Read the Case-Based Curriculum for Neurology Residents.

m. Case Comments
(by James Bemat, MD)
A. Assessmenl
1. What is the patient's medical condition and. prognosis? Wat lreatment
options exist?
The patient clearly is at risk for developing HD. There is a definire family hisrory
ofan affected parent with HD. Because HD is inherired as an autosomal dominant rair
with complere penerrance, the parienr has a 5ovo chance of having inherited rhe HD gene
and developing the disease. Most parienrs become symptomaric in their thirties or fonies
and die after a mean disease durarion of I 7 years. Treatments for HD may suppress the
choreiform movements, but no treatment for HD alters its progressive demeniia or irs
inexorably fatal course.
Numerous rests have been proposed for the presymptomatic d.iagnosis of HD. The
test with rhe greatesr positive predictive value (ppv) and negarive predictive va.lue (Npv)
is that which tests for the HD gene. Ir has been estimared thit, for the genetic test, both
the PPV and rhe NPV are in the 999o range. Therefore, unlike aI of thi prcviousry
proposed predictive rests' rhe genetic resr is a highly reliable predictor ofdevetoping HD.
2. Who is the appropriate d.ecision maker?
Surrogate decision making in HD becomes necessary as the disease progrcsses
because dementia worsens and patiens rose their decision making capacity.' Eiry in the
course of the illness, advance directives shourd be executed in anticipation of this
complication- No surrogates are necessary for testing in the presympromatic stage if the
patient is competent and is an adult.
& 4 Wat are the patient,s prefcrences? What are the preferences of the
family or surrogate decision makers?
Prcsymptomatic resring for HD should be performed only voluntarily at the
request of an at-risk patient. It should neither be ordered by others nor is ordering
coerced by others, such as in this case. It should not be ordered on minors who clnot
give valid consent.
5. Are there interests other than, and potentialry conJlicting with, those of the
patient urhich need to be considered?
In this case, the prospective inlaws insisr that genetic testing negative for HD be a
condition for approving their daughter's marriage. These third-party inierests conflict
with those of the patient, who is not ccnain that he wishes to know whether he is destined
to develop HD later in life. A similar siruation exists when pmspective cmploycrs or
insurcrs demand thar ar-risk patients be tesred. It is not ethically justifiable foi third
parties to require the performance ofa genetic test against the will of the patient.