated by early-onset isolated febrile seizures. EEG abnormalities with or without seizures have been reported previously in some KBG cases.

The shared variant, occurring in SCN9A, has been previously found in several individuals with GEFS+ and Dravet syndrome.

Conclusions

This report describe a novel de novo variant in ANKRD11 causing a mild phenotype of KGB syndrome and further supports the association of monogenic pattern of SCN9A mutations with GEFS+. Our data expand the allelic spectrum of ANKRD11 mutations, providing the first Brazilian case of KBG syndrome. Furthermore, this study offers an example of how WES has been instrumental allowing us to better dissect the clinical phenotype under study, which is a multilocus variation aggregating in one proband, rather than a phenotypic expansion associated with a single genomic locus, underscoring the role of multiple rare variants at different loci in the etiology of clinical phenotypes making problematic the diagnostic path. The successful identification of the causal variant in a gene may not be sufficient, making it necessary to identify other variants that fully explain the clinical picture. The prevalence of blended phenotypes from multiple monogenic disorders is currently unknown and will require a systematic re-analysis of large WES datasets for proper diagnosis in daily practice.

Clinical and molecular findings in 39 patients with KBG syndrome caused by deletion or mutation of ANKRD11

KBG syndrome, due to ANKRD11 alteration is characterized by developmental delay, short stature, dysmorphic facial features, and skeletal anomalies. We report a clinical and molecular study of 39 patients affected by KBG syndrome. Among them, 19 were diagnosed after the detection of a 16q24.3 deletion encompassing the ANKRD11 gene by array CGH. In the 20 remaining patients, the clinical suspicion was confirmed by the identification of an ANKRD11 mutation by direct sequencing. We present arguments to modulate the previously reported diagnostic criteria. Macrodontia should no longer be considered a mandatory feature. KBG syndrome is compatible with autonomous life in adulthood. Autism is less frequent than previously reported. We also describe new clinical findings with a potential impact on the follow-up of patients, such as precocious puberty and a case of malignancy. Most deletions remove the 5'end or the entire coding region but never extend toward 16q telomere suggesting that distal 16q deletion could be lethal. Although ANKRD11 appears to be a major gene associated with intellectual disability, KBG syndrome remains under-diagnosed. NGS-based approaches for sequencing will improve the detection of point mutations in this gene. Broad knowledge of the clinical phenotype is essential for a correct interpretation of the molecular results. © 2016 Wiley Periodicals, Inc.

Novel Genetic Associations and Range of Phenotypes in Children with Disorders of Sex Development and Neurodevelopment: Insights from the Deciphering Developmental Disorders Study

A range of phenotypes that are associated with disorders of sex development (DSD) may also be encountered in patients with neurodevelopmental delay. In this study we have undertaken a collaborative retrospective review of anonymised phenotypic and genotypic data from the UK-wide Deciphering Developmental Disorders (DDD) study. Our objectives were to determine the frequency and range of DSD phenotypes observed in participants in the DDD study and to identify novel genetic associations. We found that of 7,439 DDD participants, 603 (8%) had at least one genital abnormality. In addition, we found that DSD occurs in 5% of patients with learning difficulties. Causative mutations were found in 13 developmental genes, of which, crucially, 6 had no previous reported association with DSD. Our findings indicate that recognition of these associations should not be overlooked in the management of patients with complex conditions and that exomic sequencing through projects like DDD increases diagnostic yield.

Short Stature in KBG Syndrome: First Responses to Growth Hormone Treatment

BACKGROUND

KBG syndrome is a rare disorder characterized by intellectual disability and associated with macrodontia of the upper central incisors, specific craniofacial findings, short stature and skeletal anomalies. Genetic corroboration of a clinical diagnosis has been possible since 2011, upon identification of heterozygous mutations in or a deletion of the ANKRD11 gene.

METHODS

We summarized the height data of 14 adults and 18 children (age range 2-16 years) with a genetically confirmed diagnosis of KBG syndrome. Two of these children were treated with growth hormones.

RESULTS

Stature below the 3rd centile or -1.88 standard deviation score (SDS) was observed in 72% of KBG children and in 57% of KBG adults. Height below -2.50 SDS was observed in 62% of KBG children and in 36% of KBG adults. The mean SDS of height in KBG children was -2.56 and in KBG adults -2.17. Two KBG children on growth hormone therapy increased their height by 0.6 and 1 SDS within 1 year, respectively. The former also received a gonadotropin-releasing hormone agonist due to medical necessity.

CONCLUSION

Short stature is prevalent in KBG syndrome, and spontaneous catch-up growth beyond childhood appears limited. Growth hormone intervention in short KBG children is perceived as promising.

De novo ANKRD11 and KDM1A gene mutations in a male with features of KBG syndrome and Kabuki syndrome

KBG syndrome is a rare, autosomal dominant disorder caused by mutations or deletions leading to haploinsufficiency for the Ankrin Repeating Domain-Containing protein 11 (ANKRD11) at chromosome 16q24.3. Kabuki syndrome is caused by mutations or deletions of lysine (K)-specific methyltransferase 2D (KMT2D) and lysine-specific methylase 6A (KDM6A). We report on a male with developmental delays, cleft palate, craniofacial dysmorphism, hypotonia, and central nervous system anomalies including diminished white matter with thinning of the corpus callosum. Exome sequencing revealed a de novo mutation in ANKRD11, c.2606_2608delAGA, predicting p.Lys869del and an additional, de novo mutation, c.2353T>C, predicting p.Tyr785His in KDM1A, a gene not previously associated with a human phenotype. We describe this child as the first report of a deleterious sequence variant in KDM1A and hypothesize that his phenotype resulted from the combined effect of both mutations.

Partial deletion of ANKRD11 results in the KBG phenotype distinct from the 16q24.3 microdeletion syndrome

KBG syndrome (OMIM 148050) is a very rare genetic disorder characterized by macrodontia, distinctive craniofacial abnormalities, short stature, intellectual disability, skeletal, and neurologic involvement. Approximately 60 patients have been reported since it was first described in 1975. Recently mutations in ANKRD11 have been documented in patients with KBG syndrome, and it has been proposed that haploinsufficiency of ANKRD11 is the cause of this syndrome. In addition, copy number variation in the 16q24.3 region that includes ANKRD11 results in a variable phenotype that overlaps with KBG syndrome and also includes autism spectrum disorders and other dysmorphic facial features. In this report we present a 2½-year-old African American male with features highly suggestive of KBG syndrome. Genomic microarray identified an intragenic 154 kb deletion at 16q24.3 within ANKRD11. This child's mother was mosaic for the same deletion (present in approximately 38% of cells) and exhibited a milder phenotype including macrodontia, short stature and brachydactyly. This family provides additional evidence that ANKRD11 causes KBG syndrome, and the mild phenotype in the mosaic form suggests that KBG phenotypes might be dose dependent, differentiating it from the more variable 16q24.3 microdeletion syndrome. This family has additional features that might expand the phenotype of KBG syndrome.

Neurobehavioral phenotype observed in KBG syndrome caused by ANKRD11 mutations

KBG syndrome is a rare disease characterized by typical facial dysmorphism, macrodontia of upper central incisors, skeletal abnormalities, and developmental delay. Recently, mutations in ANKRD11 gene have been identified in a subset of patients with KBG syndrome, while a contiguous gene deletion syndrome involving 16q24.3 region (including ANKRD11) was delineated in patients with facial dysmorphism, autism, intellectual disability, and brain abnormalities. Although numerous evidences point to a central causative role of ANKRD11 in the neurologic features of these patients, their neurocognitive and behavior phenotypes are still poorly characterized. Herein, we report the complete neurological and psychiatric features observed in two patients with KBG syndrome due to ANKRD11 mutations. Both patients show intellectual disabilities, severe impairment in communication skills, deficits in several aspects of executive functions and working memory and anxious traits. Their features are compared with those of previously reported patients with KBG syndrome aiding in the delineation of neurocognitive phenotype associated to ANKRD11 mutations.

Mutations in ANKRD11 cause KBG syndrome, characterized by intellectual disability, skeletal malformations, and macrodontia

KBG syndrome is characterized by intellectual disability associated with macrodontia of the upper central incisors as well as distinct craniofacial findings, short stature, and skeletal anomalies. Although believed to be genetic in origin, the specific underlying defect is unknown. Through whole-exome sequencing, we identified deleterious heterozygous mutations in ANKRD11 encoding ankyrin repeat domain 11, also known as ankyrin repeat-containing cofactor 1. A splice-site mutation, c.7570-1G>C (p.Glu2524_Lys2525del), cosegregated with the disease in a family with three affected members, whereas in a simplex case a de novo truncating mutation, c.2305delT (p.Ser769GlnfsX8), was detected. Sanger sequencing revealed additional de novo truncating ANKRD11 mutations in three other simplex cases. ANKRD11 is known to interact with nuclear receptor complexes to modify transcriptional activation. We demonstrated that ANKRD11 localizes mainly to the nuclei of neurons and accumulates in discrete inclusions when neurons are depolarized, suggesting that it plays a role in neural plasticity. Our results demonstrate that mutations in ANKRD11 cause KBG syndrome and outline a fundamental role of ANKRD11 in craniofacial, dental, skeletal, and central nervous system development and function.

KBG syndrome: review of the literature and findings of 5 affected patients

KBG syndrome is a rare, multiple congenital anomaly/mental retardation (MCA/MR) syndrome characterized by neurological disturbance, short stature, a distinct craniofacial appearance, and skeletal anomalies. It is likely to be autosomal dominant in nature with a wide range of expressivity in its clinical features. Dentally, macrodontia, particularly of the maxillary permanent central incisors is a common finding. The aim of this article was to review the familiar clinical presentations of this syndrome and to highlight previously unreported findings of generalized macrodontia and shovel-shaped incisors. Dental and clinical findings of 2 affected brothers with a 3-year follow-up of their dental progress following orthodontic treatment are outlined. Additionally, dental and clinical findings of an affected mother and her daughter, and another sporadic case are also presented.

KBG syndrome: report of twins, neurological characteristics, and delineation of diagnostic criteria

KBG syndrome is a multiple congenital anomaly (MCA) syndrome comprising developmental delay, postnatal short stature, and delayed bone age. Many physical anomalies involving the face, hands, and costovertebral axis have been described in this syndrome. We present twin males with KBG syndrome and a review of 50 published case reports, with particular emphasis on the neurological aspects of KBG syndrome, including seizures, MRI findings, and behavior difficulties. It is argued that diagnostic criteria for KBG syndrome should include neurological involvement, that is, global developmental delay, seizures, and/or mental retardation (MR). The characteristic facial changes and representative hand and costovertebral anomalies are also defined. These diagnostic criteria were obtained from 50 publications and appeared to support the diagnosis in 43 cases. They will be helpful to pediatricians, geneticists, and neurologists in evaluating patients for this condition.

KBG syndrome

KBG syndrome is a rare condition characterised by a typical facial dysmorphism, macrodontia of the upper central incisors, skeletal (mainly costovertebral) anomalies and developmental delay. To date, KBG syndrome has been reported in 45 patients. Clinical features observed in more than half of patients that may support the diagnosis are short stature, electroencephalogram (EEG) anomalies (with or without seizures) and abnormal hair implantation. Cutaneous syndactyly, webbed short neck, cryptorchidism, hearing loss, palatal defects, strabismus and congenital heart defects are less common findings. Autosomal dominant transmission has been observed in some families, and it is predominantly the mother, often showing a milder clinical picture, that transmits the disease. The diagnosis is currently based solely on clinical findings as the aetiology is unknown. The final diagnosis is generally achieved after the eruption of upper permanent central incisors at 7–8 years of age when the management of possible congenital anomalies should have been already planned. A full developmental assessment should be done at diagnosis and, if delays are noted, an infant stimulation program should be initiated. Subsequent management and follow-up should include an EEG, complete orthodontic evaluation, skeletal investigation with particular regard to spine curvatures and limb asymmetry, hearing testing and ophthalmologic assessment.