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. Author manuscript; available in PMC: 2015 Jun 27.
Published in final edited form as: Adv Exp Med Biol. 2014;825:353–388. doi: 10.1007/978-1-4939-1221-6_10

Fig. 4.2.

Fig. 4.2

Proposed pathogenic mechanisms for microsatellite repeat diseases. Microsatellite expansions (red triangles) in noncoding (UTRs, small blue boxes; introns, black lines) regions may result in RNA (yellow boxes) gain-of-function (RNA GOF), protein (grey and colored circles) loss-of-function (protein LOF) or repeat-associated non-ATG (RAN) protein GOF (RAN GOF). In conventional coding regions (open reading frame, ORF), expansions might cause a protein GOF effect such as the CAG expansion in SCA3 which results in a polyGln (polyQ, brown circles) expansion that either accumulates in cellular inclusions or alters mutant ATXN3 (mATXN3) interactions. Note that RAN translation of the C9ORF72 GGGGCCexp repeat in ALS/FTD produces polyGlyAla (GA), polyGlyPro (GP) and polyGlyArg (GR) dipeptide repeat proteins due to the recognition an RNS secondary structure (red hairpin) by the ribosome (orange ellipsoids).