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.     

Clinical and genetic aspects of KBG syndrome

KBG syndrome is characterized by short stature, distinctive facial features, and developmental/cognitive delay and is caused by mutations in ANKRD11, one of the ankyrin repeat‐containing cofactors. We describe 32 KBG patients aged 2–47 years from 27 families ascertained via two pathways: targeted ANKRD11 sequencing (TS) in a group who had a clinical diagnosis of KBG and whole exome sequencing (ES) in a second group in whom the diagnosis was unknown. Speech delay and learning difficulties were almost universal and variable behavioral problems frequent. Macrodontia of permanent upper central incisors was seen in 85%. Other clinical features included short stature, conductive hearing loss, recurrent middle ear infection, palatal abnormalities, and feeding difficulties. We recognized a new feature of a wide anterior fontanelle with delayed closure in 22%. The subtle facial features of KBG syndrome were recognizable in half the patients. We identified 20 ANKRD11 mutations (18 novel: all truncating) confirmed by Sanger sequencing in 32 patients. Comparison of the two ascertainment groups demonstrated that facial/other typical features were more subtle in the ES group. There were no conclusive phenotype–genotype correlations. Our findings suggest that mutation of ANKRD11 is a common Mendelian cause of developmental delay. Affected patients may not show the characteristic KBG phenotype and the diagnosis is therefore easily missed. We propose updated diagnostic criteria/clinical recommendations for KBG syndrome and suggest that inclusion of ANKRD11 will increase the utility of gene panels designed to investigate developmental delay. © 2016 The Authors. American Journal of Medical Genetics Part A Published by Wiley Periodicals, Inc.

     

A Chinese patient with KBG syndrome and a 9q31.2–33.1 microdeletion

KBG syndrome is characterized by postnatal short stature, macrodontia, facial and hand anomalies, delayed bone age and intellectual disability. KBG syndrome is an infrequently reported autosomal dominant condition caused by a mutation or haploinsufficiency of ANKRD11 at 16q24.3. We report on a patient, who showed many manifestations of KBG syndrome and was found to harbor a de novo ANKRD11 mutation, c.362T > A (p.Met121Lys). As the patient showed additional characteristics not occurring in KBG syndrome, a CGH array was performed which showed a de novo microdeletion of 9q31.2–q33.1. The majority of findings in our patient can be explained by the combined ANKRD11 mutation and 9q31.2–33.1 deletion. The case demonstrates well the need for comparing an abnormal genotype with a detailed phenotype analysis and the need for further studies in case the phenotype is unusual for the genotype.     

Familial 16q24.3 microdeletion involving ANKRD11 causes a KBG-like syndrome

Haploinsufficiency of ANKRD11 encoding ankyrin repeat domain-containing protein 11 was recently reported as the cause of a syndrome due to microdeletion, characterized by intellectual disability with minor facial anomalies and short stature. Most recently, intragenic mutations of ANKRD11 were found in a cohort of patients with KBG syndrome. KBG is an autosomal dominant intellectual disability syndrome characterized by short stature, characteristic facial appearance, macrodontia, and skeletal anomalies. It remains unknown if deletion of the entire ANKRD11 causes KBG syndrome. We present a mother and child with a heterozygous 365?Kb deletion at 16q24.3 containing ANKRD11, ZNF778, and SPG7 genes. The child presented with developmental delay, facial anomalies, hand anomalies, and a congenital heart defect. The mother has short stature, facial anomalies, macrodontia, hand anomalies, and learning disability. Both individuals had many findings reported in KBG syndrome and the family met the suggested diagnostic criteria. However, typical macrodontia with fused incisors, costovertebral anomalies, and delayed bone age were not present. We conclude that microdeletions involving ANKRD11 result in a phenotype similar to that of KBG syndrome. ? 2012 Wiley Periodicals, Inc.     

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. © 2013 Wiley Periodicals, Inc.     

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. © 2012 Wiley Periodicals, Inc.     

Broadening of cohesinopathies: exome sequencing identifies mutations in ANKRD11 in two patients with Cornelia de Lange‐overlapping phenotype

Cornelia de Lange syndrome (CdLS) and KBG syndrome are two distinct developmental pathologies sharing common features such as intellectual disability, psychomotor delay, and some craniofacial and limb abnormalities. Mutations in one of the five genes NIPBL, SMC1A, SMC3, HDAC8 or RAD21, were identified in at least 70% of the patients with CdLS. Consequently, additional causative genes, either unknown or responsible of partially merging entities, possibly account for the remaining 30% of the patients. In contrast, KBG has only been associated with mutations in ANKRD11. By exome sequencing we could identify heterozygous loss‐of‐function mutations in ANKRD11 in two patients with the clinical diagnosis of CdLS. Both patients show features reminiscent of CdLS such as characteristic facies as well as a small head circumference which is not described for KBG syndrome. Patient A, who carries the mutation in a mosaic state, is a 4‐year‐old girl with features reminiscent of CdLS. Patient B, a 15‐year‐old boy, shows a complex phenotype which resembled CdLS during infancy, but has developed to a more KBG overlapping phenotype during childhood. These findings point out the importance of screening ANKRD11 in young CdLS patients who were found to be negative for mutations in the five known CdLS genes.     

Prominent and elongated coccyx,a new manifestation of KBG syndrome associated with novel mutation in ANKRD11

KBG syndrome is characterized by short stature, distinctive facial features, and developmental/cognitive delay and is caused by mutations in ANKRD11, one of the ankyrin repeat‐containing cofactors. After the advent of whole exome sequencing, the number of clinical reports with KBG diagnosis has increased, leading to a revision of the phenotypic spectrum associated with this syndrome. Here, we report a female child showing clinical features of the KBG syndrome in addition to a caudal appendage at the coccyx with prominent skin fold and a peculiar calcaneus malformation. Exons and exon–intron junctions targeted resequencing of SH3PXD2B and MASP1 genes, known to be associated with prominent coccyx, gave negative outcome, whereas sequencing of ANKRD11 whose mutations matched the KBG phenotype of the proband showed a de novo heterozygous frameshift variant c.4528_4529delCC in exon 9 of ANKRD11. This report contributes to expand the knowledge of the clinical features of KBG syndrome and highlights the need to search for vertebral anomalies and suspect this condition in the presence of a prominent, elongated coccyx.     

KBG syndrome in two patients from Egypt

KBG syndrome is an intellectual disability (ID) associated with multiple congenital anomalies in which the macrodontia could be the clue for the diagnosis. It is caused either by heterozygous variant in ANKRD11 gene or 16q24.3 microdeletions that involve the ANKRD11 gene. Here, we report on two unrelated male patients who presented with ID, short stature, webbing of neck, and cryptorchidism. Noonan syndrome was suspected first but the presence of macrodontia in both patients pointed to KBG syndrome which was confirmed thereafter by the identification of a novel pathogenic variant in ANKRD11 gene, c.5488G>T (p.E1830*). Macrodontia was noticed in all the deciduous anterior teeth in Patient 1. This observation was reported previously in few patients, but it seems to be a common feature that could be misdiagnosed as premature eruption of teeth. Therefore, our results confirm that maxillary permanent central incisors may not be the only teeth affected in KBG but also all the deciduous teeth. Interestingly, desquamative gingivitis was additionally noted in Patient 1, which has not been reported previously, however; it could be a coincidental finding. To the best of our knowledge, this is the first report from Egypt.     

Tethered cord syndrome in KBG syndrome

Tethered cord syndrome (TCS) is characterized by leg pain and weakness, bladder and bowel dysfunction, orthopedic malformations such as scoliosis, and motor deficits caused by the fixation of the spinal cord to surrounding tissues. TCS is surgically treatable and often found in conjunction with other syndromic conditions. KBG syndrome is caused by variants in the ANKRD11 gene and is characterized by short stature, developmental delay, macrodontia, and a triangular face. The current study explores the prevalence of TCS in pediatric KBG patients and their associated signs and symptoms. Patients with KBG were surveyed for signs and symptoms associated with TCS and asked if they had been diagnosed with the syndrome. We found a high proportion of patients diagnosed with (11%) or being investigated for TCS (24%), emphasizing the need to further characterize the comorbid syndromes. No signs or symptoms clearly emerged as indicative of TCS in KBG patients, but some the prevalence of some signs and symptoms varied by sex. Male KBG patients with diagnosed TCS were more likely to have coordination issues and global delay/brain fog than their female counterparts. Understanding the presentation of TCS in KBG patients is critical for timely diagnosis and treatment.     

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.     

Targeted genetic analysis in a large cohort of familial and sporadic cases of aneurysm or dissection of the thoracic aorta

PurposeThoracic aortic aneurysm/aortic dissection (TAAD) is a disorder with highly variable age of onset and phenotype. We sought to determine the prevalence of pathogenic variants in TAAD-associated genes in a mixed cohort of sporadic and familial TAAD patients and identify relevant genotype–phenotype relationships.MethodsWe used a targeted polymerase chain reaction and next-generation sequencing–based panel for genetic analysis of 15 TAAD-associated genes in 1,025 unrelated TAAD cases.ResultsWe identified 49 pathogenic or likely pathogenic (P/LP) variants in 47 cases (4.9% of those successfully sequenced). Almost half of the variants were in nonsyndromic cases with no known family history of aortic disease. Twenty-five variants were within FBN1 and two patients were found to harbor two P/LP variants. Presence of a related syndrome, younger age at presentation, family history of aortic disease, and involvement of the ascending aorta increased the risk of carrying a P/LP variant.ConclusionGiven the poor prognosis of TAAD that is undiagnosed prior to acute rupture or dissection, genetic analysis of both familial and sporadic cases of TAAD will lead to new diagnoses, more informed management, and possibly reduced mortality through earlier, preclinical diagnosis in genetically determined cases and their family members.     

Screening of VCP mutations in Chinese amyotrophic lateral sclerosis patients

Mutations in valosin-containing protein (VCP) gene have been recently found in familial and sporadic amyotrophic lateral sclerosis (ALS). To define the frequency of VCP mutations in ALS patients in Chinese population, we sequenced all 17 exons of the VCP gene in a cohort of both familial and sporadic ALS patients of Chinese origin. No nonsynonymous coding variants were identified. This indicates that VCP mutations are not a common cause of familial or sporadic ALS in Chinese population.     

Family trio-based sequencing in 404 sporadic bilateral hearing loss patients discovers recessive and De novo genetic variants in multiple ways

Hereditary hearing loss (HL) has high genetic and phenotypical heterogeneity including the overlapping and variable phenotypic features. For sporadic HL without a family history, it is more difficult to indicate the contribution of genetic factors to define a pattern of inheritance. We assessed the contribution of genetic variants and patterns of inheritance by a family trio-based sequencing and provided new insight into genetics. We conducted an analysis of data from unrelated sporadic patients with HL (n = 404) who underwent trio-based whole-exome sequencing (trio-WES) or proband-only WES (p-WES) or targeted exome sequencing (TES), and the samples of their unaffected-parents (n = 808)were validated. A molecular diagnosis was rendered for 191 of 404 sporadic HL patients (47.3%) in multiple modes of inheritance, including autosomal recessive (AR), autosomal dominant (AD) caused by de novo variants, copy-number variants (CNVs), X-linked recessive, and dual genetic diagnosis. Among these patients, 83 (43.5%) cases were diagnosed with variants in rare genes. Sporadic HL patients were identified by multiple modes of transmission. Observed variations in rare genes and multiple modes of inheritance can strikingly emphasize the important etiological contribution of recessive and de novo genetic variants to a large cohort of sporadic HL cases plus their parents.