Alternative titles; symbols
SNOMEDCT: 711156009; ORPHA: 2332; DO: 14780;
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
|---|---|---|---|---|---|---|
| 16q24.3 | KBG syndrome | 148050 | Autosomal dominant | 3 | ANKRD11 | 611192 |
A number sign (#) is used with this entry because of evidence that KBG syndrome (KBGS) is caused by heterozygous mutation in the ANKRD11 gene (611192) on chromosome 16q24.
KBG syndrome (KBGS) is characterized by macrodontia of the upper central incisors, distinctive craniofacial findings, short stature, skeletal anomalies, and neurologic involvement that includes global developmental delay, seizures, and intellectual disability (summary by Sirmaci et al., 2011). Sirmaci et al. (2011) noted that it is likely that KBG syndrome is underdiagnosed, since many of the features, including intellectual disability, are mild, and none of the features is a prerequisite for diagnosis.
Herrmann et al. (1975) described 2 families in which multiple members had short stature, characteristic facies (telecanthus, wide eyebrows, brachycephaly), macrodontia, mental retardation, and skeletal anomalies (abnormal vertebrae, short metacarpals, short femoral necks). Male-to-male transmission occurred in 1 family. The designation 'KBG syndrome' followed Opitz's practice of using the initials of affected families' surnames.
Fryns and Haspeslagh (1984) described what appeared to be the KBG syndrome in 2 sisters and their mother.
Parloir et al. (1977) reported an extensive family segregating KBG syndrome. Soekarman et al. (1994) provided follow-up information on 3 affected brothers reported by Parloir et al. (1977). They had an affected sister, and 3 other brothers, as well as their mother, were said to have partial expression. The adult height of the affected brothers was far below the 3rd centile, with arm spans exceeding stature by at least 9 cm. Relative shortness of the trunk was apparently secondary to mild vertebral skeletal anomalies observed at a young age, with anterior wedging of vertebrae and irregular upper and lower plates. Karyotype was normal male.
Zollino et al. (1994) diagnosed KBG syndrome in 6 sporadic cases. Two of their patients had hypoplasia of cerebellar vermis, 1 had cystic dysplasia of the kidney, and 1 had megalocornea; see 249310.
Devriendt et al. (1998) described the KBG syndrome in a mother and her daughter. At the age of 8 years and 2 months the daughter showed, on x-ray of the skull, very broad unerupted permanent central frontal incisors. The mother had very broad frontal incisors. The daughter had ventricular septal defect, treated surgically. During childhood, she suffered from chronic constipation and recurrent respiratory tract infections. She was retarded with an intelligence quotient of 58 at the age of 8 years. The mother was mildly mentally retarded and had required special education.
Smithson et al. (2000) reported 2 additional cases of KBG syndrome. They suggested that the diagnostic criteria should include hypertelorism, macrodontia, short stature (less than the 10th percentile), delayed bone maturation, skeletal anomalies, and developmental delay (IQ less than 80).
Tekin et al. (2004) reported a family from central Anatolia in which a father and 2 sons had KBG syndrome. All 3 patients had developmental delay and mild to moderate mental retardation. Physical features included short stature (less than 3rd percentile), a triangular face, low anterior and posterior hairlines, bushy eyebrows, large prominent ears, a long philtrum, anteverted nostrils with hypoplastic alae nasi, and wide upper central incisors. The hands were short with clinodactyly, and 1 of the sons had bilateral accessory cervical ribs, thoracic kyphosis, and irregular vertebral arches. The father also had thoracic kyphosis. All 3 men had undescended testes.
Brancati et al. (2004) reviewed 29 cases of the KBG syndrome in the literature and described 8 new patients. Six of the new patients were sporadic in occurrence, but in 2 families the disorder was transmitted from mildly affected mothers to their affected children. EEG anomalies with or without seizures, mixed hearing loss, palatal anomalies with secondary speech disorder, distinct age-related behavior (hyperactivity, anxiety, and poor concentration), and cryptorchidism are possible additional characteristics of the KBG syndrome. Less common manifestations were posterior fossa malformations, eye defects, and congenital heart defects.
Maegawa et al. (2004) diagnosed KBG syndrome in 3 unrelated boys and the mother of 1 of them. In addition to the characteristic macrodontia and dental anomalies, the patients had atypical facies and skeletal anomalies, including hand anomalies in 3 patients. Mental retardation and developmental delay were also present in 3 patients. In the mother-son case, the mother had a milder phenotype.
Skjei et al. (2007) described male twins with KBG syndrome and reviewed 46 published cases. They recommended that 4 or more of the 8 major criteria be present to make the diagnosis of KBG syndrome: macrodontia of the upper central incisors, characteristic facial appearance, hand anomalies, neurologic involvement, bone age 2 standard deviations below the mean, costovertebral anomalies, postnatal short stature, and presence of a first-degree relative with KBG syndrome. Skjei et al. (2007) stated that macrodontia had been observed in over 95% of reported cases but noted that the high frequency might be due to ascertainment bias.
Gnazzo et al. (2020) reported 31 patients with KBG syndrome, including 28 with a heterozygous pathogenic variant in ANKRD11 and 3 with a 16q24 deletion, seen in a single hospital in Italy. The patients ranged in age from 6 months to 23 years. All of the patients had abnormal facial findings, which included wide eyebrows, synophrys, telecanthus, hypertelorism, long black eyebrows, bulbous nose, long prominent philtrum, and thin upper lip. Macrodontia of the central superior incisors was present in 23 patients, and cognitive deficit or learning difficulties were present in 26 patients. Developmental delay was mild or borderline in most patients. Attention deficit hyperactivity disorder was reported in 36% of patients, and behavioral problems were frequent. Congenital heart findings were reported in 11 patients. Eleven patients had feeding difficulties, 21 had hand brachydactyly, and 18 had short stature (less than the 3rd percentile). Less common manifestations (present in under 30% of patients) included velopharyngeal insufficiency in 5, epilepsy in 5, hearing loss in 6, hypertrichosis in 7, and juvenile idiopathic arthritis in 2.
Digilio et al. (2022) analyzed the prevalence and types of congenital heart defects seen in 46 patients with KBG syndrome. Congenital heart defects were present in 15/40 (38%) patients with ANKRD11 pathogenic variants and in 1 of 6 patients (17%) with a 16q24.3 deletion. Among the 15 patients with heart defects and ANKRD11 pathogenic variants, the most common defects were left ventricular outflow tract obstructions in 9 patients (60%), subaortic or muscular ventricular septal defects in 5 patients (33%), and dextrocardia in 1 patient (8%). The single patient with 16q24.3 deletion and congenital heart disease had a complete atrioventricular septal defect with aortic coarctation. Review of KBG patients from the literature and the patients in their series showed that septal defects had been diagnosed in 44%, left ventricular tract obstructions in 31%, and atrioventricular septal defects in 18%. Septal defects were diagnosed in 78% of patients with 16q24.3 deletion. Given the frequent association between atrioventricular septal defects and KBG syndrome, the authors proposed that this heart defect could represent a marker to make a diagnosis of KBG syndrome in younger patients.
Geckinli et al. (2022) described a 9-year-old boy with KBG syndrome. Onset of generalized tonic-clonic seizures occurred at the age of 4 years. After treatment with 2 antiepileptic medications, he had absence seizures associated with fever. He had behavioral issues and learning difficulties. On examination, he had microcephaly, brachycephaly, triangular face, low anterior and posterior hairline, short neck, thick eyebrows, long eyelashes, bulbous nasal tip, long philtrum, thin upper lip, micrognathia, macrodontia of the upper central incisors, brachydactyly, mild clinodactyly of both 5th fingers, transverse crease on the left hand, hallux valgus, and bilateral clinodactyly of the fifth toes. He also had a small intraosseous sclerotic lesion consistent with an enostosis (bone island) in the middle phalanx of the third finger of his left hand. The patient did not have a costovertebral anomaly and his height was within normal limits. His initial EEG showed epileptiform activity in the frontocentral areas during sleep. His most recent EEG (after treatment with 2 antiepileptic drugs) showed absence seizures triggered by hyperventilation and photic stimulation. The authors proposed that the major clinical findings of KBG syndrome should be revised since most patients did not have costovertebral anomalies or short stature.
Gnazzo et al. (2020) reported 31 patients (18 females and 13 males) with heterozygous pathogenic variants of the ANKRD11 gene (28 patients) or 16q24 deletion encompassing the ANKRD11 gene (3 patients) seen at a single hospital in Italy. All mutations affected the C-terminal region at exon 9 of ANKRD11, including 17 frameshift and 11 nonsense mutations. Testing was done on both parents in 18 patients; 16 ANKRD11 variants were found to be de novo and 2 were inherited from affected mothers.
In the family from central Anatolia reported by Tekin et al. (2004), a father and 2 sons had KBG syndrome, confirming autosomal dominant inheritance.
Maegawa et al. (2004) reported a mildly affected mother and her severely affected son. Citing previous reports in which males were more severely affected than females (e.g., Parloir et al., 1977), they suggested that inheritance may be X-linked in some cases.
In the Turkish family with KBG syndrome originally reported by Tekin et al. (2004), Sirmaci et al. (2011) performed whole-exome capture followed by next-generation sequencing and identified a heterozygous splice site mutation in the ANKRD11 gene (611192.0001) that segregated with disease and was not found in ethnically matched controls. Analysis of ANKRD11 in 9 additional KBG probands, including 3 previously reported by Brancati et al. (2004), revealed heterozygosity for truncating mutations in 4 of them (see, e.g., 611192.0002 and 611192.0003). Sirmaci et al. (2011) noted that although the absence of ANKRD11 mutations in half of the families they studied suggested that KBG syndrome is genetically heterogeneous, variation in the regulatory regions of the gene could not be excluded.
Ansari et al. (2014) identified 2 different de novo heterozygous truncating mutations in the ANKRD11 gene (see, e.g., 611192.0004) in 2 unrelated patients with KBG syndrome. A third unrelated patient had an intragenic deletion in the ANKRD11 gene. The patients were ascertained from a larger cohort of patients with features consistent with Cornelia de Lange syndrome (see, e.g., CDLS1, 122470), thus showing phenotypic overlap between the 2 disorders. All had normal head circumference; detailed clinical features were not provided.
By exome sequencing in a boy with features of KBG syndrome, Geckinli et al. (2022) identified a de novo heterozygous missense mutation in the ANKRD11 gene (R1475S; 611192.0005). This variant was not found in large public databases including ExAC, gnomAD, and 1000 Genomes Project. The variant was not present in the proband's unaffected, first-cousin parents or in his sister, who had seizures but no other findings of KBG syndrome. The authors stated that the variant was classified as a variant of unknown significance by ACMG criteria.
Ansari, M., Poke, G., Ferry, Q., Williamson, K., Aldridge, R., Meynert, A. M., Bengani, H., Chan, C. Y., Kayserili, H., Avci, S., Hennekam, R. C. M., Lampe, A. K., and 63 others. Genetic heterogeneity in Cornelia de Lange syndrome (CdLS) and CdLS-like phenotypes with observed and predicted levels of mosaicism. J. Med. Genet. 51: 659-668, 2014. [PubMed: 25125236] [Full Text: https://doi.org/10.1136/jmedgenet-2014-102573]
Brancati, F., D'Avanzo, M. G., Digilio, M. C., Sarkozy, A., Biondi, M., De Brasi, D., Mingarelli, R., Dallapiccola, B. KBG syndrome in a cohort of Italian patients. Am. J. Med. Genet. 131A: 144-149, 2004. [PubMed: 15523620] [Full Text: https://doi.org/10.1002/ajmg.a.30292]
Devriendt, K., Holvoet, M., Fryns, J. P. Further delineation of the KBG syndrome. Genet. Counsel. 9: 191-194, 1998. [PubMed: 9777340]
Digilio, M. C., Calcagni, G., Gnazzo, M., Versacci, P., Dentici, M. L., Capolino, R., Sinibaldi, L., Baban, A., Putotto, C., Alfieri, P., Unolt, M., Lepri, F. R., Alesi, V., Genovese, S., Novelli, A., Marino, B., Dallapiccola, B. Congenital heart defects in molecularly confirmed KBG syndrome patients. Am. J. Med. Genet. 188A: 1149-1159, 2022. [PubMed: 34971082] [Full Text: https://doi.org/10.1002/ajmg.a.62632]
Fryns, J. P., Haspeslagh, M. Mental retardation, short stature, minor skeletal anomalies, craniofacial dysmorphism and macrodontia in two sisters and their mother: another variant example of the KBG syndrome? Clin. Genet. 26: 69-72, 1984. [PubMed: 6467660] [Full Text: https://doi.org/10.1111/j.1399-0004.1984.tb00792.x]
Geckinli, B. B., Alavanda, C., Arslan Ates, E., Yildirim, O., Arman, A. Enostosis in a patient with KBG syndrome caused by a novel missense ANKRD11 variant. Clin. Dysmorph. 31: 153-156, 2022. [PubMed: 35394473] [Full Text: https://doi.org/10.1097/MCD.0000000000000421]
Gnazzo, M., Lepri, F. R., Dentici, M. L., Capolino, R., Pisaneschi, E., Agolini, E., Rinelli, M., Alesi, V., Versacci, P., Genovese, S., Cesario, C., Sinibaldi, L., Baban, A., Bartuli, A., Marino, B., Cappa, M., Dallapiccola, B., Novelli, A., Digilio, M. C. KBG syndrome: Common and uncommon clinical features based on 31 new patients. Am. J. Med. Genet. 182A: 1073-1083, 2020. [PubMed: 32124548] [Full Text: https://doi.org/10.1002/ajmg.a.61524]
Herrmann, J., Pallister, P. D., Tiddy, W., Opitz, J. M. The KBG syndrome--a syndrome of short stature, characteristic facies, mental retardation, macrodontia and skeletal anomalies. Birth Defects Orig. Art. Ser. XI(5): 7-18, 1975. [PubMed: 1218237]
Maegawa, G. H. B., Leite, J. C. L., Felix, T. M., da Silveira, H. L. D., da Silveira, H. E. Clinical variability in KBG syndrome: report of three unrelated families. Am. J. Med. Genet. 131A: 150-154, 2004. [PubMed: 15384099] [Full Text: https://doi.org/10.1002/ajmg.a.30293]
Parloir, C., Fryns, J. P., Deroover, J., Lebas, E., Goffaux, P., van den Berghe, H. Short stature, craniofacial dysmorphism and dento-skeletal abnormalities in a large kindred: a variant of KBG syndrome or a new mental retardation syndrome. Clin. Genet. 12: 263-266, 1977. [PubMed: 589847] [Full Text: https://doi.org/10.1111/j.1399-0004.1977.tb00939.x]
Sirmaci, A., Spiliopoulos, M., Brancati, F., Powell, E., Duman, D., Abrams, A., Bademci, G., Agolini, E., Guo, S., Konuk, B., Kavaz, A., Blanton, S., Digilio, M. C., Dallapiccola, B., Young, J., Zuchner, S., Tekin, M. Mutations in ANKRD11 cause KBG syndrome, characterized by intellectual disability, skeletal malformations, and macrodontia. Am. J. Hum. Genet. 89: 289-294, 2011. [PubMed: 21782149] [Full Text: https://doi.org/10.1016/j.ajhg.2011.06.007]
Skjei, K. L., Martin, M. M., Slavotinek, A. M. KBG syndrome: report of twins, neurological characteristics, and delineation of diagnostic criteria. Am. J. Med. Genet. 143A: 292-300, 2007. [PubMed: 17230487] [Full Text: https://doi.org/10.1002/ajmg.a.31597]
Smithson, S. F., Thompson, E. M., McKinnon, A. G., Smith, I. S., Winter, R. M. The KBG syndrome. Clin. Dysmorph. 9: 87-91, 2000. [PubMed: 10826617] [Full Text: https://doi.org/10.1097/00019605-200009020-00002]
Soekarman, D., Volcke, P., Fryns, J.-P. The KBG syndrome: follow-up data on three affected brothers. Clin. Genet. 46: 283-286, 1994. [PubMed: 7834892] [Full Text: https://doi.org/10.1111/j.1399-0004.1994.tb04160.x]
Tekin, M., Kavaz, A., Berberoglu, M., Fitoz, S., Ekim, M., Ocal, G., Akar, N. The KBG syndrome: confirmation of autosomal dominant inheritance and further delineation of the phenotype. Am. J. Med. Genet. 130A: 284-287, 2004. [PubMed: 15378538] [Full Text: https://doi.org/10.1002/ajmg.a.30291]
Zollino, M., Battaglia, A., D'Avanzo, M. G., Della Bruna, M. M., Marini, G., Scarano, G., Cappa, M. Six additional cases of the KBG syndrome: clinical reports and outline of the diagnostic criteria. Am. J. Med. Genet. 52: 302-307, 1994. [PubMed: 7810561] [Full Text: https://doi.org/10.1002/ajmg.1320520310]