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Mosaicism for a full mutation, premutation, and deletion of the CGG repeats results in 22% FMRP and elevated FMR1 mRNA levels in a high‐functioning fragile X male
Author(s) -
Han XiaoDong,
Powell Berkley R.,
Phalin Judith L.,
Chehab Farid F.
Publication year - 2006
Publication title -
american journal of medical genetics part a
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.064
H-Index - 112
eISSN - 1552-4833
pISSN - 1552-4825
DOI - 10.1002/ajmg.a.31291
Subject(s) - fmr1 , fragile x syndrome , genetics , fragile x , mutation , biology , psychology , gene
The molecular basis in the majority of fragile X patients results from expansion of the CGG repeats in the FMR1 gene causing its transcriptional silencing and deficiency of its encoded protein FMRP. In this communication, we report on a male patient who lacks the characteristic physical features of fragile X and carries a fully methylated mutation, a premutation, a non‐methylated full mutation, and a microdeletion encompassing the entire CGG repeat region and 42 bp of upstream flanking sequence. Southern blot analysis revealed that the methylated full mutation accounted for only 10% of his genotype while the premutation/non‐methylated full mutation and the microdeletion constituted 37% and 53%, respectively. Immunofluorescent staining of FMRP demonstrated the presence of 22% FMRP in his peripheral blood leukocytes and quantitative RT‐PCR revealed a 3.6‐fold elevation of FMR1 mRNA levels. Developmental assessments indicated that while he has a learning disability, he does not have mental retardation. Because previous reports had noted that 28% FMRP expression is associated with a characteristic fragile X phenotype, we propose that in our patient the association of 22% FMRP levels with normal physical features and a high‐functioning status may have resulted from increased FMRP stability by a mechanism that takes into account the CGG microdeletion and elevated mRNA levels. © 2006 Wiley‐Liss, Inc.