Fragile X is a CGG trinucleotide repeat expansion disorder (which like Huntington’s is a test favorite). The maternal uncle is the hint to the X-linked inheritance. Autism-like behaviors and relatively large head are common; large testicles only appear after puberty.

This is a corrected version of the post from @abhishek021196 below (https://nbmeanswers.com/exam/free120/1426#3919).

Fragile X syndrome X-linked dominant inheritance. Trinucleotide repeat in FMR1 gene = hypermethylation = decreased expression.

Most common inherited cause of intellectual disability (Down syndrome is the most common genetic cause, but most cases occur sporadically).

Findings: post-pubertal macroorchidism (enlarged testes), long face with a large jaw, large everted ears, autism, mitral valve prolapse, hypermobile joints.

Trinucleotide repeat expansion [(CGG) n ] occurs during oogenesis.

Learned something new today. " hand flapping" associates not only with hepatic encephalopathy, but also autism behavior.....

Anticipation is a genetic phenomenon in which disease traits are more severe and/or appear at earlier ages in later generations. Anticipation typically results from trinucleotide repeat expansions. Myotonic dystrophy, which features intergenerational anticipation, results from a trinucleotide repeat expansion of the DMPK gene in skeletal muscle cells that leads to progressive muscle dysfunction.

Fragile X syndrome X-linked dominant inheritance. Trinucleotide repeat in FMR1 gene = hypermethylation = Increased expression.

Most common inherited cause of intellectual disability (Down syndrome is the most common genetic cause, but most cases occur sporadically).

Findings: post-pubertal macroorchidism (enlarged testes), long face with a large jaw, large everted ears, autism, mitral valve prolapse, hypermobile joints.

Trinucleotide repeat expansion [(CGG) n ] occurs during oogenesis.