The fragile-X syndrome: a growing gene causing familial intellectual disability.

Smith et al. (1994) wrote a story-style review. They pulled together early data on fragile-X syndrome.

The paper explains how the FMR-1 gene on the X chromosome gets too many CGG repeats. It lists the learning and behavior problems that follow.

No new lab work was done. The goal was to give doctors and scientists a clear picture of the newfound gene.

The authors show that fragile-X is the top inherited cause of intellectual disability in boys.

They map the trouble to one spot: the FMR-1 gene. When the gene is silenced, the brain protein FMRP is missing. That loss leads to delays, autism-like traits, and big ears.

Mulder et al. (2020) extends this gene story into daily practice. They trimmed and re-scored two autism checklists so they work better for kids who have fragile-X.

Capio et al. (2013) also extends the 1994 review. They bred Fmr1 knockout mice and showed the same social quirks seen in boys. The mouse work lets you test drugs before giving them to clients.

Honigfeld et al. (2012) looks related but focuses on extra sex chromosomes (XXY, XYY, XXYY). These groups also show social deficits, proving that many X-linked changes can hit social skills.

You now know fragile-X is a single-gene driver of ID and autism-like behavior. When a client has the diagnosis, expect language delay, hand flapping, and poor eye contact. Use the refined SCQ and SRS-2 cut-points from Mulder et al. (2020) to screen for ASD more accurately. If you run skill-building sessions, add visual cues and break instructions into tiny steps, because FMRP loss slows new learning.