Huntington's chorea is associated with an unstable CAG trinucleotide expansion in exon 1 of a gene located on 4p16.3. The age of onset and penetrance are affected by the number of the CAG repeats. The authors are from the University of British Columbia and the Karolinska Institute.
|
CAG Repeats |
-2 SD |
Median Age |
+2 SD |
|
39 |
59 |
66 |
72 |
|
40 |
56 |
59 |
61 |
|
41 |
52 |
54 |
56 |
|
42 |
48 |
49 |
50 |
|
43 |
42 |
44 |
45 |
|
44 |
40 |
42 |
43 |
|
45 |
36 |
37 |
39 |
|
46 |
35 |
36 |
37 |
|
47 |
31 |
33 |
35 |
|
48 |
30 |
32 |
34 |
|
49 |
25 |
28 |
32 |
|
50 |
24 |
27 |
30 |
from Table 5, page 1207
Complete penetrance is seen when the CAG repeat size is >= 42. With 36-41 CAG repeats there is reduced penetrance but the penetrance increases with the increasing repeat lengths.
|
CAG Repeats |
Penetrance |
|
<= 35 |
0% |
|
36 |
33% |
|
37 |
<52%> |
|
38 |
66% |
|
39 |
89% |
|
40 |
98% |
|
41 |
99% |
|
>= 42 |
100% |
after Table 4, page 1207
where:
• The data in Table 4 for 37 CAG repeats showed a penetrance of 100% (4 out of 4). When the data is plotted in JMP a curve is generated whose equation gives 52% at CAG repeat size of 37.
Specialty: Genetics, Neurology
