X-Linked Disorders:

Fragile X syndrome is caused by a change in a gene called FMR1. FMR1 encodes for the protein FMRP, which is essential for early brain development. Fragile X syndrome is linked to multiple types of intellectual and emotional differences. The pathogenic change causes repeats of a piece of DNA in the region that codes for the FMRP protein. The three nucleotides (CGC) can repeat up to 200 times within the 5’-untranslated region of FMR1, eventually causing transcription of that gene to stop and preventing production of FMRP. This disorder has an X-linked dominant inheritance pattern, but shows reduced or incomplete penetrance, meaning that not everyone who has the genetic change will express the symptoms of the disorder (4).

Written by Abigail Sayers; Images by Abigail Sayers unless otherwise noted

Reviewed and Edited by Rachel Baer, MSc, and Andy McCarty, MS, LGC, CGC

Learn More About Genetics:

• Sample Types

• Prenatal and Fetal Testing

• Aneuploidies

• Cytogenetics

Learn More About the X Chromosome:

• The X Chromosome

• X and Y Chromosomal Aneuploidies

• DMD and BMD

• Hemophilia A

• Alport Syndrome

• Fabry Disease

• X-Linked Charcot-Marie-Tooth (CMTX)