The KBG syndrome, characteristic dental findings: a case report

Caregiver-reported dental manifestations in individuals with genetic neurodevelopmental disorders

BACKGROUND

Children with neurodevelopmental disorders (NDDs) often have poor oral health and dental abnormalities. An increasing number of genes have been associated with neurodevelopmental conditions affecting the oral cavity, but the specific dental features associated with many genes remain unknown.

AIM

To report the types and frequencies of dental manifestations in children with neurodevelopmental conditions of known genetic cause.

DESIGN

A 30-question survey assesing ectodermal and dental features was administered through Simons Searchlight, with which formed a recontactable cohort of individuals with genetic NDDs often associated with autism spectrum disorder (ASD).

RESULTS

Data were collected from a largely paediatric population with 620 affected individuals across 39 genetic conditions and 145 unaffected siblings without NDDs for comparison. Drooling, difficulty accessing dental care, late primary teeth eruption, abnormal primary and permanent teeth formation, misshapen nails, and hair loss were more frequent in individuals with NDDs. Additionally, we evidenced an association between three new pathogenic gene variant/oral manifestation pairs: CSNK2A1/unusual primary teeth, DYRK1A/late primary teeth eruption, and PPP2R5D/sialorrhea.

CONCLUSION

Our results demonstrate that genetic NDDs caused by mutations in CSNK2A1, DYRK1A, and PP2R5D are associated with unique dental manifestations, and knowledge of these features can be helpful to personalize dental care.

An unusual case of KBG syndrome with unique oral findings

KBG syndrome is a condition characterised by macrodontia, neurological disturbance, short stature, a distinct cranio-facial appearance, and skeletal anomalies. The authors describe what appears to be the first case of KBG syndrome reported from the Indian subcontinent. Meticulous evaluation of the dental findings helps to identify such cases which may otherwise remain undiagnosed. Further research is warranted to determine the classic and variant presentations of this condition, with follow-up data providing valuable insights into its natural history and long-term prognosis.

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.

The KBG syndrome: Case report

Introduction

The KBG syndrome is a rare autosomal dominant condition, first described by Hermann et al. in 1975. Fundamental findings are: mild development delay, short stature, craniofacial dysmorphism and skeletal anomalies.

Case presentation

A 32 years old woman, Caucasian race, weight 57 Kg, affected by KBG syndrome was sent to our clinics for preoperative anaesthesia evaluation. She was schedules for left ossicular reconstruction under general anaesthesia for bilateral hearing loss. A psycho-motor retardation was associated to morphological anomalies such as short neck, hyperlordosis without neck extension imparirment, craniofacial anomalies and dento-skeletal abnormalities. An echocardiography showed the presence of interatrial defect with left-to-right shunt. The patient was sent to a cardiac surgery centre.

Conclusion

Perioperative evaluation of patients affected by KBG syndrome must take into consideration the management of difficult airways, due to the associated craniofacial dysmorphism. The possible presence of cardiac anomalies in the KBG syndrome is currently being evalueted. In this report the finding of cardiomegaly and congestion of the pulmonary circulation was attributed to presence of an interatrial defect with left-to-right shunt. The risk of cardiopulmonary failure led us to ask for a cardiac surgery consult. Perioperative management of these patients should be extremely accurate, even in the case of minor surgery, and should include also chest X-rays and echocardiography evaluation.

Dental agenesis: genetic and clinical perspectives

Dental agenesis is the most common developmental anomaly in humans and is frequently associated with several other oral abnormalities. Whereas the incidence of missing teeth may vary considerably depending on dentition, gender, and demographic or geographic profiles, distinct patterns of agenesis have been detected in the permanent dentition. These frequently involve the last teeth of a class to develop (I2, P2, M3) suggesting a possible link with evolutionary trends. Hypodontia can either occur as an isolated condition (non-syndromic hypodontia) involving one (80% of cases), a few (less than 10%) or many teeth (less than 1%), or can be associated with a systemic condition or syndrome (syndromic hypodontia), essentially reflecting the genetically and phenotypically heterogeneity of the condition. Based on our present knowledge of genes and transcription factors that are involved in tooth development, it is assumed that different phenotypic forms are caused by different genes involving different interacting molecular pathways, providing an explanation not only for the wide variety in agenesis patterns but also for associations of dental agenesis with other oral anomalies. At present, the list of genes involved in human non-syndromic hypodontia includes not only those encoding a signaling molecule (TGFA) and transcription factors (MSX1 and PAX9) that play critical roles during early craniofacial development, but also genes coding for a protein involved in canonical Wnt signaling (AXIN2), and a transmembrane receptor of fibroblast growth factors (FGFR1). Our objective was to review the current literature on the molecular mechanisms that are responsible for selective dental agenesis in humans and to present a detailed overview of syndromes with hypodontia and their causative genes. These new perspectives and future challenges in the field of identification of possible candidate genes involved in dental agenesis are discussed.

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.

Clinical variability in KBG syndrome: report of three unrelated families

The KBG syndrome is characterized by short stature, macrodontia, a specific combination of minor anomalies, developmental delay, and/or mental retardation. We reported on four patients from three unrelated families. The most frequent clinical findings were: atypical face, long/flat philtrum, thin upper lip, macrodontia, dental malposition, enamel hypoplasia, and cleft teeth. Skeletal anomalies such as cervical ribs and vertebral abnormalities were also noted. Hand anomalies were observed in three patients. Mental retardation and developmental delay were present in three of the four patients. There is wide clinical variability in the expression of this syndrome. The males are usually more severely affected then the females, suggesting possible X-linked inheritance in some cases.

KBG syndrome in a cohort of Italian patients

KBG syndrome comprises a distinct facial phenotype, macrodontia, short stature, and skeletal anomalies. So far, it has been reported in 29 individuals. Recently, diagnostic criteria were outlined. Here, we describe eight new patients whose clinical and radiological findings fit the diagnostic criteria of KBG syndrome. While most patients were sporadic in occurrence, in two families the disorder was transmitted from mildly affected mothers to their affected children. The phenotype of KBG syndrome has been reviewed based on published and present patients. EEG anomalies with or without seizures, mixed hearing loss, palatal anomalies with secondary speech disorder, distinct age-related behavior, and cryptorchidism are possible additional characteristics. Less common manisfestations were posterior fossa malformations, eye defects, and congenital heart defects.

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

We report on a Turkish family in which the father and his two sons were diagnosed as having the KBG syndrome. Large upper central incisors were the diagnostic finding in all three patients along with mental retardation, cryptorchidism, skeletal abnormalities, and short stature. Our report clearly confirms that the inheritance is autosomal dominant in KBG syndrome, although a high male to female ratio has been observed in published cases.