title: Determining the pathogenicity of patient-derived TSC2 mutations by functional characterization and clinical evidence.
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.
authors.affiliation: Institute of Medical Genetics, Cardiff University, Heath Park, Cardiff, UK.
authors.forename: Elaine A
authors.initials: EA
authors.lastname: Dunlop
authors.forename: Kayleigh M
authors.initials: KM
authors.lastname: Dodd
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Land
authors.forename: Peter A
authors.initials: PA
authors.lastname: Davies
authors.forename: Nicole
authors.initials: N
authors.lastname: Martins
authors.forename: Helen
authors.initials: H
authors.lastname: Stuart
authors.forename: Shane
authors.initials: S
authors.lastname: McKee
authors.forename: Chris
authors.initials: C
authors.lastname: Kingswood
authors.forename: Anand
authors.initials: A
authors.lastname: Saggar
authors.forename: Isabel
authors.initials: I
authors.lastname: Corderio
authors.forename: Ana Maria Duarte
authors.initials: AM
authors.lastname: Medeira
authors.forename: Helen
authors.initials: H
authors.lastname: Kingston
authors.forename: Julian R
authors.initials: JR
authors.lastname: Sampson
authors.forename: David Mark
authors.initials: DM
authors.lastname: Davies
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Tee
mesh_terms: D000293:Adolescent; D000818:Animals; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D030342:Genetic Diseases, Inborn / Q000235:genetics / Q000503:physiopathology; D005838:Genotype; D057809:HEK293 Cells; D006801:Humans; D007223:Infant; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D010766:Phosphorylation / Q000235:genetics; D055503:Protein Multimerization / Q000235:genetics; D055550:Protein Stability; D011506:Proteins / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D046912:Multiprotein Complexes; D011506:Proteins; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; C000624651:Tsc1 protein, mouse; C000624654:Tsc2 protein, mouse; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases