Determining the pathogenicity of patient-derived TSC2 mutations by functional characterization and clinical evidence

Elaine A. Dunlop, Kayleigh M. Dodd, Stephen C. Land, Peter A. Davies, Nicole Martins, Helen Stuart, Shane McKee, Chris Kingswood, Anand Saggar, Isabel Corderio, Ana Maria Duarte Medeira, Helen Kingston, Julian R. Sampson, David Mark Davies, Andrew R. Tee

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    Abstract

    Tuberous sclerosis complex (TSC) is a genetic condition characterized by the growth of benign tumours in multiple organs, including the brain and kidneys, alongside intellectual disability and seizures. Identification of a causative mutation in TSC1 or TSC2 is important for accurate genetic counselling in affected families, but it is not always clear from genetic data whether a sequence variant is pathogenic or not. In vitro functional analysis could provide support for determining whether an unclassified TSC1 or TSC2 variant is disease-causing. We have performed a detailed functional analysis of four patient-derived TSC2 mutations, E92V, R505Q, H597R and L1624P. One mutant, E92V, functioned similarly to wild-type TSC2, whereas H597R and L1624P had abnormal function in all assays, consistent with available clinical and segregation information. One TSC2 mutation, R505Q, was identified in a patient with intellectual disability, seizures and autistic spectrum disorder but who did not fulfil the diagnostic criteria for TSC. The R505Q mutation was also found in two relatives, one with mild learning difficulties and one without apparent phenotypic abnormality. R505Q TSC2 exhibited partially disrupted function in our assays. These data highlight the difficulties of assessing pathogenicity of a mutation and suggest that multiple lines of evidence, both genetic and functional, are required to assess the pathogenicity of some mutations. European Journal of Human Genetics (2011) 19, 789-795; doi:10.1038/ejhg.2011.38; published online 16 March 2011

    Original languageEnglish
    Pages (from-to)789-795
    Number of pages7
    JournalEuropean Journal of Human Genetics
    Volume19
    Issue number7
    DOIs
    Publication statusPublished - 2011

    Keywords

    • TSC
    • mutation
    • function
    • pathogenicity
    • TUBEROUS SCLEROSIS COMPLEX
    • MISSENSE MUTATIONS
    • MAMMALIAN TARGET
    • GENE-PRODUCTS
    • IDENTIFICATION
    • MTOR
    • RHEB
    • MOTIF
    • PHOSPHORYLATION
    • GTPASE

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