Fróðskaparrit - 01.01.1998, Blaðsíða 6

12
HUMAN POPULATION GENETICS IN THE FAROE ISLANDS
Table 1. Probability p(m) that a random
chromosomal segment ofa ceratin size is shared
among eight descendants related g generations
ago.
Talva 1. Yvirlit yvir hvussu sannlíkt tað er (p(m)),
at eitt petti av kromosomi av ávísari stødd kann
finnast felags hjá 8 sjúkum, sum eru í familju g
ættarlið aftur í tíðina.
Size of segment P(m)
10 cM
g=5 0 out of 8 0.86157
1 out Of 8 0.12958
2 out of 8 0.00853
3 out of 8 0.00032
4 out Of 8 <0.00001
g=6 0 out of 8 0.93547
1 out of 8 0.06266
2 out of 8 0.00184
3 out of 8 0.00003
4 out of 8 <0.00001
15 cM
g=6 0 out Of 8 0.95382
1 out of 8 0.04523
2 out of 8 0.00094
3 out of 8 0.00001
4 out of 8 <0.00001
was between 17 and 33 years. All eight
held a bipolar diagnosis by ICD-10 and a
bipolar type I doagnosis by DSM-IV.
Genealogic assessment
Cases related six to ten generations ago
were sought in order to obtain an reason-
able size of shared chromosomal segments
around the putative disease gene(s). A ge-
nealogical search of church and civic
records of birth, marriages and deaths were
made for each patient. Lineages were
traced back as long as possible and the
shortest possible distance between any pair
of the patients parents were recorded. Exel-
lent church records exist from around 1750
while incomplete church and civic records
exist from even earlier. All eight patients
could be connecteđ in one or several ways.
The father in generation 1 was born around
1620, but the birth year of his wife is un-
known. The shortest possible distance be-
tween the 28 possible pairs made by con-
necting each person from the parent gener-
ation with each other were calculated. The
average number of generations relating two
patients were 6.2. Only two pairs were re-
lated as short as three or four generations
ago. In order to reconstruct the haplotypes
preferably both parents of the patients
should be collected and genotyped. How-
ever, due to the strict inclusion criteria
based on severity of phenotype, geography
and treatment response two parents could
only be collected for two of the eight bipo-
lar patients, while one parent could be col-
lected for the remaining five patients. Par-
ents still lack from the eighth patient. This
was not considered a major obstacle as hap-
lotypes can be inferred except for markers
in which the parent and child are identical
heterozygotes, in which case additional
markers may be genotyped if necessary.
Statistical evaluation
The affected persons may share a haplotype
identical by descent around a disease gene
or identical by descent by chance. If only
one or a few less informative markers are
genotyped in a chromosomal area the af-
fected persons may share marker alleles
identical by state.
The probability that the affected persons