RESUMO
PURPOSE: Postzygotic (somatic) variants in the mTOR pathway genes cause a spectrum of distinct developmental abnormalities. Accurate classification of somatic variants in this group of disorders is crucial for affected individuals and their families. METHODS: The ClinGen Brain Malformation Variant Curation Expert Panel was formed to curate somatic variants associated with developmental brain malformations. We selected the genes AKT3, MTOR, PIK3CA, and PIK3R2 as the first set of genes to provide additional specifications to the 2015 American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) sequence variant interpretation guidelines, which currently focus solely on germline variants. RESULTS: A total of 24 of the original 28 ACMG/AMP criteria required modification. Several modifications used could be applied to other genes and disorders in which somatic variants play a role: 1) using variant allele fraction differences as evidence that somatic mutagenesis occurred as a proxy for de novo variation, 2) incorporating both somatic and germline evidence, and 3) delineating phenotype on the basis of variable tissue expression. CONCLUSION: We have established a framework for rigorous interpretation of somatic mosaic variants, addressing issues unique to somatic variants that will be applicable to many genes and conditions.
Assuntos
Encéfalo , Anormalidades Congênitas , Variação Genética , Genoma Humano , Humanos , Encéfalo/patologia , Classe I de Fosfatidilinositol 3-Quinases/genética , Anormalidades Congênitas/genética , Testes Genéticos , Variação Genética/genética , Mutação , Fosfatidilinositol 3-Quinases , Proteínas Proto-Oncogênicas c-akt/genética , Serina-Treonina Quinases TOR/genéticaRESUMO
BACKGROUND AND PURPOSE: Intracranial manifestations of Langerhans cell histiocytosis (LCH) are underestimated in frequency and diversity. We categorized the spectrum of MR imaging changes in LCH. METHODS: We retrospectively reviewed 474 MR images in 163 patients with LCH and 55 control subjects. Lesions were characterized by anatomic region and signal intensity. Brain atrophy was assessed. RESULTS: We noted osseous lesions in the craniofacial or skull bones in 56% of patients, meningeal lesions in 29%, and choroid-plexus involvement in 6%. In the hypothalamic-pituitary region, infundibular thickening occurred in 50%; pronounced hypothalamic mass lesions in 10%; and infundibular atrophy in 29%. The pineal gland had a cystic appearance in 28%, and pineal-gland enlargement (>10 mm) was noted in 14%. Nonspecific paranasal-sinus or mastoid opacifications were seen in 55% of patients versus 20% of controls, and accentuated Virchow-Robin spaces occurred in 70% of patients versus 27% of controls (P <.001). Intra-axial, white-matter parenchymal changes resulted in a leukoencephalopathy-like pattern in 36%. Enhancing lesions in a vascular distribution were noted in 5%. Gray-matter changes suggestive of neurodegeneration were identified in the cerebellar dentate nucleus in 40% and in the supratentorial basal ganglia in 26%. All patients with neurodegenerative lesions had lesions in the extra-axial spaces. Cerebral atrophy was found in 8%. CONCLUSION: In LCH, cranial and intracranial changes at MR imaging include 1) lesions of the craniofacial bone and skull base with or without soft-tissue extension; 2) intracranial, extra-axial changes (hypothalamic-pituitary region, meninges, circumventricular organs); 3) intracranial, intra-axial changes (white matter and gray matter); and 4) cerebral atrophy.