Cascade Screening for Fragile X Syndrome/CGG Repeat Expansions in Children Attending Special Education in Sri Lanka

Abstract

Fragile X syndrome (FXS) is the commonest cause of inherited mental retardation and clinically presents with learning, emotional and behaviour problems. FXS is caused by expansion of cytosine-guanine-guanine (CGG) repeats present in the 5’ untranslated region of the FMR1 gene. The aim of this study was to screen children attending special education institutions in Sri Lanka to estimate the prevalence of CGG repeat expansions. The study population comprised a representative national sample of 850 children (540 males, 310 females) with 5 to 18 years of age from moderate to severe mental retardation of wide ranging aetiology. Screening for CGG repeat expansion was carried out on DNA extracted from buccal cells using 3’ direct triplet primed PCR followed by melting curve analysis. To identify the expanded status of screened positive samples, capillary electrophoresis, methylation specific PCR and Southern hybridization were carried out using venous blood samples. Prevalence of CGG repeat expansions was 2.2%. Further classification of the positive samples into FXS full mutation, pre-mutation and grey zone gave prevalence of 1.3%, 0.8% and 0.1% respectively. All positive cases were male. No females with FXS were detected in our study may have been due to the small sample size.

Molecular Correlates and Recent Advancements in the Diagnosis and Screening of FMR1-Related Disorders

“…Both assays are recommended to be performed as deletion at either end of a CGG-repeat expansion—reported in <1% of FXS cases—can prevent annealing of the FMR1 locus-specific primer, and result in drop-out of the expanded allele and failure to detect a true positive, if either one of these assays was applied alone [152]. While both 5′ and 3′ assays are efficient in identifying the presence of an expansion, the 3′ assay was found to be more robust in generating distinct melt profiles for NL, IM and expanded samples [152,153], and has been applied as a first-tier screen to assess the prevalence rates of IM, PM and FM among the children attending special education institutions in Sri Lanka [154]. Genomic DNA isolated from buccal swabs were used for preliminary screening, and all identified “expansion positives” were correctly verified by confirmatory molecular diagnostic tests.…”

Revisiting traditional SSR based methodologies available for elephant genetic studies

“…DNA from the fibres collected from the dung bolus was also extracted using the same kit. Human DNA was extracted using the method described by 107 and dissolved in TE buffer (Sigma, Cat no: 93283).…”

Inequities in diagnosis of Fragile X syndrome in Colombia

“…For instance, in a population‐based study conducted in the United States that included samples from 6,747 adults, the premutation prevalence was 1:468 males and 1:151 females (Seltzer et al, 2012). Prevalence studies have been carried out in newborns (Lévesque et al, 2009; Tassone et al, 2012), in individuals with intellectual disability (Alliende et al, 2008; Chandrasekara et al, 2015; Puusepp et al, 2008), pregnant woman or woman of reproductive age (Cheng et al, 2017; Ma et al, 2019) and in the general population. Hunter et al (2014) conducted the largest meta‐analysis study assessing prevalence estimates of the FM and PM in the general population.…”