Cascade Testing for Fragile X Syndrome in a Rural Setting in Cameroon (Sub-Saharan Africa)

Fragile X Syndrome (FXS), an X-linked dominant monogenic condition, is the main genetic cause of intellectual disability (ID) and autism spectrum disorder (ASD). FXS is associated with an expansion of CGG repeat sequence in the Fragile X Mental Retardation gene 1 (FMR1) on chromosome X. Following a neuropediatric assessment of two male siblings who presented with signs of FXS that was confirmed with molecular testing, we provided cascade counselling and testing to the extended family. A total of 46 individuals were tested for FXS; among them, 58.70% (n = 27) were females. The mean age was 9.4 (±5) years for children and 45.9 (±15.9) years for adults. Pedigree analysis suggested that the founder of these families was likely a normal transmitting male. Four out of 19 males with clinical ID were confirmed to have a full mutation for FXS, while 14/27 females had a pathologic CGG expansion (>56 CGG repeats) on one of their X chromosomes. Two women with premature menopause were confirmed of being carriers of premutation (91 and 101 CGG repeats). We also identified maternal alleles (91 and 126 CGG repeats) which expanded to a full mutation in their offspring (>200 CGG repeats). This study is a rare report on FXS from Africa and illustrates the case scenario of implementing genetic medicine for a neurogenetic condition in a rural setting.

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A Novel FMR1 PCR Method for the Routine Detection of Low Abundance Expanded Alleles and Full Mutations in Fragile X Syndrome

Clinical Chemistry ◽

10.1373/clinchem.2009.136101 ◽

2010 ◽

Vol 56 (3) ◽

pp. 399-408 ◽

Cited By ~ 152

Author(s):

Stela Filipovic-Sadic ◽

Sachin Sah ◽

Liangjing Chen ◽

Julie Krosting ◽

Edward Sekinger ◽

...

Keyword(s):

Fragile X Syndrome ◽

Southern Blotting ◽

Trinucleotide Repeat ◽

Fragile X ◽

Clinical Samples ◽

Full Mutation ◽

Cgg Repeat ◽

Specific Pcr ◽

Cgg Repeats ◽

Pcr Technology

Abstract Background: Fragile X syndrome (FXS) is a trinucleotide-repeat disease caused by the expansion of CGG sequences in the 5′ untranslated region of the FMR1 (fragile X mental retardation 1) gene. Molecular diagnoses of FXS and other emerging FMR1 disorders typically rely on 2 tests, PCR and Southern blotting; however, performance or throughput limitations of these methods currently constrain routine testing. Methods: We evaluated a novel FMR1 gene–specific PCR technology with DNA templates from 20 cell lines and 146 blinded clinical samples. The CGG repeat number was determined by fragment sizing of PCR amplicons with capillary electrophoresis, and results were compared with those for FMR1 Southern blotting analyses with the same samples. Results: The FMR1 PCR accurately detected full-mutation alleles up to at least 1300 CGG repeats and consisting of >99% GC character. All categories of alleles detected by Southern blotting, including 66 samples with full mutations, were also identified by the FMR1 PCR for each of the 146 clinical samples. Because all full mutation alleles in samples from heterozygous females were detected by the PCR, allele zygosity was reconciled in every case. The PCR reagents also detected a 1% mass fraction of a 940-CGG allele in a background of 99% 23-CGG allele—a roughly 5- fold greater sensitivity than obtained with Southern blotting. Conclusions: The novel PCR technology can accurately categorize the spectrum of FMR1 alleles, including alleles previously considered too large to amplify; reproducibly detect low abundance full mutation alleles; and correctly infer homozygosity in female samples, thus greatly reducing the need for sample reflexing to Southern blotting.

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Learning-disabled Males With a Fragile X CGG Expansion in the Upper Premutation Size Range

PEDIATRICS ◽

10.1542/peds.97.1.122 ◽

1996 ◽

Vol 97 (1) ◽

pp. 122-126

Author(s):

Randi J. Hagerman ◽

Louise W. Staley ◽

Rebecca O'Conner ◽

Kellie Lugenbeel ◽

David Nelson ◽

...

Keyword(s):

Mental Retardation ◽

Fragile X Syndrome ◽

Size Range ◽

Cpg Island ◽

Fragile X ◽

Learning Disabled ◽

Full Mutation ◽

Cgg Repeat ◽

Responsible Gene ◽

Repeat Segment

There is a broad spectrum of clinical involvement in both boys and girls affected by fragile X syndrome. Although this disorder is best known as the most common inherited cause of mental retardation, it also can manifest as learning disabilities in individuals with IQs in the broad range of normal. Boys are usually retarded, and girls are usually learning disabled with fragile X syndrome.1 The responsible gene, fragile X mental retardation 1 (FMR1), was isolated in 1991, and the mutation was found to involve expansion of a trinucleotide (CGG) repeat segment. Individuals with fragile X syndrome have a CGG expansion of more than 200 repeats associated with hypermethylation of both the expansion and an adjacent CpG island (full mutation).2,3

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Analysis of unstable DNA sequence in FMR1 gene in Polish families with fragile X syndrome.

Acta Biochimica Polonica ◽

10.18388/abp.1996_4508 ◽

1996 ◽

Vol 43 (2) ◽

pp. 383-388

Author(s):

M Milewski ◽

M Zygulska ◽

J Bal ◽

W H Deelen ◽

E Obersztyn ◽

...

Keyword(s):

Fragile X Syndrome ◽

Dna Sequence ◽

Clinical Features ◽

Fragile Site ◽

Fragile X ◽

Fmr1 Gene ◽

Repeat Number ◽

Full Mutation ◽

Cgg Repeats ◽

Large Expansion

The unstable DNA sequence in the FMR1 gene was analyzed in 85 individuals from Polish families with fragile X syndrome in order to characterize mutations responsible for the disease in Poland. In all affected individuals classified on the basis of clinical features and expression of the fragile site at X(q27.3) a large expansion of the unstable sequence (full mutation) was detected. About 5% (2 of 43) of individuals with full mutation did not express the fragile site. Among normal alleles, ranging in size from 20 to 41 CGG repeats, allele with 29 repeats was the most frequent (37%). Transmission of premutated and fully mutated alleles to the offspring was always associated with size increase. No change in repeat number was found when normal alleles were transmitted.

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Screening for FMR1 CGG Repeat Expansion in Thai Patients with Autism Spectrum Disorder

BioMed Research International ◽

10.1155/2021/4359308 ◽

2021 ◽

Vol 2021 ◽

pp. 1-11

Author(s):

Areerat Hnoonual ◽

Charunee Jankittunpaiboon ◽

Pornprot Limprasert

Keyword(s):

Autism Spectrum Disorder ◽

Fragile X ◽

Single Gene ◽

Autism Spectrum ◽

Spectrum Disorder ◽

Fmr1 Gene ◽

Normal Male ◽

Cgg Repeat ◽

Cgg Repeats ◽

Normal Controls

Autism spectrum disorder (ASD) is a complex disorder with a heterogeneous etiology. Fragile X syndrome (FXS) is recognized as the most common single gene mutation associated with ASD. FXS patients show some autistic behaviors and may be difficult to distinguish at a young age from autistic children. However, there have been no published reports on the prevalence of FXS in ASD patients in Thailand. In this study, we present a pilot study to analyze the CGG repeat sizes of the FMR1 gene in Thai autistic patients. We screened 202 unrelated Thai patients (168 males and 34 females) with nonsyndromic ASD and 212 normal controls using standard FXS molecular diagnosis techniques. The distributions of FMR1 CGG repeat sizes in the ASD and normal control groups were similar, with the two most common alleles having 29 and 30 CGG repeats, followed by an allele with 36 CGG repeats. No FMR1 full mutations or premutations were found in either ASD individuals or the normal controls. Interestingly, three ASD male patients with high normal CGG and intermediate CGG repeats (44, 46, and 53 CGG repeats) were identified, indicating that the prevalence of FMR1 intermediate alleles in Thai ASD patients was approximately 1% while these alleles were absent in the normal male controls. Our study indicates that CGG repeat expansions of the FMR1 gene may not be a common genetic cause of nonsyndromic ASD in Thai patients. However, further studies for mutations other than the CGG expansion in the FMR1 gene are required to get a better information on FXS prevalence in Thai ASD patients.

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Beyond Trinucleotide Repeat Expansion in Fragile X Syndrome: Rare Coding and Noncoding Variants in FMR1 and Associated Phenotypes

Genes ◽

10.3390/genes12111669 ◽

2021 ◽

Vol 12 (11) ◽

pp. 1669

Author(s):

Cedrik Tekendo-Ngongang ◽

Angela Grochowsky ◽

Benjamin D. Solomon ◽

Sho T. Yano

Keyword(s):

Copy Number ◽

Trinucleotide Repeat ◽

De Novo ◽

Fragile X ◽

Copy Number Variants ◽

Repeat Expansion ◽

Full Mutation ◽

Cgg Repeat ◽

Testing Strategies ◽

Cgg Repeats

FMR1 (FMRP translational regulator 1) variants other than repeat expansion are known to cause disease phenotypes but can be overlooked if they are not accounted for in genetic testing strategies. We collected and reanalyzed the evidence for pathogenicity of FMR1 coding, noncoding, and copy number variants published to date. There is a spectrum of disease-causing FMR1 variation, with clinical and functional evidence supporting pathogenicity of five splicing, five missense, one in-frame deletion, one nonsense, and four frameshift variants. In addition, FMR1 deletions occur in both mosaic full mutation patients and as constitutional pathogenic alleles. De novo deletions arise not only from full mutation alleles but also alleles with normal-sized CGG repeats in several patients, suggesting that the CGG repeat region may be prone to genomic instability even in the absence of repeat expansion. We conclude that clinical tests for potentially FMR1-related indications such as intellectual disability should include methods capable of detecting small coding, noncoding, and copy number variants.

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Mosaicism in Fragile X syndrome: A family case series

Journal of Intellectual Disabilities ◽

10.1177/1744629521995346 ◽

2021 ◽

pp. 174462952199534

Author(s):

Wilmar Saldarriaga ◽

Laura Yuriko González-Teshima ◽

Jose Vicente Forero-Forero ◽

Hiu-Tung Tang ◽

Flora Tassone

Keyword(s):

Mental Retardation ◽

Fragile X Syndrome ◽

Fragile X ◽

Fmr1 Gene ◽

Molecular Testing ◽

Full Mutation ◽

Mild Phenotype ◽

Variable Expression ◽

Fragile X Mental Retardation ◽

Classic Phenotype

Fragile X syndrome (FXS) has a classic phenotype, however its expression can be variable among full mutation males. This is secondary to variable methylation mosaicisms and the number of CGG triplet repeats in the non-coding region of the Fragile X Mental Retardation 1 ( FMR1) gene, producing a variable expression of the Fragile X Mental Retardation Protein (FMRP). Here we report a family with several individuals affected by FXS: a boy with a hypermethylated FMR1 mutation and a classic phenotype; a man with an FMR1 gene mosaicism in the range of premutation (PM) and full mutation (FM), who has a mild phenotype due to which FXS was initially disregarded; and the cases of four women with a FM and mosaicism. This report highlights the importance of DNA molecular testing for the diagnosis of FXS in patients with developmental delay, intellectual disability and/or autism due to the variable phenotype that occurs in individuals with FMR1 mosaicisms.

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Reversion to Normal of FMR1 Expanded Alleles: A Rare Event in Two Independent Fragile X Syndrome Families

Genes ◽

10.3390/genes11030248 ◽

2020 ◽

Vol 11 (3) ◽

pp. 248

Author(s):

Elisabetta Tabolacci ◽

Roberta Pietrobono ◽

Giulia Maneri ◽

Laura Remondini ◽

Veronica Nobile ◽

...

Keyword(s):

Fragile X Syndrome ◽

Binding Sites ◽

Molecular Mechanisms ◽

Fragile X ◽

Rare Event ◽

The Other ◽

Fmr1 Gene ◽

Full Mutation ◽

Cgg Repeat ◽

Agg Interruptions

Fragile X syndrome (FXS) is mostly due to the expansion and subsequent methylation of a polymorphic CGG repeat in the 5’ UTR of the FMR1 gene. Full mutation alleles (FM) have more than 200 repeats and result in FMR1 gene silencing and FXS. FMs arise from maternal premutations (PM) that have 56–200 CGGs; contractions of a maternal PM or FM are rare. Here, we describe two unaffected boys in two independent FXS families who inherited a non-mosaic allele in the normal and intermediate range, respectively, from their mothers who are carriers of an expanded CGG allele. The first boy inherited a 51 CGG allele (without AGG interruptions) from his mother, who carries a PM allele with 72 CGGs. The other boy inherited from his FM mother an unusual allele with 19 CGGs resulting from a deletion, removing 85 bp upstream of the CGG repeat. Given that transcription of the deleted allele was found to be preserved, we assume that the binding sites for FMR1 transcription factors are excluded from the deletion. Such unusual cases resulting in non-mosaic reduction of maternal CGG expansions may help to clarify the molecular mechanisms underlying the instability of the FMR1 gene.

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Mosaicism for the fragile X syndrome full mutation and deletions within the CGG repeat of the FMR1 gene.

Journal of Medical Genetics ◽

10.1136/jmg.33.4.338 ◽

1996 ◽

Vol 33 (4) ◽

pp. 338-340 ◽

Cited By ~ 29

Author(s):

M Mila ◽

S Castellvi-Bel ◽

A Sanchez ◽

C Lazaro ◽

M Villa ◽

...

Keyword(s):

Fragile X Syndrome ◽

Fragile X ◽

Fmr1 Gene ◽

Full Mutation ◽

Cgg Repeat

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Fragile X Syndrome in Mentally Retarded Patients from Latvia

Proceedings of the Latvian Academy of Sciences Section B Natural Exact and Applied Sciences ◽

10.2478/v10046-009-0021-x ◽

2009 ◽

Vol 63 (1-2) ◽

pp. 70-72

Author(s):

Zanda Daneberga ◽

Zita Krūmiņa ◽

Baiba Lāce ◽

Daiga Bauze ◽

Natālija Proņina ◽

...

Keyword(s):

Mental Retardation ◽

Fragile X Syndrome ◽

Detection Rate ◽

Fragile X ◽

Mentally Retarded ◽

Normal Allele ◽

Cgg Repeat ◽

Repeat Structure ◽

Cgg Repeats ◽

Intermediate Alleles

Fragile X Syndrome in Mentally Retarded Patients from Latvia The aim of this study was to estimate the prevalence of FXS in Latvia and characterise the FMR1 CGG-repeat structure in Latvian patients exhibiting mental retardation. A group of 352 unrelated patients with mental retardation (MR) referred from clinical geneticists was screened by PCR for the normal allele. In a sample of 245 chromosomes the CGG repeat number was determined by Applied Biosystems protocol on ABI Prism 310. Prevalence of 29, 30, and 31 CGG repeats was found for the normal allele. Five affected patients were detected (detection rate 2.56%). AGG interspersion pattern analysis showed stability of transmission to the next generation for 12 intermediate alleles. The found detection rate of FXS in our survey among MR patients was similar to the detection rate reported in literature. Taking into account the number of confirmed FXS cases we suggest that FXS is still clinically unrecognized in paediatrician practice.

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Positive Emotional Support in Premutation Carrier Mothers of Adolescents and Adults With Fragile X Syndrome: Gene by Environment Interactions

American Journal on Intellectual and Developmental Disabilities ◽

10.1352/1944-7558-124.5.411 ◽

2019 ◽

Vol 124 (5) ◽

pp. 411-426 ◽

Cited By ~ 1

Author(s):

Sigan L. Hartley ◽

Leann S. DaWalt ◽

Jinkuk Hong ◽

Jan S. Greenberg ◽

Marsha R. Mailick

Keyword(s):

Fragile X Syndrome ◽

Emotional Support ◽

Fragile X ◽

Health Benefit ◽

Cortisol Awakening Response ◽

Cgg Repeat ◽

Premutation Carrier ◽

Cgg Repeats ◽

Gene By Environment Interactions ◽

Adolescents And Adults

Abstract We examined the benefit of emotional support on daily health in premutation carrier mothers of adolescents and adults with fragile X syndrome (n = 114), and whether this benefit was moderated by the mother's genetic status (FMR1 CGG repeat length). In an 8-day daily diary, maternal daily health was assessed subjectively through self-reported number of physical health symptoms and physiologically via cortisol awakening response. Multilevel lagged-day models indicated that premutation carrier mothers with midrange CGG repeats derived less health benefit from a day with high positive emotional support than those with lower or higher numbers of repeats within the premutation range. The data support the influence of both genetic and environmental influences on the health of this population.

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