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

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.

New Genetic Diagnoses of Short Stature Provide Insights into Local Regulation of Childhood Growth

Idiopathic short stature is a common condition with a heterogeneous etiology. Advances in genetic methods, including genome sequencing techniques and bioinformatics approaches, have emerged as important tools to identify the genetic defects in families with monogenic short stature. These findings have contributed to the understanding of growth regulation and indicate that growth plate chondrogenesis, and therefore linear growth, is governed by a large number of genes important for different signaling pathways and cellular functions, including genetic defects in hormonal regulation, paracrine signaling, cartilage matrix, and fundamental cellular processes. In addition, mutations in the same gene can cause a wide phenotypic spectrum depending on the severity and mode of inheritance of the mutation.
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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.

Needle breakage during an inferior alveolar nerve block in a child with KBG syndrome: A case report

BACKGROUND

Needle breakage during the administration of dental analgesia is an extremely rare event.

CASE REPORT

A case of needle breakage during the administration of an inferior alveolar nerve block occurred in a child with KBG syndrome. During the injection, a sudden movement of the child caused the breakage of the needle. The next day, the retrieval of the needle was performed surgically under general analgesia.

FOLLOW-UP

Three months after the surgery the healing was good. Two years later the child underwent a dental extraction with the aid of nitrous oxide/oxygen analgesia/anxiolysis.

CONCLUSION

Needle fracture is a possible event during the administration of dental analgesia in children.

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.

Intellectual Profiles in KBG-Syndrome: A Wechsler Based Case-Control Study

KBG syndrome is a neurodevelopmental disorder (NDD) caused by loss-of-function of the ANKRD11 gene. The core phenotype comprises developmental delay (DD)/ intellectual disability (ID) and several specific facial dysmorphisms. In addition, both ADHD- and ASD-related symptoms have been mentioned. For the correct understanding of these developmental and behavioral characteristics however, it is of great importance to apply objective measures, which seldom has been done in patients with KBG syndrome. In this study, intelligence profiles of patients with KBG syndrome (n = 18) were compared with a control group comprising patients with NDD caused by various other genetic defects (n = 17), by means of the Wechsler scales. These scales were also used to measure speed of information processing, working memory, verbal comprehension and perceptual reasoning. No significant differences were found in the global level of intelligence of patients with KBG syndrome as compared to the patient genetic control group. The same was true for Wechsler subtest results. Hence, behavioral problems associated with KBG syndrome cannot directly be related to or explained by a specific intelligence profile. Instead, specific assessment of neurocognitive functions should be performed to clarify the putative behavioral problems as observed in this syndrome.

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.

KBG syndrome involving a single-nucleotide duplication in ANKRD11

KBG syndrome is a rare autosomal dominant genetic condition characterized by neurological involvement and distinct facial, hand, and skeletal features. More than 70 cases have been reported; however, it is likely that KBG syndrome is underdiagnosed because of lack of comprehensive characterization of the heterogeneous phenotypic features. We describe the clinical manifestations in a male currently 13 years of age, who exhibited symptoms including epilepsy, severe developmental delay, distinct facial features, and hand anomalies, without a positive genetic diagnosis. Subsequent exome sequencing identified a novel de novo heterozygous single base pair duplication (c.6015dupA) in ANKRD11, which was validated by Sanger sequencing. This single-nucleotide duplication is predicted to lead to a premature stop codon and loss of function in ANKRD11, thereby implicating it as contributing to the proband's symptoms and yielding a molecular diagnosis of KBG syndrome. Before molecular diagnosis, this syndrome was not recognized in the proband, as several key features of the disorder were mild and were not recognized by clinicians, further supporting the concept of variable expressivity in many disorders. Although a diagnosis of cerebral folate deficiency has also been given, its significance for the proband's condition remains uncertain.

KBG syndrome: An Australian experience

In 2011, heterozygous mutations in the ANKRD11 gene were identified in patients with KBG syndrome. Since then, 100 cases have been described with the expansion of the clinical phenotype. Here we present 18 KBG affected individuals from 13 unrelated families, 16 with pathogenic mutations in the ANKRD11 gene. Consistent features included intellectual disability, macrodontia, and the characteristic broad forehead with hypertelorism, and a prominent nasal bridge. Common features included hand anomalies, cryptorchidism, and a large number of palate abnormalities. Distinctive findings in this series included malrotation of the abdominal viscera, bilateral inguinal herniae in two patients, basal ganglia calcification and the finding of osteopenia in three patients. Nine novel heterozygous variants were found and the genotype-phenotype correlation was explored. This report highlights the need for thorough examination and investigation of the dental and skeletal systems. The results confirm the specificity of ANKRD11 mutations in KBG and further evidence for this transcription repressor in neural, cardiac, and skeletal development. The description of further cases of KBG syndrome is needed to further delineate this condition, in particular the specific neurological and behavioral phenotype.