Polyalanine -expansion diseases

Polyalanine (A ) expansions also give rise to disease phenotypes (Section 5). In eight of these diseases, the expansion is in a transcription factor and the disease phenotype is evident at birth. If transcription factor dysfunction contributes to Q -expansion diseases, then a hypothesis explaining the disease phenotype must account for the fact that the disease phenotype is present at birth in the A -expansion diseases, but is typically adult onset in Q -expansion diseases. 

Diseases Due to a Coding Trinucleotide Expansion—Polyalanine (A )-Expansion Diseases... 

Twelve or more additional triplet repeat diseases, many with neurological symptoms, have been identified (Table 26-4).405 407a These involve other trinucleotide repeats 5 -(GCG) , 5 -(CTG) , 5 -(GAA) , and 5 -(CAG) . In synpolydactyly, an inherited developmental defect causing malformation of hands and feet, an expansion of a GCG trinucleotide occurs within the gene HoxD 13. This results in incorporation of a polyalanine tract near the N terminus of the protein.408 Myotonic dystrophy DM1 (Box 19-A) results from expansion of CTG to 6 kbp or more within the untranslated 3 region of a gene for cAMP-dependent protein kinase.405 The mRNA transcripts accumulate... 

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