Repeat expansion and methylation-sensitive triplet-primed polymerase chain reaction for fragile X mental retardation 1 gene screening in institutionalised intellectually disabled individuals

Abstract Fragile X syndrome is the most common cause of inherited mental retardation among males. In most cases, the molecular basis of fragile X syndrome is the expansion and subsequent methylation of a CGG trinucleotide repeat in the 5′ untranslated region of the fragile X mental retardation 1 (FMR1) gene. Laboratory diagnosis usually relies on a combination of Southern blot and polymerase chain reaction analyses. In this case report we describe an unusual Southern blot result in a patient who presented with developmental delay and had a normal CGG repeat number by polymerase chain reaction analysis. Further investigation revealed a novel G3310C transversion in the FMR1 gene resulting in a new recognition site for the BssHII restriction enzyme. This novel restriction site could potentially mimic a partial deletion of the FMR1 gene on Southern blot analysis and thus represents a possible pitfall in the diagnosis of fragile X syndrome.

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FMRP Levels in Human Peripheral Blood Leukocytes Correlates with Intellectual Disability

Diagnostics ◽

10.3390/diagnostics11101780 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1780

Author(s):

Mark Roth ◽

Lucienne Ronco ◽

Diego Cadavid ◽

Blythe Durbin-Johnson ◽

Randi J. Hagerman ◽

...

Keyword(s):

Mental Retardation ◽

Intellectual Disability ◽

Peripheral Blood ◽

Fragile X ◽

Repeat Expansion ◽

Repeat Number ◽

Cgg Repeat ◽

Fragile X Mental Retardation ◽

Cgg Repeats ◽

Fmr1 Mrna

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. FXS is an X-linked, neurodevelopmental disorder caused by a CGG trinucleotide repeat expansion in the 5′ untranslated region (UTR) of the Fragile X Mental Retardation gene, FMR1. Greater than 200 CGG repeats results in epigenetic silencing of the gene leading to the deficiency or absence of Fragile X mental retardation protein (FMRP). The loss of FMRP is considered the root cause of FXS. The relationship between neurological function and FMRP expression in peripheral blood mononuclear cells (PBMCs) has not been well established. Assays to detect and measure FMR1 and FMRP have been described; however, none are sufficiently sensitive, precise, or quantitative to properly characterize the relationships between cognitive ability and CGG repeat number, FMR1 mRNA expression, or FMRP expression measured in PBMCs. To address these limitations, two novel immunoassays were developed and optimized, an electro-chemiluminescence immunoassay and a multiparameter flow cytometry assay. Both assays were performed on PMBCs isolated from 27 study participants with FMR1 CGG repeats ranging from normal to full mutation. After correcting for methylation, a significant positive correlation between CGG repeat number and FMR1 mRNA expression levels and a significant negative correlation between FMRP levels and CGG repeat expansion was observed. Importantly, a high positive correlation was observed between intellectual quotient (IQ) and FMRP expression measured in PBMCs.

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5′ UTR CGG repeat expansion in GIPC1 is associated with oculopharyngodistal myopathy

Brain ◽

10.1093/brain/awaa426 ◽

2020 ◽

Author(s):

Jianying Xi ◽

Xilu Wang ◽

Dongyue Yue ◽

Tonghai Dou ◽

Qunfeng Wu ◽

...

Keyword(s):

Polymerase Chain Reaction ◽

Trinucleotide Repeat ◽

Late Onset ◽

Age At Onset ◽

Large Family ◽

Repeat Expansion ◽

Chain Reaction ◽

Cgg Repeat ◽

Sporadic Cases ◽

Polymerase Chain

Abstract Oculopharyngodistal myopathy is a late-onset degenerative muscle disorder characterized by ptosis and weakness of the facial, pharyngeal, and distal limb muscles. A recent report suggested a non-coding trinucleotide repeat expansion in LRP12 to be associated with the disease. Here we report a genetic study in a Chinese cohort of 41 patients with the clinical diagnosis of oculopharyngodistal myopathy (21 cases from seven families and 20 sporadic cases). In a large family with 12 affected individuals, combined haplotype and linkage analysis revealed a maximum two-point logarithm of the odds (LOD) score of 3.3 in chromosomal region chr19p13.11-p13.2 and narrowed the candidate region to an interval of 4.5 Mb. Using a comprehensive strategy combining whole-exome sequencing, long-read sequencing, repeat-primed polymerase chain reaction and GC-rich polymerase chain reaction, we identified an abnormal CGG repeat expansion in the 5′ UTR of the GIPC1 gene that co-segregated with disease. Overall, the repeat expansion in GIPC1 was identified in 51.9% independent pedigrees (4/7 families and 10/20 sporadic cases), while the repeat expansion in LRP12 was only identified in one sporadic case (3.7%) in our cohort. The number of CGG repeats was <30 in controls but >60 in affected individuals. There was a slight correlation between repeat size and the age at onset. Both repeat expansion and retraction were observed during transmission but somatic instability was not evident. These results further support that non-coding CGG repeat expansion plays an essential role in the pathogenesis of oculopharyngodistal myopathy.

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