Identification of Expanded Alleles of theFMR1Gene Among High-Risk Population in Indonesia by Using Blood Spot Screening

Abstract

The prevalence of Fragile X Syndrome (FXS) is 1 in 4000 in males and 1 in 2500 in males and females, respectively, in the general population. Several screening studies aimed at determining the prevalence of FXS have been conducted in individuals with intellectual disabilities (IDs) with a prevalence varying from 1.15% to 6.3% across different ethnic groups. A previous study in Indonesia showed an FXS prevalence of 1.9% among the ID population. A rapid, effective, and inexpensive method for FMR1 screening, using dried blood spots capable of detecting an expanded FMR1 allele in both males and females, was recently reported. We used this approach to screen 176 blood spots, collected from Central Java, Indonesia, for the presence of expanded FMR1 gene alleles. Samples were collected from high-risk populations: 112 individuals with ID, 32 obtained from individuals with diagnosis of autism spectrum disorders, and 32 individuals with a known family history of FXS. Fourteen subjects carrying an FMR1 expanded allele were identified including 7 premutations (55-200 CGG repeats) and 7 full mutations ( > 200 repeats). Of the seven subjects identified with a full mutation, one subject was from a nonfragile X family, and six from were families with a history of FXS.Introduction F ragile X syndrome (FXS), with a prevalence of 1:2500 to 1:4000 in the general population (Turner et al., 1996;Crawford et al., 2002;Hagerman, 2008), is the most common genetic cause of intellectual disability (ID) and the leading genetic cause of autism. Although prevalence estimates vary across studies, there is agreement that the risk of autism spectrum disorders (ASD) is higher in FXS than in many other neuro-developmental disorders. From recent studies, *2% to 6% of children with ASD have FXS (Li et al., 1993;Wassink et al., 2001;Estecio et al., 2002;Hagerman, 2002;Reddy, 2005), and *30% of children with FXS have ASD (see Appendix in Rogers et al., 2001;Kaufmann et al., 2004); Pervasive Developmental Disorder-Not Otherwise Specified is seen in an additional 30% (Harris et al., 2008). In fact, FXS is characterized by a broad spectrum of behavioral and emotional impairment, psychological problems, and learning disabilities in those without mental retardation or ID. In addition, specific physical features such as long face, macrognathia, prominent ears, hyperextensible joints, flat feet, and macroorchidism in puberty are observed (Hagerman et al., 1991;Lachiewicz and Dawson, 1994;Giangreco et al., 1996). The milder phenotypes are not accounted for in the current prevalence figures (Tassone et al., 1999;Hagerman, 2006). In addition, significant phenotypic involvement has emerged in some individuals with the premutation (55-200 CGG repeats), including fragile X-associated premature ovarian insufficiency (FXPOI) in females, and fragile X-associated tremor/ataxia syndrome (FXTAS) in both male and female aging carriers Sullivan et al., 2005). Prevalence for premutation alleles was *1 in 110-250 for females and 1 in 250-800 for males (Rousseau et al., 199...

Distribution of AGG interruption patterns within nine world populations

“…A large portion of normal alleles with 3 AGG interruptions (8%), with the majority of these alleles having the 9-A-9-A-6-A-9 pattern (6.4% of patterns) was observed in Indonesia. The 9-A-9-A-6-A-9 pattern and CGG length of 36 repeats has been observed in previous studies to occur within Indonesian and Asian cohorts (30,38,39). Fifty AGG interruption patterns were observed in 277 FMR1 alleles genotyped from Mexico.…”

“…These samples were previously screened to determine the prevalence rates of expanded alleles. Cohorts from Australia (n = 201) (28), Chile (n = 77), the United Arab Emirates (n = 263), Guatemala (n = 151) (29), Indonesia (n = 312) (30), Italy (n = 67), Mexico (n = 277), Spain (n = 358) (31), and the United States (n = 1,359) (32) were included. Individuals were recruited from the general population for the Italy, Spain, and United States samples.…”

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

“…(6,13) Another study conducted in 2012 by Winarni et al showed that the most common CGG repeat allele in an Indonesian high-risk population was 30 repeats, followed by 29 repeats, with a smaller percentage of 35 and 36 repeats. (11) Using sizing analysis, two out of five samples that were classified as expanded with respect to the 53-repeat reference control (TG-143 and TG-271) were determined to carry FM alleles of > 200 repeats, although the exact sizes of the FM expansions could not be determined by the kit. The remaining three samples that were classified as expanded (TG-153, TG-174 and TG-192) were false positives.…”

“…Screening for FXS in high-risk populations such as those with ID is an effective means of identifying affected individuals and determining the prevalence of ID, and allow family members to undergo posttest genetic counselling sessions and cascade testing. (11) This study utilised a simple, quick and inexpensive method with high sensitivity and specificity for diagnosing FXS among institutionalised individuals with ID. (12)…”

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

“…Study populations have varied widely according to diagnostic categories of the subjects included. For example, an Indonesian study found a prevalence of 6 in 32 where there was a family history of FXS, but 1 in 144 in those with intellectual impairment alone [ 42 ]. A reported low prevalence of 1.1% from United States among children attending special education schools also included mentally retarded (12%), autism spectrum disorder (1%), learning disability (51%) and attention deficit hyperactivity disorder (35%) [ 43 ].…”