Fróðskaparrit - 31.12.2000, Page 54

58
SEARCH FOR SUSCEPTIBILITY LOCION SELECTED CHROMOSOMES
IN PATIENTS WITH PANIC DISORDER FROM THE FAROE ISLANDS
firm an interesting area, related to the Di-
George syndrome and Velocardiofacial
syndrome, but did show an interesting area
more distally on 22ql3 (Mors et al., 1999;
2000), Table 1.
Panic Disorder
For panic disorder, results have been de-
scribed in 1998, 1999, and 2000 (Degn et
ai, 1998; Wang et al., 1999; 2000). Our
data could not support the previously re-
ported association between panic disorder
and the cholecystokinin genes on chromo-
somal regions 3pter-p21 and llpl5,4
(Degn et al., 1998). Instead, our prelimi-
nary data point towards an interesting area
on chromosome 21 q22 (Wang et al., 2000),
Table 1.
Discussion
When mapping complex diseases, the
choice of population is a critical factor. A
genetically simplified isolate is probably
more useful than a diverse continental pop-
ulation (Editorial, 1998; Wright et al.,
1999). A basic requirement for LD map-
ping is a homogenous population, thus, iso-
lated population regions were sought. The
suitability of some of these isolated popula-
tions is at present being questioned (Arna-
son et al., 2000; Eaves et al., 2000) and,
more theoretically, the whole idea has been
disputed on the grounds that the study mod-
els are inadequate for diseases that are
probably multifactoral (Edwards, 1999).
However, the findings of a high degree of
homogeneity for cystic fibrosis and benign,
recurrent intrahepatic cholestasis in the
Faroe Islands (Tygstrup et al., 1999; á
Table 1. Areas ofpossible inlerest, sofar identified.
Øki higartil funnin, sum kunnu hava týdning.
Disorder Chromosome area
Bipolar affective disorder 18q23
10q26
Schizophrenia 22ql3
Panic disorder 21q22
Steig, 1999) could be taken as an indication
that the Faroe Islands might meet the crite-
ria of homogeneity.
In our genome screening, although not
fínished, we do see moderate numbers of
candidate regions. In a totally out-bred
population, the useful levels of LD will
rarely extend beyond 3 kb (Kruglyak,
1999) and no regions of LD would be ex-
pected with the marker density used in the
present study. On the other hand, a small
population size may tend to increase LD by
genetic drift and, in addition, the process
might be enhanced by population stratifica-
tion into small, inbred communities
(Wright et al., 1999). The result would be
many regions with LD. Whether the re-
gions detected in this study are false posi-
tives caused by stratification, or true, dis-
ease-bearing, identical-by-descent seg-
ments is not yet clear, but the small amount
of detected regions does signal a low de-
gree of stratification.
With a common forefather 10-12 genera-
tions ago, the possible size of a common
haplotype among persons with a disease
would require about 500 markers to ensure
its capture. However, the availability and
order of the markers could make some ar-
eas too long, with the result of missing the