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.
Highlights
IntroductionFragile X Syndrome (FXS) is the most common monogenic X-linked condition which causes variable degrees of Intellectual Disability (ID), autism spectrum disorder (ASD), delay in acquisition of speech and other cognitive skills; affecting one in 7143 males and one in 11,111 females [1,2,3,4,5]
Fragile X Syndrome (FXS) is the most common monogenic X-linked condition which causes variable degrees of Intellectual Disability (ID), autism spectrum disorder (ASD), delay in acquisition of speech and other cognitive skills; affecting one in 7143 males and one in 11,111 females [1,2,3,4,5].Some individuals with FXS may present characteristics of facial appearance such as, a large forehead and prominent ears
Fragile X Syndrome is associated with Cytosine-Guanine-Guanine (CGG) repeat sequence expansion located in the 50 untranslated region (UTR) in the Fragile X Mental Retardation gene 1 (FMR1), at the
Summary
Fragile X Syndrome (FXS) is the most common monogenic X-linked condition which causes variable degrees of Intellectual Disability (ID), autism spectrum disorder (ASD), delay in acquisition of speech and other cognitive skills; affecting one in 7143 males and one in 11,111 females [1,2,3,4,5]. Some individuals with FXS may present characteristics of facial appearance such as, a large forehead and prominent ears. Some of these signs may only occur after puberty which is the case of adolescent males who may develop macro-orchidism. Xq27 position [8,9] This expansion which accounts for over 98% of all FXS cases exist in four allelic
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