Identification of a PTEN mutation with reduced protein stability, phosphatase activity, and nuclear localization in Hong Kong patients with autistic features, neurodevelopmental delays, and macrocephaly

Abstract

PTEN is a tumor suppressor gene inactivated in over 30% of human cancers. It encodes a lipid phosphatase that serves as a gatekeeper of the phosphoinositide 3‐kinase signaling pathway. Germline mutation frequently occurs in this gene in patients diagnosed with PTEN Hamartoma Tumor Syndrome (PHTS). PHTS individuals are characterized by macrocephaly, benign growth of multiple tissues and increased tumor risk. In addition, autistic phenotypes are found in 10–20% of individuals carrying the germline PTEN mutation with macrocephaly. In this report, 13 suspected PHTS patients were screened for mutation in the PTEN gene. A missense variant (c. 302T > C) substituting the isoleucine at codon 101 to a threonine, a single nucleotide insertion (c. 327‐328insC) causing a frame shift mutation and termination at codon 109, and a nonsense variant (c. 1003C > T) truncated the protein at codon 335 were identified. The I101T mutation significantly reduced PTEN protein expression levels by 2.5‐ to 4.0‐fold. Mechanistically, I101T reduced the protein half‐life of PTEN possibly due to enhanced polyubiquitination at Lysine 13. However, the I101T mutant retained almost 30% of the lipid phosphatase activity of the wild‐type protein. Finally, the I101T mutant has reduced phosphorylation at a PTEN auto‐dephosphorylation site at Threonine 366 and a lowered ratio of nuclear to cytosolic protein level. These partial losses of multiple PTEN biochemical functions may contribute to the tissue overgrowth and autistic features of this PHTS patient. Autism Res 2018, 11: 1098–1109. © 2018 The Authors Autism Research published by International Society for Autism Research and Wiley Periodicals, Inc.Lay SummaryThe genetics of autism spectrum disorders is highly complex with individual risk influenced by both genetic and environmental factors. Mutation in the human PTEN gene confers a high risk of developing autistic behavior. This report revealed that PTEN mutations occurred in 23% of a selected group of Hong Kong patients harboring autistic features with gross overgrowth symptoms. Detailed characterization of a PTEN mutation revealed reduced protein stability as one of the underlying mechanisms responsible for reduced PTEN activity.

Behavioural and psychological features of PTEN mutations: a systematic review of the literature and meta-analysis of the prevalence of autism spectrum disorder characteristics

“…Further information shows a range of professionals diagnosed ASD including developmental paediatricians, multidisciplinary evaluation, neurologists, psychiatrics or other physicians. ADOS used for confirmation for 13 participants ASD ( n = 5), developmental delay without ASD ( n = 6) and expressive speech delay ( n = 1) 0.67 *Wong et al (2018), Hong Kong [ 59 ] Patients with suspected PHTS (indicated by autistic features and/or neurodevelopmental delays and macrocephaly) were referred for assessment and genetic testing to the Clinical Genetic Service (CGS) of Department of Health between January 1995 and September 2016. Records were also retrieved 3 (13) 2 (M) 9–10 years Unknown “Autism” or “Autistic features” stated in clinical features (further details on how this was diagnosed is not available) Intellectual disability ( n = 1), Autistic features ( n = 3) and developmental delay ( n = 2) 0.67 Yeung et al (2017), Hong Kong [ 60 ] Patients recruited from January 2013 to December 2016 at the Duchess of Kent Children’s Hospital Child Assessment Center.…”

“…In group A, four papers (31%) utilised or reported neuropsychological testing or measures, with seven (54%) gathering their data through medical records or developmental review and two (15%) not stating how the characteristics were assessed. In group B, nine papers (75%) reported at least one neuropsychological measure, and three studies did not provide this information [ 55 , 57 , 59 ].…”

Distinguishing between PTEN clinical phenotypes through mutation analysis

“…Similarly, mutations in patients clinically presenting with ASD, developmental or speech delay or mental retardation were assigned the ‘ASD’ class. To further exhaust the search for PTEN mutations in ASD, mutations present in ASD-dedicated databases VariCarta [41] and SFARI [42] were similarly compared with the literature [11] , [43] , [44] , [45] , [46] , [47] , [48] , [49] , [50] , [51] , [52] , [53] , [54] , [55] , [56] , [57] , [58] and assigned the ‘ASD’ phenotype. Notably, during machine learning, a subset of ASD mutations which were only identified in ASD cases, without PHTS symptoms, were kept as a clinical validation test set.…”

Autism‐associated PTEN missense mutation leads to enhanced nuclear localization and neurite outgrowth in an induced pluripotent stem cell line

“…An immunoprecipitation‐based lipid phosphatase assay was conducted as previously described [39]. Around 3 × 10 5 293T cells in 100‐mm plates were transfected by lipofection using 10 μg of various PTEN expression constructs.…”