In conclusion, our results show that hereditary essential
tremor has a bimodal age of onset, with a median age of onset in
the second dccade. Penetrance is virtually complete by the age
of 65 years and there were no examples of the   disease skipping
a generation. Men and woman were affected
with equal severity. The sex of the affected parent had no
influence on tremor severity or the extent of disability found
in their affected children. The condition did not produce
dystonic postures, isolated tremors of the head, legs, voice.
jaw, face or tongue or cause primary orthostatic or task
specific tremor. There were no cases of Parkinson's disease.
There was a possible association with classical migraine. Within
a single kindred some individuals had tremors that were alcohol
responsive, whilst others did not. Disability typically
commenced in the second or third decade and increased with the
duration of tremor and the age of the subject. Age at tremor
onset had no independent effect on outcome. Many individuals
with tremors of modest severity reported significant social
handicap. Physicians probably underestimate the effect of tremor
on patients' lives and overestimate the practical benefits of
the medical treatments available.
 
 Many previous studies of 'essential tremor' have been confused
by including patients with dystonia. The segregation ratio (0.46
for affected;total kin) and the median age of onset (15 years)
found in this study suggests that late onset sporadic cases of
postural tremor ('senile tremor') may have different etiologies
to hereditary essential tremor. Whether or not they all share
the same pathophysiology is another story.
 
Acknowledgements
 
 We wishs to thank Paul Atchison, Peter Asselman, Madhuri
Behari, Tom Britton, Richard Bedlington. John Caviness,
Elizabeth Chitty, Judit Mally and Tom Warner for their help with
various aspects of this study. This project was funded by a
grant from the Wellcome Trust.
 
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Received November 22, 1993. Revised February 11, 1994. Accepted
February 18. 1994
----------------------------------------------------------------------
 
Appendix 1
 
Activities of daily living
 
For each item the patients were asked to circle the number that
describes how easy or difficult it was for them to perform the
relevant activity.
 
                                   Percentage of patients
                                  reporting difficulty with
                                         each item
 
                                     Percent  Percent
                                     Index    Secondary
                                     Patients cases *
 
1  Cut food with a knife and fork
                     1   2   3   4    60       23
2  Use a spoon to drink soup
                     1   2   3   4    95       65
3  Hold a cup of tea
                     1   2   3   4    95       63
4  Pour milk from a bottle or carton
                     1   2   3   4    85       47
5  Wash and dry dishes
                     1   2   3   4    25       16
6  Brush your teeth
                     1   2   3   4    45       16
7  Use a handkerchief to blow your
   nose
                     1   2   3   4    20        9
8  Use a bath
                     1   2   3   4    25        9
9  Use a lavatory
                     1   2   3   4    20        7
10 Wash your face and hands
                     1   2   3   4    15        7
11 Tie up your shoelaces
                     1   2   3   4    60       23
12 Do up buttons
                     1   2   3   4    70       44
13 Do up a zip
                     1   2   3   4    50       19
14 Write a letter
                     1   2   3   4    85       58
15 Put a letter in an envelope
                     1   2   3   4    50       33
16 Hold and read a newspaper
                     1   2   3   4    70       37
17 Dial a telephone
                     1   2   3   4    65       19
18 Make yourself understood on the telephone
                     1   2   3   4    25       14
19 Watch a television
                     1   2   3   4     5        9
20 Pick up your change in a shop
                     1   2   3   4    80       44
21 Insert an electric plug into a socket
                     1   2   3   4    50       23
22 Unlock your front door with the key
                     1   2   3   4    55       30
23 Walk up and down stairs
                     1   2   3   4    30        9
24 Get up out of an armchair
                     1   2   3   4    25       12
25 Carry a full shopping bag
                     1   2   3   4    35       21
 
___________________________________________________________
 
Key: 1 = able to do activity without difficulty.
     2 = able to do the activity with a little effort.
     3 = able to do the activity with a lot of effort.
     4 = cannot do the activity by yourself.
 
* Percentage of those definite secondary cases who returned
completed questionaires (81.1% of all secondary cases).
 
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Appendix 2
 
(i) Please answer the following question by putting a circle
around the appropriate letter: A, B, C, or D.
 
Has your tremor stopped you:
 
(a) Shopping by yourself?                     A  B  C  D
(b) Eating out?                               A  B  C  D
(c) Accepting a party invitation?             A  B  C  D
(d) Doing your favourite sport or hobby?      A  B  C  D
(e) Traveling by public transport?            A  B  C  D
(f) Driving a car?                            A  B  C  D
(g) Applying for a job or promotion?          A  B  C  D
(h) Going on holiday?                         A  B  C  D
 
Key:
A = No
B = Yes, because you are EMBARRASSED by the tremor.
C = Yes, because of the PHYSICAL DIFFICULTIES produced by the tremor.
D = Yes, because of BOTH the PHYSICAL DIFFICULTIES and EMBARRASSMENT
    produced by the tremor.
 
(ii) The following question is only applicable if you have been
in full-time employment:
 
      As a result of the tremor have you ever had to
      change your job or take compulsory early retirement?
 
Please circle one of these answers:
 
           Yes      No      Not applicable
 
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                    END
 
John Cottingham    "KNOWLEDGE is of two kinds: we know a subject,
                    or we know where we can find information upon it."
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