Missense variants in ANKRD11 cause KBG syndrome by impairment of stability or transcriptional activity of the encoded protein.

PURPOSE: Although haploinsufficiency of ANKRD11 is among the most common genetic causes of neurodevelopmental disorders, the role of rare ANKRD11 missense variation remains unclear. We characterized clinical, molecular, and functional spectra of ANKRD11 missense variants. METHODS: We collected clinical information of individuals with ANKRD11 missense variants and evaluated phenotypic fit to KBG syndrome. We assessed pathogenicity of variants through in silico analyses and cell-based experiments. RESULTS: We identified 20 unique, mostly de novo, ANKRD11 missense variants in 29 individuals, presenting with syndromic neurodevelopmental disorders similar to KBG syndrome caused by ANKRD11 protein truncating variants or 16q24.3 microdeletions. Missense variants significantly clustered in repression domain 2 at the ANKRD11 C-terminus. Of the 10 functionally studied missense variants, 6 reduced ANKRD11 stability. One variant caused decreased proteasome degradation and loss of ANKRD11 transcriptional activity. CONCLUSION: Our study indicates that pathogenic heterozygous ANKRD11 missense variants cause the clinically recognizable KBG syndrome. Disrupted transrepression capacity and reduced protein stability each independently lead to ANKRD11 loss-of-function, consistent with haploinsufficiency. This highlights the diagnostic relevance of ANKRD11 missense variants, but also poses diagnostic challenges because the KBG-associated phenotype may be mild and inherited pathogenic ANKRD11 (missense) variants are increasingly observed, warranting stringent variant classification and careful phenotyping.

Kosaki overgrowth syndrome: A novel pathogenic variant in PDGFRB and expansion of the phenotype including cerebrovascular complications.

Heterozygous activating variants in platelet-derived growth factor, beta (PDGFRB) are associated with phenotypes including Kosaki overgrowth syndrome (KOGS), Penttinen syndrome and infantile myofibromatosis (IM). Here, we present three new cases of KOGS, including a patient with a novel de novo variant c.1477A > T p.(Ser493Cys), and the oldest known individual age 53 years. The KOGS phenotype includes characteristic facial features, tall stature, scoliosis, hyperelastic thin skin, lipodystrophy, variable intellectual and neurological deterioration, and abnormalities on brain imaging. Long-term outcome is unknown. Our cases confirm the phenotypic spectrum includes progressive flexion contractures, camptodactyly, widely spaced teeth, and constriction rings. We also propose novel occasional features including craniosynostosis, ocular pterygia, anterior chamber cleavage syndrome, early osteoporosis, increased pigmentation, recurrent haematomas, predisposition to cellulitis, nail dystrophy, carpal tunnel syndrome, recurrent hypoglycaemia in infancy, joint dislocation, and splenomegaly. Importantly, we report fusiform aneurysm of the basilar artery in two patients. Complications include thrombosis and stroke in the oldest reported patient and fatal rupture at the age of 21 in the patient with the novel variant. We conclude that cerebrovascular complications are part of the phenotypic spectrum of KOGS and KOGS-like disorders and suggest vascular imaging is indicated in these patients.

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

KBG syndrome, due to ANKRD11 alteration is characterized by developmental delay, short stature, dysmorphic facial features, and skeletal anomalies. We report a clinical and molecular study of 39 patients affected by KBG syndrome. Among them, 19 were diagnosed after the detection of a 16q24.3 deletion encompassing the ANKRD11 gene by array CGH. In the 20 remaining patients, the clinical suspicion was confirmed by the identification of an ANKRD11 mutation by direct sequencing. We present arguments to modulate the previously reported diagnostic criteria. Macrodontia should no longer be considered a mandatory feature. KBG syndrome is compatible with autonomous life in adulthood. Autism is less frequent than previously reported. We also describe new clinical findings with a potential impact on the follow-up of patients, such as precocious puberty and a case of malignancy. Most deletions remove the 5'end or the entire coding region but never extend toward 16q telomere suggesting that distal 16q deletion could be lethal. Although ANKRD11 appears to be a major gene associated with intellectual disability, KBG syndrome remains under-diagnosed. NGS-based approaches for sequencing will improve the detection of point mutations in this gene. Broad knowledge of the clinical phenotype is essential for a correct interpretation of the molecular results. © 2016 Wiley Periodicals, Inc.

Postzygotic inactivating mutations of RHOA cause a mosaic neuroectodermal syndrome.

Hypopigmentation along Blaschko's lines is a hallmark of a poorly defined group of mosaic syndromes whose genetic causes are unknown. Here we show that postzygotic inactivating mutations of RHOA cause a neuroectodermal syndrome combining linear hypopigmentation, alopecia, apparently asymptomatic leukoencephalopathy, and facial, ocular, dental and acral anomalies. Our findings pave the way toward elucidating the etiology of pigmentary mosaicism and highlight the role of RHOA in human development and disease.