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. 2020 Jan 28;11(2):136.
doi: 10.3390/genes11020136.

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

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Free PMC article

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

Karen Kengne Kamga et al. Genes (Basel). .
Free PMC article

Abstract

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.

Keywords: Africa; Cameroon; fragile X syndrome; full mutation; genetic counselling; premutation.

Conflict of interest statement

The authors declare no competing interest.

Figures

Figure 1
Figure 1
Flow chart of cascade testing for Fragile X Syndrome in Cameroon.
Figure 2
Figure 2
Description of our proband’s family. The number in brackets below the symbols as the number of CGG repeats in the FMR1 gene.
Figure 3
Figure 3
Distribution of Cytocine-Guanine-Guanine (CGG) repeat in the extended family.

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