Contribution of chromosome 1q21-q23 to familial combined hyperlipidemia in Mexican families.

doi: 10.1046/j.1529-8817.2003.00116.x
Contribution of Chromosome 1q21-q23 to Familial
Combined Hyperlipidemia in Mexican Families
A. Huertas-Va´zquez1, J. P. del Rinco´n2, S. Canizales-Quinteros1, L. Riba1, G. Vega-Herna´ndez3,
S. Ramı´rez-Jime´nez1, M. Auro´n-Go´mez2, F. J. Go´mez–Pe´rez2, C. A. Aguilar-Salinas 2 and
M. T. Tusie´-Luna1,∗
1Unidad de Biologı´a Molecular y Medicina Geno´mica del Instituto de Investigaciones Biome´dicas de la Universidad Nacional Auto´noma
de Me´xico y del Instituto Nacional de Ciencias Me´dicas y Nutricio´n Salvador Zubira´n, Mexico City
2Departamento de Endocrinologı´a y Metabolismo del Instituto Nacional de Ciencias Me´dicas y Nutricio´n Salvador Zubira´n, Mexico
City
3Direccio´n General de Servicios de Co´mputo Acade´mico, Universidad Nacional Auto´noma de Me´xico, Mexico City
Summary
Familial combined hyperlipidemia (FCHL) is the most common familial dyslipidemia, with a prevalence of 1-2% in
the general population. A major locus for FCHL has been mapped to chromosome 1q21-q23 in Finnish, Chinese,
German and US families. We studied seven extended Mexican families with 153 members, including 64 affected
subjects. A total of 11 markers were genotyped, including D1S104 which has been linked to FCHL in other studies.
Two point linkage analysis for the FCHL phenotype, and for the elevated triglyceride (TG) trait, allowing for
heterogeneity, gave a maximum HLOD of 1.67 (α = 0.49) and 1.93 (α = 0.43) at D1S2768 (2.69 cM proximal
to D1S104) respectively. Heterogeneity and non-parametric (NPL) multipoint analyses for the FCHL phenotype
and the TG trait showed maximum HLODs of 1.27 (α = 0.46) and 1.64 (α = 0.38), and NPLs of 4.00 (P =
0.0001) and 3.68 (P = 0.0003) near D1S2768, respectively. In addition, analysis of four candidate genes putatively
involved in the expression of FCHL showed no evidence of linkage for the LCAT gene or the APOA1/C3/A4/A5
gene cluster. However, we cannot exclude the participation of these genes, or the LIPC and LPL genes, as minor
susceptibility loci in the expression of FCHL, or the TG or elevated total cholesterol (TC) traits in our families. In
conclusion, our data confirm the involvement of a major susceptibility locus on chromosome 1q21-q23 in FCHL
Mexican families, consistent with findings in other populations.
Keywords: Genetic linkage, candidate genes, dyslipidemia, lipid metabolism
Introduction
Familial combined hyperlipidemia (FCHL)(MIM-
144250) is a common and heterogeneous disorder, char-
acterized by the presence of multiple lipoprotein phe-
notypes and a high risk for coronary artery disease
(CAD) (Goldstein et al. 1973), accounting for 10-20%
∗Corresponding author: Ma. Teresa Tusie´-Luna, M.D. Ph.D.
Unidad de Biologı´a Molecular y Medicina Geno´mica, Instituto
Nacional de Ciencias Me´dicas y Nutricio´n Salvador Zubira´n,
Vasco de Quiroga # 15, Colonia Seccio´n 16. Tlalpan, 14000
Me´xico D.F., Me´xico. Phone (52)(55) 56-55 00-11 or (52)55
73 12 00 Exts. 2251, 2252. FAX (00)(52)(55) 56-55-00-11.
E-mail: tusie@servidor.unam.mx
of the CAD patients under 60 years of age. FCHL is
characterized by the variable expression of both hyper-
triglyceridemia and hypercholesterolemia. One of the
characteristic features of FCHL is its variability in lipid
and lipoprotein pattern among family members (Bredie
et al. 1997). FCHL profiles are often associated with el-
evated APOB levels, an unfavourable decrease in HDL
cholesterol (HDL-C), and a preponderance of athero-
genic small-dense LDL particles (Nikkila et al. 1973;
Brunzell et al. 1983; Grundy et al. 1987; Soro et al. 2003;
Ayyobi et al. 2003). In addition, FCHL is associated with
hyperinsulinemia, impaired glucose tolerance, obesity
and insulin resistance (Eckel et al. 2001; Purnell et al.
2001).
C© University College London 2004 Annals of Human Genetics (2004) 68,419–427 419

A. Huertas-Va´zquez et al.
Although familial segregation in FCHL was initially
described as consistent with autosomal dominant trans-
mission (Goldstein et al. 1973), subsequent studies un-
covered a more complex and heterogeneous mode of in-
heritance (Castro-Cabezas et al. 1992; Cullen et al. 1994;
Aouizerat et al. 1999a), indicating that FCHL is an oli-
gogenic disorder where environmental factors can also
play a role in modulating its phenotype. Several ge-
netic surveys have been conducted in various ethnic
groups to identify susceptibility loci for FCHL, as well
as for its various subphenotypes (Wojciechowsky et al.
1991; Dallinga-Thie et al. 1997; Pajukanta et al. 1998;
Wijsman et al. 1998; Pajukanta et al. 1999; Aourizerat
et al. 1999a; Aourizerat et al. 1999b; Pei et al. 2000;
Coon et al. 2000; Naoumova et al. 2003; Eichenbaum-
Voline et al. 2003). However, its primary etiology re-
mains largely unknown.
Evidence for a major FCHL locus was first found
at chromosome 1q21-q23 in a survey of the Finnish
population (Pajukanta et al. 1998), and replication for
this locus was subsequently observed in Chinese,
German and US kindreds (Pei et al. 2000; Coon
et al. 2000). Linkage and or association to the
APOA1/C3/A4/A5 gene cluster (Wojciechowski et al.
1991; Dallinga-Thie et al. 1997; Wijsman et al.
1998; Aourizerat et al. 1999a; Naoumova et al. 2003;
Eichenbaum-Voline et al. 2003), and the lecithin choles-
terol acyltransferase (LCAT ) gene (Aourizerat et al.
1999b), have also been shown. Additionally, mutations
in the LPL gene have been associated with the pheno-
type (Reymer et al. 1995; Yang et al. 1995; Mailly et al.
1995; Deeb et al. 1996; Hoffer et al. 1996). These reports
suggest that these loci may contribute to the expression
of FCHL as modifier or susceptibility genes. Additional
evidence has shown that at least one of these loci (the
APOA1/C3/A4/A5 gene cluster) has an additional het-
erogeneous effect in a population in which linkage was
found for the 1q21-q23 locus (Coon et al. 2000).
Castellani et al. (1998) identified a mouse mutant
strain, HcB-19, that shares features with familial com-
bined hyperlipidemia. In this animal model the hyper-
lipidemia results from a mutation in the thioredoxin-
interacting protein (Txnip) gene at the Hyplip1 locus
on mouse chromosome 3, in a region syntenic to the
1q21-q23 FCHL locus in humans (Bodnar et al. 2002).
In this study, we evaluate the role of the chromosome
1q21-q23 locus, as well as different candidate genes, in
the FCHL phenotype in Mexican families. We report
evidence of linkage to the 1q21-q23 locus in our fami-
lies, confirming its contribution as a major locus in the
expression of FCHL. Additionally, we analyze human
TXNIP, the ortholog of Txnip in the murine model, as
a potential positional candidate.
Subjects and Methods
Subjects
Seven extended Mexican FCHL families with a history
of premature coronary heart disease (CAD), and the
presence of abnormal lipid profiles in several members
in consecutive generations, were included in this study.
These families were recruited from the Lipid Clinic of
the Instituto Nacional de Ciencias Me´dicas y Nutricio´n
Salvador Zubira´n (INCMNSZ) in Mexico City, and
comprise a total of 153 members including 64 affected
individuals (Figure 1). Affected status for the FCHL phe-
notype was assigned to individuals with elevated levels
of triglycerides (>90th percentile) (TG trait), and/or el-
evated levels of total cholesterol (>90th percentile (TC
trait), and elevated APO B levels (>90th percentile), ad-
justed for age and sex, defined according to a survey
of the Mexican population (Aguilar-Salinas et al. 2001;
Valles et al. 2002). The clinical characteristics of the sub-
jects are shown in Table 1. Additionally, at least one
first-degree relative should have an altered hyperlipi-
demic phenotype. Positive family history for premature
CAD was defined as a myocardial infarction (MI) or car-
diovascular disease before age 60. All lipid levels consid-
ered for affected individuals were prior to treatment. All
subjects completed a questionnaire about their previous
medical history, with emphasis on their cardiovascular
status, medication, and smoking and drinking habits.
BMI was determined for all subjects. Exclusion crite-
ria for affected status included the presence of tendon
xanthomas, renal disease, thyroid disorders, or a BMI >
30. Diabetic subjects were assigned an unknown status.
To circumvent problems of incomplete penetrance, and
because the FCHL phenotype is age dependent, nor-
molipemic individuals below age 20 were also classified
as unknown.
Informed written consent was obtained through
the attending physicians. The protocol for this study was
420 Annals of Human Genetics (2004) 68,419–427 C© University College London 2004

Contribution of Chromosome 1q21-q23 to FCHL in Mexican Families
Figure 1 Pedigrees of the seven families included in the study. Keys to the symbols are provided. Asterisks denote individuals
for whom DNA samples were available.
approved by the Institutional Committee of Biomedical
Research in Humans of the INCMNSZ.
Laboratory Analytical Methods
The Endocrinology and Lipid Metabolism Department
of the INCMNSZ performed all lipid and clinical lab-
oratory measurements using standardized procedures.
This laboratory is certified for standardization of tests
by the External Comparative Evaluation of Labora-
tories Program of the College of American Pathol-
ogists. Blood samples were taken after an overnight
fast (9-12 hours), following careful instructions to the
patients about the relevance of the required fasting.
C© University College London 2004 Annals of Human Genetics (2004) 68,419–427 421

A. Huertas-Va´zquez et al.
All analyses were performed with commercially avail-
able standardized methods. Glucose was measured us-
ing the glucose oxidase method, and HbA1c using
latex immunoagglutination inhibition (Bayer laborato-
ries). Total serum cholesterol and triglycerides were
measured using an enzymatic method (SERA-PAK®)
(CV 3.3%). HDL-C levels were assessed using phos-
photungstic acid and Mg2+ (CV 2.5%). LDL-C con-
centrations were estimated by the Friedewald formula
(Friedewald et al. 1972). Apolipoprotein B concen-
tration was measured by an immunonephelometric
method (CV 2.5%).
Genotyping
DNA was extracted from whole blood using a
phenol-free extraction protocol, adapted from Buf-
fone & Darlington (1985). Genotyping of microsatel-
lite markers was performed by PCR (polymerase
chain reaction) amplification, incorporating labelled
α-32P(dCTP) in the amplification reaction. The 1q21-
q23 locus was analyzed using the markers reported
by Pajukanta et al. (1998), and additional markers in
the region (D1S534, D1S2715, D1S1653, D1S2635,
D1S400) were selected from various databases (The
Genome Database: http://gdb.org; Center for Medi-
cal Genetics: http://research.marshfieldclinic.org). The
roles of four different candidate genes encoding en-
zymes putatively involved in the expression of FCHL
[hepatic lipase (LIPC), lipoprotein lipase (LPL), the
APOA1/C3/A4/A5 cluster and lecithin cholesterol
acyltransferase (LCAT )] were evaluated using intragenic
Table 1 Clinical characteristics of the
subjects
Variable Affected (mean±SD) Unafected (mean±SD) P
N (M/F) 64 (30/34) ∗ 52 (18/34) –
Age (years) 34.16± 16.68 33.02± 16.17 6.9 X 10−1
Body mass index 24.69 ± 4.17 23.09± 5.99 9.3 X 10−2
TC(mg/dl) 245.82± 26.24 170.37± 31.47 7.3 X 10−22
TG (mg/dl) 242.02± 89.44 110.08± 67.38 4.7 X 10−12
HDL-C (mg/dl) 40.17 ± 11.04 44.12± 10.49 3.8 X 10−2
LDL-C(mg/dl) 140.28 ± 41.49 106± 30.74 1.7 X 10−7
Apo B (mg/dl) 119.19± 25.61 79.63± 19.83 3.6 X 10−18
∗Lipid profile data were available for 153 individuals. There were 64 affected individuals
for the FCHL phenotype, and 52 unaffected individuals. Forty individuals were assigned
unknown status (See Subjects and Methods). For elevated TC, n = 46; for elevated TG,
n = 54. For elevated ApoB, n = 57.
or physically linked markers selected from the above
databases.
Linkage Analysis
Linkage analyses were performed with
GENEHUNTER-PLUS (Kong & Cox, 1997)
and GENEHUNTER-TWOLOCUS (Strauch et al.
2000). A model assuming a dominant pattern of
inheritance was used, with a gene frequency of 0.001
and 90% penetrance. Allele frequencies for all markers
were calculated from the non-related members of the
studied families.
Sequencing Analysis of the TXNIP Gene
The eight exons of the TXNIP gene, including exon-
intron junctions and a 1Kb proximal promoter re-
gion, were amplified by PCR from all seven probands
using specific primers based on GenBank entry
NM 006472.1. Sequencing reactions were performed
with Big Dye Terminator Kit v3 using a 3100 Genetic
Analyzer (Applied Biosystems).
Results
The clinical characteristics of the studied subjects are
listed in Table 1. Linkage analyses were performed
for the FCHL phenotype (as defined in the Sub-
jects section), and for the TG and TC traits, respec-
tively. Assuming heterogeneity, maximum two point
HLODs of 1.67 (α = 0.49), 1.93 (α = 0.43) and 0.72
422 Annals of Human Genetics (2004) 68,419–427 C© University College London 2004

Contribution of Chromosome 1q21-q23 to FCHL in Mexican Families
Table 2 HLOD and NPL values obtained for 5 markers spanning a 9.6 cM region at chromosome 1q21-q23∗ .
FCHL TG TC
Marker cM HLOD (α) NPL (p) HLOD (α) NPL (p) HLOD (α) NPL (p)
D1S2635 165.6 1.017 (.41) 0.97 (.16) 0.70 (.24) 0.35 (.355) −0.001 (0) 0.15 (.41)
APOA2 170.8 0.27 (.48) 1.09 (.14) 0.198 (.42) 1.07 (.126) −0.002 (0) 0.26 (.37)
D1S2768 172.9 1.67 (.49) 2.91 (.003) 1.93 (.43) 2.35 (.01) 0.72 (.22) 1.19(.104)
D1S104 175.2 0.43 (.28) 1.66 (.055) 0.70 (.40) 1.60 (.049) 0.58 (.31) 0.93 (.15)
D1S400 175.2 0.11 (.26) 3.06 (.002) 0.02 (.098) 2.58 (.005) 0.21 (.16) 1.54 (.056)
∗HLOD, Heterogeneity LOD score; NPL, Non-parametric LOD score; FCHL, combined phenotype; TG, elevated triglycerides
trait; TC, elevated total cholesterol trait. (α) proportion of linked families; (p) p value
(α = 0.22) were obtained at D1S2768 for the FCHL,
TG and TC traits, respectively (Table 2). This marker
is 2.6 cM centromeric to the D1S104 marker reported
by Pajukanta et al. (1998). Multipoint analyses yielded
a maximum HLOD of 1.27 (α = 0.46) and 1.64 (α =
0.38) for FCHL and TG, respectively, close to marker
D1S2768.
The contribution of individual families to the maxi-
mum two-point heterogeneity score is shown in Table 3.
For the FCHL phenotype, only one family exceeded a
LOD score of 2.0, while of the remaining six families,
five showed small positive LOD scores. For the TG and
TC traits, two families had LOD scores above 1.
Non-parametric multipoint analyses yielded maxi-
mum NPL scores of 4.0 (P = 0.0001), 3.6 (P = 0.0003)
and 1.38 (P = 0.07) for the FCHL, TG and TC traits,
respectively, at marker D1S2768.
We also analyzed the human TXNIP gene. TXNIP
is 16.5 Mb proximal to D1S2768, the marker with the
highest lod score. However, it lies within a 24 cM re-
gion with positive LOD score values, between D1S534
and D1S104 (119 to 160.8 Mb in the physical map).
TXNIP was considered a potential positional candidate
since it is the ortholog gene of Txnip at the Hyplip1 lo-
cus (syntenic to human chromosome 1q21-q23) of the
hyperlipidemic murine model. We performed sequence
analysis of the eight exons that constitute the gene, the
exon-intron junctions, and a 1 Kb proximal promoter
region, in all seven probands without identifying any
sequence changes.
Candidate genes encoding proteins involved in lipid
metabolism, LPL, LIPC, the APOA1/C3/A4/A5 gene
cluster, and LCAT , were additionally examined through
Table 3 Contributions of individual families (maximum para-
metric two-point LOD score) for the FCHL, TG and TC traits.
LOD score
Family Marker FCHL TG TC
1 D1S2768 2.01 1.93 1.70
2 D1S400 0.05 – –
3 – – – –
4 D1S104 0.50 0.84 0.77
5 D1S2768 0.28 1.19 0.0
D1S400 0.39 0.58 1.13
6 D1S2768 0.58 – –
7 APOA2 0.13 – –
linkage analysis to evaluate their possible contributions
to the FCHL phenotype, or TG and TC traits. Max-
imum HLODs of 0.29 (α = 0.16) and 0.19 (α =
0.19) were obtained for the LIPC gene (for FCHL
and TC), and 0.31 (α = 0.28) for the LPL gene (TG
trait). No evidence of linkage was found for the LCAT
gene or the APOA1/C3/A4/A5 gene cluster (Table 4).
A possible interaction between any of these candidate
genes with the 1q21-q23 locus was also evaluated (us-
ing GENEHUNTER-TWOLOCUS); no evidence of
interaction was found (data not shown).
Discussion
The present study in Mexican families substantiates
the previously reported involvement of the chromo-
some 1q21-q23 region as a major susceptibility locus for
FCHL (Pajukanta et al. 1998). Two-point linkage analy-
sis allowing for heterogeneity gave a maximum HLOD
of 1.67 (α = 0.49), 1.93 (α = 0.43) and 0.72 (α =
C© University College London 2004 Annals of Human Genetics (2004) 68,419–427 423

A. Huertas-Va´zquez et al.
Table 4 HLOD and α (proportion of linked families) values obtained for 4 candidate gene loci: APOA1/C3/A4/A5 cluster, lipoprotein
lipase, hepatic lipase and LCAT.
Gene FCHL TG TC Marker
HLOD (α) HLOD (α) HLOD (α) informativity
APOA1/C3/A4/A5 cluster
ApoAI (intragenic) −0.0004 (.0005) −0.0003 (.0004) 0.024 (.07) 0.38
D11S1989 −0.0001 (0) 0 (0) −0.0001 (.0001) 0.45
Lipoprotein lipase
LPL (intragenic) 0 (0) 0.31 (.28) 0 (0) 0.52
Hepatic Lipase
HL (intragenic) 0.299 (.16) −0.0001 (.0001) 0.19 (.19) 0.41
LCAT
D16S496 −0.0002 (.0001) 0.042 (.10) 0.006 (.07) 0.42
D16S2624 −0.0001 (.0001) 0.016 (.08) 0 (0) 0.4
0.22) for FCHL, TG and TC, respectively, for marker
D1S2768 (2.69 cM centromeric to D1S104) (Table 2),
while multipoint analysis yielded a maximum HLOD
of 1.27 (α = 0.46) and 1.64 (α = 0.38) for FCHL and
TG, respectively, close to marker D1S2768. It is inter-
esting to note that, as previously observed by Pajukanta
et al. (1998), our data also show higher scores predomi-
nantly for the FCHL phenotype and the TG trait. Our
results are consistent with those originally reported for
the Finnish population and then replicated in German,
Chinese and US populations (Pei et al. 2000; Coon et al.
2000). Sequencing analysis of human TXNIP, the or-
tholog murine Txnip and a strong positional candidate,
yielded no sequence changes in the eight exons that con-
stitute the gene, the exon-intron junctions, and a 1 Kb
proximal promoter region. This result suggests that the
gene responsible for FCHL in humans lies elsewhere
within this genomic region.
Although FCHL was initially thought of as an inher-
ited disorder with one major genetic locus, subsequent
studies have uncovered the complexity of the underlying
genetic causes of this common disease. Kinetic studies
suggest that the most common finding in patients with
FCHL is an increased secretion of VLDL triglycerides,
and associated APOB, raising the possibility that the pri-
mary defects involve triglyceride metabolism with sec-
ondary effects in cholesterol metabolism (Kane & Havel,
2001). However, there is also evidence that the FCHL
phenotype results in part from defects in lipoprotein
catabolism, with at least one clearly documented FCHL
kindred demonstrating impaired removal of both VLDL
and LDL (Aguilar et al. 1997). This metabolic hetero-
geneity supports the genetic evidence portraying this
condition as a highly complex and heterogeneous en-
tity.
Numerous genetic association and linkage stud-
ies have been performed in a variety of populations
and, with the exception of the chromosome 1q21-
q23 and the APOA1/C3/A4/A5 gene cluster, these
surveys have come up with widely different results
(Wojciechowsky et al. 1991; Dallinga-Thie et al.
1997; Pajukanta et al. 1998; Wijsman et al. 1998;
Pajukanta et al. 1999; Aourizerat et al. 1999a,b; Pei
et al. 2000; Coon et al. 2000; Naoumova et al. 2003;
Eichenbaum-Voline et al. 2003). Whereas the 1q21-q23
locus seems to have a predominant role in FCHL in
the studies with Finnish kindreds, it would seem that
it plays a lesser role in other ethnic groups as reported
for Chinese, German and US families (Pei et al. 2000;
Coon et al. 2000), and in the present study with Mexi-
can kindreds. However, the heterogeneity of the cohorts
used in these studies with respect to composition (larger,
more extended, families vs. primarily sib pairs), and
population-specific informativeness of the markers used,
could in part explain the varying magnitude of the re-
sults. Aouizerat et al. (1999a) did not find linkage to the
chromosome 1q21-q23 locus in a Dutch population, but
showed evidence of linkage to the APOA1/C3/A4/A5
gene cluster (Aouizerat et al. 1999a) and the LCAT gene
(Aouizerat et al. 1999b). Coon et al. (2000) replicated
linkage to the 1q21-q23 locus in a US population.
These authors also found a modest NPL value of 1.11,
p = 0.13, for the APOA1/C3/A4/A5 gene cluster.
However, using TWO-LOCUS analysis with markers in
the 1q21-q23 and the APOA1/C3/A4/A5 gene clus-
ter they found an additional heterogeneous effect for
424 Annals of Human Genetics (2004) 68,419–427 C© University College London 2004

Contribution of Chromosome 1q21-q23 to FCHL in Mexican Families
this locus (Coon et al. 2000). Recently, Naoumova et al.
(2003) and Eichenbaum-Voline et al. (2003) replicated
linkage for the APOA1/C3/A4/A5 gene cluster in a
Northern European population. These studies indicate
that these loci may act as either major loci, or suscepti-
bility or modifier genes, in the expression of the FCHL
phenotype in different ethnic groups.
In the present study, we also analyzed differ-
ent candidate genes encoding proteins essential for
lipid metabolism (LPL, LIPC, LCAT and the
APOA1/C3/A4/A5 cluster) that have previously
shown linkage or association to FCHL. No evidence
of linkage was found for the APOA1/C3/A4/A5 clus-
ter or LCAT , whereas nominal HLOD values were
obtained for the LIPC and LPL genes (for the FCHL
phenotype and the TC trait, and for the TG trait, re-
spectively) (Table 4). However, the size of the sample
studied does not allow us to exclude their participation
in the expression of FCHL in our families, especially
if their involvement is as minor susceptibility loci. The
sample size may also explain the lack of evidence when
testing for possible heterogeneity or interaction between
these four candidate loci and the 1q21-q23 region.
During the reviewing of this manuscript, a study
was published in the April issue of Nature Genetics by
Pajukanta et al. (2004). In this paper the authors also
rule out TXNIP as a candidate gene, and report asso-
ciation of upstream transcription factor (USF1), in this
same region, to the FCHL phenotype and the TG trait
predominantly, as is the case for this study. This supports
our results, as our maximum LOD score results for this
region are for marker D1S2768, which lies nearer to
USF1 than the D1S104 marker previously associated
with FCHL.
In conclusion, the fact that linkage of region 1q21-
q23 to FCHL has been found in populations of widely
different ethnicity provides strong evidence that this re-
gion harbours a major FCHL susceptibility gene. Our
results are the first report for a Latin American pop-
ulation, and add our cohort to those in which FCHL
is linked to chromosome 1q21-q23. The overall results
obtained in our study suggest genetic heterogeneity of
this disorder in the Mexican population. This observa-
tion is consistent, and seems to mirror the wide variation
observed in the literature, and suggests the involvement
of other as yet unidentified loci in the FCHL pheno-
type. An analysis to evaluate the participation of USF1
in a larger cohort of Mexican FCHL kindreds may prove
helpful in understanding its contribution to the expres-
sion of this complex disease in our population
Acknowledgements
We thank N. J. Cox and G. I. Bell for the critical read-
ing of this manuscript. This work was supported by grant
IN217501 from the Direccio´n General de Asuntos del
Personal Acade´mico, Universidad Nacional Auto´noma de
Me´xico, and grant 30774 from the Consejo Nacional de Cien-
cia y Tecnologı´a (CONACyT), Me´xico City. A.H.V., J. P. del
R. and S.C.Q. received support through CONACyT fellow-
ships.
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Received: 18 March 2004
Accepted: 22 April 2004
C© University College London 2004 Annals of Human Genetics (2004) 68,419–427 427