[Jalto2]

I have PD and my identical twin does not. Anyone heard of any studies with twins? Thanks. Jean

[GerryW]

Originally Posted by Jalto2

I have PD and my identical twin does not. Anyone heard of any studies with twins? Thanks. Jean

If you google Parkinson's twins you will find studies showing no genetic link, I am an identical twin and my brother doesn't have PD either.

[Tupelo3]

Originally Posted by Jalto2

I have PD and my identical twin does not. Anyone heard of any studies with twins? Thanks. Jean

Jean, this research is a little old, but it was a major study of genetics, twins and PD:

http://jama.jamanetwork.com/article....406#Joc81035f1

I think the main point for you is, if you don't have genetically caused PD (e.g LRRK2 mutation), there is no reason to think that your twin should be at any greater risk. I would moderate that opinion a little bit though and say, to the extent that twins share the same environmental lifestyle for an extended period of time, then there may be some increased risk as a result of environmental factors.

[johnt]

What is the probability of a twin getting PD given that one already has it? And what are the probabilities for other family members? These are interesting questions. We have a natural desire to know the implications of our illness for our family and the implications of their illness/wellness for us; and we can use knowledge of the distribution of PD within families to help find what causes the disease and to help identify therapies.

Tupelo3 writes:

"I think the main point for you is, if you don't have genetically caused PD (e.g LRRK2 mutation), there is no reason to think that your twin should be at any greater risk. I would moderate that opinion a little bit though and say, to the extent that twins share the same environmental lifestyle for an extended period of time, then there may be some increased risk as a result of environmental factors."

I would phrase things differently. My understanding of the research is that there is a considerably higher risk of a sibling getting the disease given that one has PD, and that the risk for a twin is higher still.

For instance, Marder et al. report:

"We estimated the degree of increased risk of PD in first-degree relatives of 221 PD probands with age of onset 50 years or younger and 266 PD probands with age of onset older than 50 years compared with the first-degree relatives of 409 control probands. Risk of PD was similar among first-degree relatives of early-onset PD probands (risk ratio [RR], 2.9 ...) and late-onset PD probands (RR, 2.7 ...) when each was compared with first-degree relatives of controls. However, siblings of early-onset PD probands were at markedly increased risk of PD compared with siblings of controls (RR, 7.9 ...), whereas parents of early-onset PD probands were not at significantly increased risk compared with parents of controls (RR, 1.7 ...). In late-onset families, both siblings (RR, 3.6; ...) and parents (RR, 2.5 ...) were at increased risk compared with control relatives."

And more recently Shino et al. [2] found:

"The cumulative incidence of PD was significantly higher among relatives of PD patients compared to relatives of controls (2.0 versus 0.7%; RR=3.4, 95% CI 1.9–5.9; p=0.0001)."

Table 3 in that paper is very interesting. It shows the relative risk values [RR] for various family relationships and other factors such as race and gender. The overall RR value for siblings is 5.4.

References

[1] Ann Neurol. 2003 Oct;54(4):507-13.
"Familial aggregation of early- and late-onset Parkinson's disease.
Marder K1, Levy G, Louis ED, Mejia-Santana H, Cote L, Andrews H, Harris J, Waters C, Ford B, Frucht S, Fahn S, Ottman R.
http://www.ncbi.nlm.nih.gov/pubmed/14520664

[2] Mov Disord. Nov 15, 2010; 25(15): 2587–2594.
"Familial Aggregation of Parkinson’s Disease in a Multiethnic Community-Based Case-Control Study"
Michael Y. Shino, M.D.,1,2 Valerie McGuire, Ph.D.,1 Stephen K. Van Den Eeden, Ph.D.,3 Caroline M. Tanner, MD, Ph.D.,4 Rita Popat, Ph.D.,1 Amethyst Leimpeter, M.S.,3 Allan L. Bernstein, M.D.,5 and Lorene M. Nelson, Ph.D.1,6
http://pubmedcentralcanada.ca/pmcc/articles/PMC2978761/

John

[Tupelo3]

John, I certainly wouldn't argue that there is a genetic component to PD, some of which we already know about (e.g mutations in lrrk2, park, etc) and some of which we don't.

However, the studies you cited were not controlled for genetics. Therefore, given that we know there is a genetic component to some forms of PD, you would certainly expect to find the increased familial risk these studies reported. There was no breakout of patients showing the results for those twins with known mutations and those without. The point I was trying to make was that without any genetic mutations, environmental factors were more like to determine the PD risk rather than the fact that they are twins.

Of course, I understand we can never rule out all genetic mutations as we don't currently know what they are. However, for those mutations we are aware of today, their overall occurrence is rather low, which would also indicate that environmental factors have more impact.