Natural history of KBG syndrome in a large European cohort

Genetic diseases underlying a spectrum of fetal effusions

OBJECTIVES

Nonimmune hydrops fetalis is well understood to be heterogenous and the common endpoint of many genetic diseases. However, less is known about the prevalence and presenting features of genetic diseases that underlie other types of fetal effusions such as single effusions, leaving uncertainty in clinical practice about optimal approaches to testing and counseling for these pregnancies. We aimed to determine the diagnostic yield of exome sequencing by type of fetal effusion and presence of concurrent structural abnormalities and to identify the unique presenting features of underlying genetic diseases.

STUDY DESIGN

We conducted a prospective cohort study of pregnancies with nonimmune hydrops fetalis and other fetal effusions, with participants enrolled from across the United States. Inclusion criteria were nondiagnostic results of chromosomal microarray and/or karyotype and the presence of at least 1 fetal effusion, including nuchal translucency ≥3.5 mm, cystic hygroma, pleural effusion, pericardial effusion, ascites, and/or skin edema. Exome sequencing was performed by our institution's Clinical Laboratory Improvement Amendments-approved laboratory and results were returned to participants and their providers. Detailed fetal phenotypic data were ascertained and used to inform genetic variant interpretation, including fetal imaging findings (ultrasound, magnetic resonance imaging, and echocardiogram), pathology reports, and laboratory reports. Pregnancies with a variant or variants classified as pathogenic or likely pathogenic were considered diagnostic or positive. The primary outcome was the diagnostic yield of exome sequencing by the type of fetal effusion, with and without concurrent structural abnormalities. Secondary outcomes were the types of fetal effusions observed by category of genetic disease.

RESULTS

In all, 118 pregnancies with nonimmune hydrops fetalis and other effusions underwent exome sequencing and 23% (27/118) had positive (diagnostic) findings. Pregnancies with nonimmune hydrops fetalis with and without concurrent structural abnormalities had diagnostic yields of 21% (9/42) and 40% (6/15), respectively (P=.15). Single effusions such as pleural effusion with and without concurrent structural abnormalities had diagnostic yields of 23% (6/26) and 17% (1/6), respectively (P=.61). The diagnostic yield for increased nuchal translucency or cystic hygroma was significantly greater for pregnancies with concurrent structural abnormalities (42%, 5/12) compared to those without (0%, 0/17, P<.01). We further observed numerous patterns in terms of how genetic diseases present in utero, such as RASopathies and musculoskeletal disorders demonstrating all types of effusions, while other disorders marked by neurodevelopmental delays after birth demonstrated all types of effusions except for nonimmune hydrops fetalis.

CONCLUSION

The diagnostic yield of exome sequencing was high across all types of effusions including single effusions with and without concurrent structural abnormalities, with the exception of isolated increased nuchal translucency or cystic hygroma. Furthermore, we observed numerous patterns in terms of how genetic diseases present in utero with fetal effusions. These findings contribute important information for counseling and clinical management, highlight the utility of exome sequencing for fetal effusions beyond nonimmune hydrops fetalis, and inform accurate results of phenotype-driven tests such as exome sequencing.

Life Beyond Childhood: Insight Into the Lived Experience of 91 Adults With KBG Syndrome Through an Online Patient/Caregiver-Reported Co-Produced Questionnaire

PURPOSE

KBG syndrome (KBGS) is a rare neurodevelopmental syndrome. We aimed to study the impact of KBGS in adulthood as reported by individuals with KBGS and their families/caregivers, thereby exploring aspects of everyday life underreported by healthcare professionals.

METHODS

We co-produced an online questionnaire for adults with KBGS and their families/caregivers. Participants were recruited via the KBG Foundation, an American-based charity supporting individuals with KBGS and their families worldwide, and other international collaborators.

RESULTS

There were 91 responses for analysis, across the age range of 16-86 years. Respondents described a range of living arrangements, education, employment, leisure activities, and relationships. A higher proportion of 45-54year-olds had achieved independent living skills such as driving and grocery shopping compared to the younger age groups. None of the participants who were experiencing seizures lived independently. We described high rates of psychiatric comorbidities, behavioral difficulties, sleep problems, seizures, visual and hearing problems, dental and skeletal issues, and a higher than expected cardiovascular and gastrointestinal burden of disease.

CONCLUSION

This study provides new insights into the everyday life of adults with KBGS, along with high rates of comorbidities that continue to impact quality of life into adulthood, with implications for medical care.

Prenatal Diagnosis of KBG Syndrome: Phenotypic and Genotypic Features of 12 Fetal Cases With the Disorder

OBJECTIVE

To present prenatal sonographic features, genomic results, and pregnancy outcomes of fetuses with KBG syndrome (KBGS).

METHOD

This was a retrospective study of 12 cases with KBGS diagnosed by prenatal ultrasound and confirmed by genetic testing. Clinical and laboratory data were collected for these cases, including maternal demographics, prenatal sonographic findings, molecular test results, and pregnancy outcomes.

RESULTS

Twelve cases of KBGS were diagnosed prenatally with confirmatory genetic testing. Five had an abnormal first-trimester ultrasound with increased nuchal translucency (NT). Seven cases had a normal first-trimester ultrasound. Among these, four had mild ventriculomegaly in the second or third trimester, one had an arachnoid cyst found at 22 weeks, one had umbilical-systemic shunt, ventriculomegaly and polyhydramnios found at 24 weeks, and one presented with fetal growth restriction at 30 weeks. Four pregnancies continued to term, and infants presented with the classic phenotype of KBGS at a follow-up of 12 months. All ANKRD11 alterations in the 12 cases were de novo, and were characterized as either deletions encompassing ANKRD11 or loss-of-function variants.

CONCLUSION

Increased NT and mild ventriculomegaly are two common sonographic features of fetal KBGS. Prenatal diagnosis of KBGS can be achieved with ultrasound and comprehensive molecular testing.

Genome scan reveals several loci associated with torus palatinus

OBJECTIVE

Torus Palatinus (TP) is a common trait with an unclear aetiology. Although prior studies suggest a hereditary component, the genetic factors that influence TP risk remain unknown. The purpose of this study is to identify genetic variants associated with TP.

MATERIALS AND METHODS

We assessed the TP status of 829 individuals from various ancestral backgrounds using 3D palate scans. We then carried out a genome-wide association study (GWAS) to identify common variants associated with TP. We also performed gene-based tests across the exome to investigate the role of low-frequency coding variants.

RESULTS

Our GWAS did not identify any genome-wide significant signals but identified suggestive associations including hits on chromosomes 2, 5 and 17 with p-values less than 5 × 10-6. Candidate genes at these suggestive loci have been implicated in normal-range craniofacial features, syndromes with facial and oral malformations, and bone density. We did not find evidence that low-frequency coding variants influence TP risk. In addition, we failed to replicate associations identified in prior genetic studies of TP.

CONCLUSION

These findings suggest that multiple genes likely influence the development of TP. Independent replication will be required to confirm our suggestive associations.

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.

Prenatal exome sequencing, a powerful tool for improving the description of prenatal features associated with genetic disorders

OBJECTIVE

Prenatal exome sequencing (pES) is now commonly used in clinical practice. It can be used to identifiy an additional diagnosis in around 30% of fetuses with structural defects and normal chromosomal microarray analysis (CMA). However, interpretation remains challenging due to the limited prenatal data for genetic disorders.

METHOD

We conducted an ancillary study including fetuses with pathogenic/likely pathogenic variants identified by trio-pES from the "AnDDI-Prenatome" study. The prenatal phenotype of each patient was categorized as typical, uncommon, or unreported based on the comparison of the prenatal findings with documented findings in the literature and public phenotype-genotype databases (ClinVar, HGMD, OMIM, and Decipher).

RESULTS

Prenatal phenotypes were typical for 38/56 fetuses (67.9%). For the others, genotype-phenotype associations were challenging due to uncommon prenatal features (absence of recurrent hallmark, rare, or unreported). We report the first prenatal features associated with LINS1 and PGM1 variants. In addition, a double diagnosis was identified in three fetuses.

CONCLUSION

Standardizing the description of prenatal features, implementing longitudinal prenatal follow-up, and large-scale collection of prenatal features are essential steps to improving pES data interpretation.

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.

Care pathways in childhood neurodevelopmental disorders: Toward greater awareness of KBG syndrome among pediatricians

INTRODUCTION

KBG syndrome is an autosomal dominant, polymalformative genetic syndrome that is mainly associated with neurodevelopmental and learning disorders, intellectual disability, behavioral disorders, and epilepsy as well as characteristic dysmorphic features, short stature, and ENT (ear, nose, and throat) abnormalities. However, the diagnostic pathway of these individuals is an element that has not been broadly evaluated. The main aim of this study was therefore to characterize the diagnostic pathway for these individuals, by assessing the different healthcare professionals involved and the main referral elements.

METHOD

This was a multicenter, retrospective, descriptive study. A cohort of 30 individuals with KBG syndrome who were followed up at Poitiers University Hospital and Bordeaux University Hospital we recruited.

RESULTS

Pediatricians were the main healthcare professionals who referred individuals for genetic consultation, and the main reason for referral was an assessment of learning delays or intellectual disability, in association with other abnormalities.

CONCLUSION

Pediatricians play a crucial role in the diagnostic guidance of individuals with KBG syndrome, and the main reason for referral remains the assessment of a learning delay or intellectual disability. Healthcare professionals must therefore remain attentive to the child's development and the various anomalies associated with it, in particular characteristic dysmorphic features, behavioral disorders, and statural growth.

Functional investigation of a novel ANKRD11 frameshift variant identified in a Chinese family with KBG syndrome

KBG syndrome is a rare autosomal dominant condition characterized by multisystem developmental disorder, primarily caused by loss-of-function variants in ankyrin repeat domain-containing protein 11 (ANKRD11). Approximately 80 % of ANKRD11 variants associated with KBG syndrome, are frameshift and nonsense variants. Current insight into the pathogenesis of KBG syndrome resulting from ANKRD11 truncating variants remains limited. Here, we presented two members from a non-consanguineous Chinese pedigree both exhibiting characteristics fitting the KBG syndrome-associated phenotypic spectrum. Whole-exome sequencing identified a novel heterozygous frameshift variant in ANKRD11 (NM_013275.6, c.2280_2281delGT, p.Y761Qfs*20) in the proband. Sanger sequencing confirmed that the variant was inherited from her mother and co-segregated with KBG syndrome phenotype. In vitro functional assays revealed that the frameshift variant escaped nonsense-mediated mRNA decay, and resulting in a truncated protein with significantly increased expression levels compared to full-length ANKRD11. Immunofluorescence results demonstrated that truncated protein was predominantly expressed in the nucleus of HEK293 cells, while wild-type ANKRD11 was equally distributed in both the nucleus and cytoplasm. Moreover, the truncated protein significantly reduced CDKN1A/P21-promoter luciferase activity in comparison to wild-type ANKRD11 protein, as well as a remarkably decrease in the endogenous CDKN1A/P21 mRNA level in HEK293 cells. These findings suggest a loss of transcriptional activation function and potentially a dominant-negative mechanism. Overall, our study expands the mutational spectrum of ANKRD11 gene and provides new insights into the pathogenic mechanism of KBG syndrome caused by ANKRD11 truncating variants.

Epilepsy in KBG Syndrome: Report of Additional Cases

BACKGROUND

KBG syndrome is a genetic disorder characterized by short stature, dysmorphic features, macrodontia, cognitive impairment, and limb anomalies. Epilepsy is an important comorbidity associated with KBG syndrome, although the entire phenotypic spectrum may not be fully appreciated.

METHODS

We identified five new patients with KBG syndrome-related epilepsy and compared their phenotype to previously reported cases in the literature.

RESULTS

Five patients with KBG syndrome-related epilepsy were identified. Three patients (60%) were male. Median age of seizure onset was 18 months (interquartile range 5, 32). The epilepsy type was generalized in three patients (60%); in two, the epilepsy type was combined (40%), with focal and generalized seizures. In one patient (20%), the epilepsy syndrome was classifiable and the child was diagnosed with myoclonic-atonic epilepsy. All five patients had pathogenic variants in the ANKRD11 gene. Epilepsy was refractory in two patients (40%). No specific antiseizure medication (ASM) was found to be superior. Literature review yielded 134 cases, median age of seizure onset was 4 years, and seizures were generalized (n = 60, 44%), focal (n = 26, 19%), or combined (n = 13, 10%). An epilepsy syndrome was diagnosed in 12 patients (8.8%). In those with documented response to ASM (n = 49), 22.4% were refractory (n = 11).

CONCLUSIONS

Our study confirms that few patients with epilepsy and KBG syndrome have an identifiable epilepsy syndrome and generalized seizures are most common. We highlight that epilepsy associated with KBG syndrome may occur before age one year and should be an important diagnostic consideration in this age group.

Epileptic dyskinetic encephalopathy in KBG syndrome: Expansion of the phenotype

KBG syndrome is characterised by developmental delay, dental (macrodontia of upper central incisors), craniofacial and skeletal anomalies. Since the identification of variants in the gene (ANKRD11) responsible for KBG syndrome, wider phenotypes are emerging. While there is phenotypic variability within many features of KBG syndrome, epilepsy is not usually markedly severe and movement disorders largely undocumented. Here we describe a novel early onset phenotype of dyskinetic epileptic encephalopathy in a male, who presented during infancy with a florid hyperkinetic movement disorder and developmental regression. Initially he had epileptic spasms and tonic seizures, and EEGs revealed a modified hypsarrhythmia. The epilepsy phenotype evolved to Lennox-Gastaut syndrome with seizures resistant to multiple anti-seizure therapies and the movement disorder evolved to choreoathetosis of limbs and head with oro-lingual dyskinesias. Previous extensive neurometabolic and imaging investigations, including panel-based exome sequencing were unremarkable. Later trio exome sequencing identified a de novo pathogenic heterozygous frameshift deletion of ANKRD11 (c.6792delC; p.Ala2265Profs*72). Review of the literature did not identify any individuals with such a hyperkinetic movement disorder presentation in combination with early-onset epileptic encephalopathy. This report expands the phenotype of ANKRD11-related KBG syndrome to include epileptic dyskinetic encephalopathy.

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.

Documentation and prevalence of prenatal and neonatal outcomes in a cohort of individuals with KBG syndrome

Ankyrin Repeat Domain 11 (ANKRD11) gene mutations are associated with KBG syndrome, a developmental disability that affects multiple organ systems. The function of ANKRD11 in human growth and development is not clear, but gene knockout or mutation are lethal in mice embryos and/or pups. In addition, it plays a vital role in chromatin regulation and transcription. Individuals with KBG syndrome are often misdiagnosed or remain undiagnosed until later in life. This is largely due to KBG syndrome's varying and nonspecific phenotypes as well as a lack of accessible genetic testing and prenatal screening. This study documents perinatal outcomes for individuals with KBG syndrome. We obtained data from 42 individuals through videoconferences, medical records, and emails. 45.2% of our cohort was born by C-section, 33.3% had a congenital heart defect, 23.8% were born prematurely, 23.8% were admitted to the NICU, 14.3% were small for gestational age, and 14.3% of the families had a history of miscarriage. These rates were higher in our cohort compared to the overall population, including non-Hispanic and Hispanic populations. Other reports included feeding difficulties (21.4%), neonatal jaundice (14.3%), decreased fetal movement (7.1%), and pleural effusions in utero (4.7%). Comprehensive perinatal studies about KBG syndrome and updated documentation of its phenotypes are important in ensuring prompt diagnosis and can facilitate correct management.

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.

KBG syndrome: Clinical features and molecular findings in seven unrelated Korean families with a review of the literature

BACKGROUND

KBG syndrome is a rare genetic disorder involving macrodontia of the upper central incisors, craniofacial, skeletal, and neurologic symptoms, caused either by a heterozygous variant in ANKRD11 or deletion of 16q24.3, including ANKRD11. Diagnostic criteria were proposed in 2007 based on 50 cases, but KBG syndrome remains underdiagnosed.

METHODS

Whole exome sequencing (WES) and array comparative genomic hybridization (array CGH) were conducted for genetic analysis and patient phenotypes were characterized based on medical records.

RESULTS

Eight patients from seven unrelated families were confirmed with KBG syndrome. All patients (8/8, 100%) had some degree of craniofacial dysmorphism and developmental delay or intellectual disabilities. Triangular face, synophrys, anteverted nostril, prominent ears, long philtrum, and tented upper lip, which are typical facial dysmorphism findings in patients with KBG syndrome, were uniformly identified in the eight patients participating in this study, with co-occurrence rates of 4/8 (50%), 4/8 (50%), 4/8 (50%), 4/8 (50%), 5/8 (62.5%), and 5/8 (62.5%), respectively. Various clinical manifestations not included in the diagnostic criteria were observed. Six patients had point mutations in ANKRD11, one had an exonic deletion of ANKRD11, and one had a 16q24.3 microdeletion. According to the ACMG guidelines, all mutations were classified as pathogenic. The c.2454dup (p.Asn819fs*1) mutation in Pt 4 was reported previously. The remaining variants (c.397 + 1G>A, c.226 + 1G>A, c.2647del (p.Glu883Argfs*94), and c.4093C>T (p.Arg1365Ter)) were novel.

CONCLUSION

The clinical and molecular features of eight patients from seven unrelated Korean families with KBG syndrome described here will assist physicians in understanding this rare genetic condition.