A combination of genetic and biochemical analyses for the diagnosis of PI3K-AKT-mTOR pathway-associated megalencephalyReport as inadecuate




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BMC Medical Genetics

, 18:4

Clinical-Molecular Genetics and Cytogenetics

Abstract

BackgroundConstitutive activation of the PI3K-AKT-mTOR pathway mTOR pathway underlies megalencephaly in many patients. Yet, prevalence of the involvement of the PI3K-AKT-mTOR pathway in patients with megalencephaly remains to be elucidated, and molecular diagnosis is challenging. Here, we have successfully established a combination of genetic and biochemical methods for diagnosis of mTOR pathway-associated megalencephaly, and have attempted to delineate the clinical characteristics of the disorder.

MethodsThirteen patients with an increased head circumference and neurological symptoms participated in the study. To evaluate the activation of the mTOR pathway, we performed western blot analysis to determine the expression levels of phosphorylated S6 ribosomal protein phospho-S6 protein in lymphoblastoid cell lines from 12 patients. Multiplex targeted sequencing analysis for 15 genes involved in the mTOR pathway was performed on 12 patients, and whole-exome sequencing was performed on one additional patient. Clinical features and MRI findings were also investigated.

ResultsWe identified pathogenic mutations in six AKT3, 1 patient; PIK3R2, 2 patients; PTEN, 3 patients of the 13 patients. Increased expression of phospho-S6 protein was demonstrated in all five mutation-positive patients in whom western blotting was performed, as well as in three mutation-negative patients. Developmental delay, dysmorphic facial features were observed in almost all patients. Syndactyly-polydactyly and capillary malformations were not observed, even in patients with AKT3 or PIK3R2 mutations. There were no common phenotypes or MRI findings among these patients.

ConclusionsA combination of genetic and biochemical methods successfully identified mTOR pathway involvement in nine of 13 approximately 70% patients with megalencephaly, indicating a major contribution of the pathway to the pathogenesis of megalencephaly. Our combined approach could be useful to identify patients who are suitable for future clinical trials using an mTOR inhibitor.

KeywordsAKT3 MCAP MPPH Multiplex targeted sequencing Phosphorylated S6 ribosomal protein PIK3R2 PTEN AbbreviationsLCLLymphoblastoid cell line

MCAPMegalencephaly-capillary malformation syndrome

MPPHMegalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome

MRIMagnetic resonance imaging

mTORMechanistic target of rapamycin

SDStandard deviation

WESWhole exome sequencing

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Author: Yutaka Negishi - Fuyuki Miya - Ayako Hattori - Yoshikazu Johmura - Motoo Nakagawa - Naoki Ando - Ikumi Hori - Takao Togawa

Source: https://link.springer.com/



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