Fragile X syndrome in Korea: a case series and a review of the literature

K. T, Justin Margret J, Venkataraman V, Natarajan Padmavathy K, Srisailapathy CRS. FMR1 gene CGG repeat distribution among the three individual cohorts with intellectual disability, autism, and primary ovarian insufficiency from Tamil Nadu, Southern India

Fragile X syndrome is the most common genetic cause of intellectual disability (ID) and is also well known to have a role in primary ovarian insufficiency (POI) and fragile X-associated tremor ataxia syndrome (FXTAS) that expresses across generations. The objective was to compare the CGG repeat variants in FMR1 gene among three correlating cohorts of ID, autism and idiopathic POI. Thirty-six patients with ID, 12 with autism spectrum disorder (ASD) and 13 females with idiopathic POI were screened for FMR1 CGG repeat size by fluorescent methylation-specific PCR and GeneScan analysis, irrespective of Hagerman checklist clinical scores. Among 29 males and seven females, 11 FMR1 allelic variants ranging from 21 to >200 CGG repeats were observed. Three (CF2-3, 39-5, 44-2) out of 29 males had full mutation alleles accounting for a 10.34% incidence of FXS among idiopathic ID males. One of them was a mosaic for CGG repeats with both premutation and full mutation alleles. The frequency of fragile X syndrome is high among patients with idiopathic ID; they also had a high score for the clinical check list. A cascade testing that begins with checklist evaluation prior to DNA analysis will be cost-effective for establishing early diagnosis in South India. With the huge disease burden, there is a need for the establishment of more molecular diagnostics and self-help groups for fragile X syndrome.

Lived Experiences of Fragile X Syndrome Caregivers: A Scoping Review of Qualitative Studies

Fragile X Syndrome (FXS) is the most common x-linked monogenic cause of Intellectual Disability (ID) and Autism Spectrum Disorder (ASD). Taking care of children with ID is challenging and overwhelming due to the multiple facets of caregiving. This scoping review aimed at summarizing the qualitative literature on the experiences of families living with FXS, identify key themes and determine the gaps in the extant literature. We conducted a literature search in May 2019 using four databases; PubMed, Web of Science, African-Wide-Information, and Scopus. The keywords used in our search strategy were associated with caregivers, lived experiences, FXS, and qualitative research. All English language articles with full-text reporting were included. Studies associated with other neurodevelopmental conditions and quantitative studies were excluded. We identified 12 out of 203 articles that described the lived experiences of families with FXS. Most articles originated from the United States of America and mothers were the main caregivers. We summarized our findings into four major themes which are; grief experiences, challenges of living with FXS, coping mechanisms and the need to plan for future outcomes. This scoping review highlights the scarcity of qualitative FXS literature in the African population and frustrations endured by families with FXS due to the low knowledge of FXS by healthcare workers. More research is needed to evaluate the impact of living with FXS in males and fathers.

Fragile X molecular investigation and genetic counseling of intellectual disability/developmental delay patients in an Indian scenario

Background: Fragile X Syndrome (FXS), the most common cause of inherited intellectual disability (ID), is caused by a CGG repeat expansion (full mutation (FM), >200 CGG) at the Fragile X Mental Retardation 1 (FMR1) gene. Early identification of FXS has prognostic significance for affected individuals due to early initiation of interventions. Genetic counseling and family screening can aid parents and at-risk asymptomatic carriers (premutation (PM), 55-200 CGG) in taking proper reproductive decisions. Methodology: The present study utilizes Triplet Primed-Polymerase Chain Reaction (TP-PCR) methodology for detecting the repeat expansion at FMR1 gene in 233 Indian intellectual disability/developmental delay (ID/DD) patients. Results: We have identified 18/233 (7.7%) FXS positive cases. Early diagnosis was made in 66.7% cases (<10 years). Extended family screening in 14 affected individuals identified 9 additional FM cases (7 males and 2 females) and 23 carrier PM females, which otherwise could have been missed. Four prenatal diagnoses were also performed, leading to the identification of 1 PM and 1 FM carrier fetus. Conclusion: A high frequency (7.7%) of FXS among Indian ID/DD subjects obtained in this study depicted the need for more professional recommendations concerning prompt referral for genetic testing, and increased exposure to information about FXS to pediatricians.

Usefulness of fragile X checklist and CGG distribution in specialized institutions in Kinshasa, DR Congo

Screening for fragile X syndrome (FXS) is essential in children with developmental delay or intellectual disability (ID). In addition, using clinical screening checklists remains of high interest in resource-limited settings. We aimed to gain insight into the prevalence of FXS and the distribution of CGG alleles and to evaluate the usefulness of three checklists in specialized institutions in Kinshasa, DR Congo. We recruited 80 males and 25 females from six specialized institutions in Kinshasa and administered a questionnaire comprising items from the following FXS checklists: Hagerman, Maes, and Guruju. FMR1 CGG repeats were assessed for every patient. About 37% of patients were referable for FX testing based on Hagerman's checklist, 35% for Maes', and 43.80% for Guruju's, but none of them was molecularly confirmed to have FXS. Thus, specificities were 62.86, 64.76, and 56.5%, respectively, for Hagerman, Maes, and Guruju, respectively. The mean CGG allele size was 28.55 ± 2.83 (ranges, 17-48). The 29 CGG was the most frequent allele (24.61%). Thus, existing checklists should not be automatically applied to Congolese patients without adjustments. The distribution of CGG repeats and the number of CGG alleles are similar to other African studies.

Common Clinical Characteristics and Rare Medical Problems of Fragile X Syndrome in Thai Patients and Review of the Literature

Background. Clinical characteristics of fragile X syndrome (FXS) have been well documented in Caucasians, whereas in Asians they have rarely been described. Those that have been conducted used small cohorts that utilized DNA for diagnosis and larger cohorts that utilized cytogenetics for diagnosis. This study is to describe clinical characteristics of FXS in a large cohort of Thai patients diagnosed by standard molecular methods. Methods. Seventy-seven index cases and 46 affected relatives diagnosed with FXS were recruited into the study. To determine frequencies of common characteristics of FXS in prepubertal boys, we reviewed 56 unrelated cases aged between 18 and 146 months. To list rare medical problems, we reviewed 75 cases aged between 8 months to 71 years old, including 53 index cases and 22 affected relatives. In addition, we selected 16 clinical studies from various ethnicities for comparison with our findings. Results. In prepubertal boys with FXS, attention deficit and/or hyperactivity, prominent ears, macroorchidism, and elongated face were observed in 96%, 80%, 53%, and 48% of patients, respectively, whereas recognizable X-linked inheritance presented in 11% of patients. IQ scores ranged between 30 and 64 (mean ± SD = 43 ± 9, n = 25). We observed clinical findings that rarely or have never been reported, for example, medulloblastoma and tetralogy of Fallot. Conclusion. Attention deficit and/or hyperactivity and prominent ear are the most common behavioral and physical features in prepubertal boys with FXS, respectively. There are differences in frequencies of clinical characteristics observed between ethnicities; however, it is difficult to draw a solid conclusion due to different recruitment criteria and sample sizes within each study.

Parents' initial concerns about the development of their children later diagnosed with fragile X syndrome

BACKGROUND

Retrospective parental reports have often been used to identify the early characteristics of children later diagnosed with a developmental disorder.

METHOD

We applied this methodology to document 13 parents' initial concerns about the development of their 17 children later diagnosed with fragile X syndrome (FXS). Parents were additionally asked about when they noticed the emergence of behavioural signs related to FXS.

RESULTS

More than half of the parents reported initial concerns prior to the child's first birthday and in most cases it was deviant motor behaviours that caused the first concerns. Behavioural signs related to the FXS phenotype were also reported to be perceptible in the first year of the child's life.

CONCLUSIONS

Due to limitations of retrospective parental questionnaires, we suggest that other methodologies, such as home video analysis, are needed to complement our understanding of the pathways of developmental disorders with late clinical onsets.

Fragile X syndrome: panoramic radiographic evaluation of dental anomalies, dental mineralization stage, and mandibular angle

Fragile X syndrome (FXS) is a disorder linked to the chromosome X long arm (Xq27.3), which is identified by a constriction named fragile site. It determines various changes, such as behavioral or emotional problems, learning difficulties, and intellectual disabilities. Craniofacial abnormalities such as elongated and narrow face, prominent forehead, broad nose, large and prominent ear pavilions, strabismus, and myopia are frequent characteristics. Regarding the oral aspects, deep and high-arched palate, mandibular prognathism, and malocclusion are also observed.

Molecular diagnosis of Fragile X syndrome in subjects with intellectual disability of unknown origin: implications of its prevalence in regional Pakistan

Fragile-X syndrome (FXS) is the most common form of inherited intellectual disability (ID) and affects 0.7–3.0% of intellectually compromised population of unknown etiology worldwide. It is mostly caused by repeat expansion mutations in the FMR1 at chromosome Xq27.3. The present study aimed to develop molecular diagnostic tools for a better detection of FXS, to assess implementation of diagnostic protocols in a developing country and to estimate the prevalence of FXS in a cohort of intellectually disabled subjects from Pakistan. From a large pool of individuals with below normal IQ range, 395 subjects with intellectual disability of unknown etiology belonging to different regions of the country were recruited. Conventional-PCR, modified-PCR and Southern blot analysis methods were employed for the detection of CGG repeat polymorphisms in the FMR1 gene. Initial screening with conventional-PCR identified 13 suspected patients. Subsequent investigations through modified PCR and Southern blot analyses confirmed the presence of the FMR1 mutation, suggesting a prevalence of 3.5% and 2.8% (mean 3.3%) among the male and female ID patients, respectively. These diagnostic methods were further customized with the in-house conditions to offer robust screening of referral patients/families for diagnostics and genetic counseling. Prescreening and early diagnosis are crucial for designing a prudent strategy for the management of subjects with ID. Outcome of the study recommends health practitioners for implementation of molecular based FXS diagnosis in routine clinical practice to give a better care for patients similar to the ones included in the study.

Frequency of FMR1 gene mutation and CGG repeat polymorphism in intellectually disabled children in Pakistan

Fragile X syndrome is considered the most common heritable form of X-linked intellectual disability (ID). The syndrome is caused by silencing of the fragile X mental retardation 1 gene (Xq27.3) due to hypermethylation. This mutation results in absence or deficit of its protein product, the fragile X mental retardation protein (FMRP) that affects synaptic plasticity in neurons, hence leads to brain dysfunction. The syndrome is widely distributed throughout the world. This study reported for the first time the frequency of the fragile X mental retardation 1 gene mutations in intellectually disabled children in Pakistan. We recruited 333 intellectually disabled children and 250 normal children with age ranging from 5 to 18 years for this study. Genomic DNA was extracted from peripheral blood and full mutations were identified by methylation sensitive PCR using primers corresponding to modified methylated and unmethylated DNA. Southern blot was used for confirmation of the results. The frequency of fragile X syndrome with full mutation was found as 4.8%. It was 6.5% in males as opposed to 0.9% in females; 29 CGG repeats were found as the most common allele; 31.5% in the intellectually disabled and 34% in control subjects. In Pakistan intellectual disability is considered as a social stigma for the individuals and their families. Due to lack of knowledge and cultural background people make such patients and families isolated. This study will increase public awareness about the intellectual disability and importance of prenatal screening and genetic counseling for vulnerable families.

Fragile X carrier screening in Korean women of reproductive age

OBJECTIVE

To estimate the distribution of the FMR1 alleles and the prevalence of the premutaion (PM) and full mutation (FM) of the FMR1 gene in Korean women of reproductive age.

METHODS

Using polymerase chain reaction and Southern blot, 5829 women of reproductive age were screened (low-risk group n = 5470 and high-risk group n = 359) and 11 prenatal diagnoses were completed between September 2003 and December 2011.

RESULTS

Of the 5829 women screened, normal FMR1 alleles (11,607) had a bimodal distribution with most alleles having 29 (37.87%) and 30 (31.87%) CGG repeats. Of the 5470 women in the low-risk group, 7 PM were identified, giving a PM carrier frequency of 1:781; none of the women had Fragile X syndrome. We also identified 38 intermediate alleles, with a reported incidence of 1:143. Of the 11 prenatal diagnoses, five were normal, five had a premutation, and one had a full mutation allele.

CONCLUSIONS

The carrier frequency is 1/781 (0.13%) in Korean women of reproductive age. This is lower than among Caucasians, but relatively higher than in other Asian populations. Although there may be a founder effect, these results might be valuable in understanding Fragile X syndrome in Koreans and Asians as a whole.

Fragile X syndrome: the FMR1 CGG repeat distribution among world populations

Fragile X syndrome (FXS) is characterized by moderate to severe intellectual disability, which is accompanied by macroorchidism and distinct facial morphology. FXS is caused by the expansion of the CGG trinucleotide repeat in the 5' untranslated region of the fragile X mental retardation 1 (FMR1) gene. The syndrome has been studied in ethnically diverse populations around the world and has been extensively characterized in several populations. Similar to other trinucleotide expansion disorders, the gene-specific instability of FMR1 is not accompanied by genomic instability. Currently we do not have a comprehensive understanding of the molecular underpinnings of gene-specific instability associated with tandem repeats. Molecular evidence from in vitro experiments and animal models supports several pathways for gene-specific trinucleotide repeat expansion. However, whether the mechanisms reported from other systems contribute to trinucleotide repeat expansion in humans is not clear. To understand how repeat instability in humans could occur, the CGG repeat expansion is explored through molecular analysis and population studies which characterized CGG repeat alleles of FMR1. Finally, the review discusses the relevance of these studies in understanding the mechanism of trinucleotide repeat expansion in FXS.