Clinical features:
Over a 10-25 year
period HD becomes more severe, progressing to uncontrollable ceaseless
movements of the head, trunk and limbs. Speech becomes difficult to understand
and swallowing is difficult. Some people with HD experience personality
changes, impaired judgement, confusion, or
forgetfulness. Death follows, most frequently caused by pneumonia due to an
inability to cough effectively. The most common age of onset is between 30 and
50 years of age, although symptoms have appeared as young as 2 and as old as
70.
Inheritance: Autosomal dominant.
Affected individuals have a 50% chance to pass the gene to each of their
offspring.
Mutation information:
The mutation in the huntingtin gene is
an expansion of a CAG trinucleotide repeat in excess
of 39 repeats. An association has been reported between the size of the repeat
and the age of onset, however there is not enough data to support genotype:phenotype prognoses at
this time.
Indications and
benefits: Direct DNA testing is now recommended for confirmation of a diagnosis
of HD with or without a family history of this condition. People at risk for HD
who do not clearly carry a clinical diagnosis of HD are strongly recommended to
be tested through a counseling program approved by the Huntington Disease
Society of America. The pre-symptomatic testing protocol is designed to allow
at-risk individuals to prepare for the outcome of genetic testing. A special
consent form for HD testing must be completed prior to testing.
Test methodology: Samples are amplified for the HD gene region
(4p16.3) by extended polymerase chain reaction (E-PCR)* and sized on a gel.
Turnaround: Routine 2-3 weeks, Rush 7-10 days
Additional
resources: