Comment to letter: "Identical twins with LRRK2 mutation discordant for Parkinson's disease"

Modelling idiopathic Parkinson disease as a complex illness can inform incidence rate in healthy adults: the PR EDIGT score

Fifty-five years after the concept of dopamine replacement therapy was introduced, Parkinson disease (PD) remains an incurable neurological disorder. To date, no disease-modifying therapeutic has been approved. The inability to predict PD incidence risk in healthy adults is seen as a limitation in drug development, because by the time of clinical diagnosis ≥ 60% of dopamine neurons have been lost. We have designed an incidence prediction model founded on the concept that the pathogenesis of PD is similar to that of many disorders observed in ageing humans, i.e. a complex, multifactorial disease. Our model considers five factors to determine cumulative incidence rates for PD in healthy adults: (i) DNA variants that alter susceptibility (D), e.g. carrying a LRRK2 or GBA risk allele; (ii) Exposure history to select environmental factors including xenobiotics (E); (iii) Gene-environment interactions that initiate pathological tissue responses (I), e.g. a rise in ROS levels, misprocessing of amyloidogenic proteins (foremost, α-synuclein) and dysregulated inflammation; (iv) sex (or gender; G); and importantly, (v) time (T) encompassing ageing-related changes, latency of illness and propagation of disease. We propose that cumulative incidence rates for PD (PR ) can be calculated in healthy adults, using the formula: PR (%) = (E + D + I) × G × T. Here, we demonstrate six case scenarios leading to young-onset parkinsonism (n = 3) and late-onset PD (n = 3). Further development and validation of this prediction model and its scoring system promise to improve subject recruitment in future intervention trials. Such efforts will be aimed at disease prevention through targeted selection of healthy individuals with a higher prediction score for developing PD in the future and at disease modification in subjects that already manifest prodromal signs.

Switched-at-birth twins in the Canary Islands: revisited

Switched-at-birth twins from Las Palmas, Gran Canaria in Spain drew international attention in May 2008 following news reports of their unexpected reunion. I visited Las Palmas in September 2009 to research this case and presented the findings in Segal and Blandón-Gitlin (Twin Research and Human Genetics, Vol. 13, 2010, pp. 115–119) and in a book, Someone Else's Twin: The True Story of Babies Switched at Birth (Segal, Prometheus Books, Amherst, New York, 2011). I traveled again to Las Palmas in November 2012 to meet with the twins, their families, and their attorneys and have updated my findings in this article. Next, new twin research on Parkinson's disease discordance, neonatal surgery, double embryo transfer in a cynomolgus monkey, and a convention conundrum are presented. Media highlights concerning twin inventors, basketball players, rappers, designers, musicians, and birth intervals are also summarized.