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9
| 3 | 2004
Klinisk Biokemi i Norden
a dominant effect over the non persistence trait.
Molecular genetic techniques, linkage, linkage dis-
equilibrium and haplotype analyses were applied
in Finnish families to assign a genetic variant of
lactase persistence (11). Majority of the participating
family members were tested using lactose tolerance
test (LTT) to define the phenotype and to deduce
the haplotype associated with lactase peristence.
Previously, lactase gene (LCT) was assigned to
chromosome 2q21-22 (12). Due to existing data
about low lactase activity in lactose malabsorption,
a candidate gene approach was chosen. Analysis of
microsatellite markers surrounding the LCT-gene
resulted in positive lod scores in the analysed fami-
lies. Based on linkage disequilibrium and haplotype
analysis, the most probable region was located
outside the LCT gene between markers D2S3013
and D2S3014 (Fig. 1). Sequence comparison of this
47 kb region in family members with three differ-
ent combination of haplotypes, homozygous for
lactase non persistence, heterozygous for lactase
persistence and homozygous for lactase persistence
resulted in the identification of a single nucleotide
polymorphism, cytosine (C) to thymidine (T) resid-
ing 13910 base pairs upstream of the LCT gene
that showed statistically significant association
with lactase persistence/non persistence status. C/C
–13910
-genotype at this locus was associated with
lactose malasorption and C/T
–13910
and T/T
–13910
–genotypes to lactose absorption. The association
has been confirmed in > 600 DNA samples isolated
from intestinal biopsy samples with verified disac-
charidase activities and lactase/saccharase-ratio
(L/S) (11,13,14). Furthermore, the frequency of the
C/C-13910 genotype was of similar range with
the previously published prevalence figures from
several populations including Finnish, French and
Somalia Utah (11). Recently, functional evidence
for the C/T
–13910
variant in the regulation of
lactase activity has been obtained in several studies
(13,15,16). Individuals with the persistent T
–13910
allele show several times higher LCT mRNA content
in their intestinal mucosa compared to that found
in individuals with the non-persistent C-13910
allele, suggesting regulation of the LCT gene at the
transcriptional level (13). This is in agreement with
recent
in vitro
studies reporting greater increase in
lactase promoter activity by the T
–13910
variant
(15,16). Comparison of lactose tolerance test (LTT)
and the C/T-13910-genotypes by pyrosequencing
in Swedish subjects show a statistically significant
correlation between the two tests (17).
Comparative analysis of disaccharidase values of
intestinal biopsies and the C/T-13910 genotypes in
Marker
Haplotype
Total
D2S3011
6
6
6
6
6
6
6
6
6
D2S3012
4
4
4
4
4
4
4
4
4
D2S3013
3
2
2
2
1
1
4
4
4
D2S3014
5
5
5
5
5
5
5
5
5
D2S3015
2
2
2
4
2
2
2
2
2
D2S3016
5
5
5
5
5
5
5
5
5
D2S3017
6
6
5
6
6
3
6
5
3
Lactase persistent alleles
20
4
1
2
2
1
1
1
1
33
Lactase non-persistent alleles
3
2
0
0
0
0
2
0
2
54
Figure 1
Enrichment of the founder haplotype (6-4-3-5-2-5-6) of lactase persistence in Finnish families
