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Journal of Clinical Endocrinology & Metabolism, doi:10.1210/jc.2005-0196
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The Journal of Clinical Endocrinology & Metabolism Vol. 90, No. 8 4607-4614
Copyright © 2005 by The Endocrine Society

Half of Clinically Defined Maturity-Onset Diabetes of the Young Patients in Denmark Do Not Have Mutations in HNF4A, GCK, and TCF1

A. Johansen1, J. Ek1, H. B. Mortensen, O. Pedersen and T. Hansen

Steno Diabetes Center and Hagedorn Research Institute (A.J., J.E., O.P., T.H), DK-2820 Gentofte, Denmark; Glostrup University Hospital (H.B.M.), DK-2600 Glostrup, Denmark; Faculty of Health Science (H.B.M.), University of Copenhagen, DK-2200 Copenhagen, Denmark; and Faculty of Health Science (O.P.), University of Aarhus, DK-8000 Aarhus, Denmark

Address all correspondence and requests for reprints to: Anders Johansen, M.D., Steno Diabetes Center, Niels Steensens Vej 2, DK-2820 Gentofte, Denmark. E-mail: adjo{at}steno.dk.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Aims/Hypothesis: Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic form of diabetes characterized by an autosomal dominant inheritance, an early clinical onset, and a primary defect in ß-cell function. The aims of the present study were to examine the prevalence and nature of mutations in the three common MODY genes, HNF4A, GCK, and TCF1, in Danish patients with a clinical diagnosis of MODY and to describe metabolic differences in probands with and without mutations in HNF4A, GCK, and TCF1.

Methods: Seventy-eight unrelated subjects of Danish Caucasian origin (29 men, 49 women) and their 351 family members were examined. The promotor and coding regions including intron-exon boundaries of HNF4A, GCK, and TCF1 were examined by denaturing HPLC and/or direct sequencing.

Results: We identified 29 different mutations in 38 MODY families. Fifteen of the mutations were novel. The variants segregated with diabetes within the families, and none of the variants were found in 100 normal Danish chromosomes. Our findings suggest a relative prevalence of 3% of MODY1 (two different mutations in two families), 10% of MODY2 (seven in eight), and 36% of MODY3 (21 in 28) among Danish kindred clinically diagnosed as MODY. No significant differences in biochemical and anthropometric measurements were observed at baseline examinations.

Conclusions: Forty-nine percent of the families carried mutations in the three examined MODY genes. Our findings highlight that unidentified MODY genes may play a central role for diabetes characterized by autosomal dominant transmission. Furthermore, baseline measurements of various anthropometric and biochemical variables are not appropriate markers of MODYX.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
MATURITY-ONSET DIABETES of the young (MODY) is a monogenic form of diabetes mellitus characterized by autosomal dominant inheritance, an early onset of the disease with at least one family member with diabetes diagnosed before the age of 25 yr, and an impairment of pancreatic ß-cell function (1). Presently, mutations in six different genes have been shown to cause MODY1–6. These are genes encoding hepatocyte nuclear factor (HNF)-4{alpha} (2), glucokinase (GCK) (3), HNF-1{alpha} (4), insulin promoter factor-1 (IPF-1) (5), HNF-1ß (6), and NeuroD1 (7, 8). Patients with MODY may erroneously be classified as having type 1 diabetes (T1DM) as well as type 2 diabetes (T2DM), and MODY may comprise up to 10% of diabetic patients without high-risk human leukocyte antigen haplotype originally classified as familial T1DM (9). In addition, mutations in MODY genes have been suggested to account for approximately 2–3% of patients with non-autoimmune diabetes (10) The diagnosis of MODY may warrant extra attention in juvenile and adolescent diabetes (11), and white children in the United Kingdom suffering from non-T1DM are as likely to have MODY diagnosed as T2DM (12). Although the true relative prevalence of the six distinct MODY subtypes is unknown and varies substantially in different populations (13, 14, 15, 16, 17, 18, 19), mutations in the genes encoding HNF-1{alpha} and GCK are by far the most prevalent. Mutations in GCK (MODY2) account for 7–41% (16, 17), whereas mutations in TCF1 (MODY3) may account for 11–63% (15, 19) of mutations in subjects with clinically diagnosed MODY. Mutations in HNF4A (MODY1) are less frequent and may account for 2–5% of subjects with MODY (15, 19). Only 26 families worldwide have been diagnosed with MODY1 (20). The prevalence of MODY patients with mutations in TCF2 (MODY5) is unknown, and although MODY5 has been considered very rare, it may comprise up to approximately 1% of British MODY patients and of Japanese diabetes patients with a strong family history of diabetes (15, 21). MODY5 has almost invariably been reported with concomitant nondiabetic renal dysfunction and renal cysts, and genital malformations are frequent (22, 23), which may prove to be a useful screening criterion (23). Mutations in IPF1 and NEUROD1 are rare and have been identified in single families. Interestingly, unknown MODY genes, known as MODYX, may be responsible for up to 79% of cases of MODY depending on sampling and the stringency of inclusion criteria (16). This finding suggests that additional MODY genes are likely to exist.

The aims of the present study were to elucidate the relative prevalence of the MODY subtypes caused by mutations in the genes HNF4A, GCK, and TCF1 encoding HNF-4{alpha}, GCK, and HNF-1{alpha}, respectively, in a Danish population with strict clinically defined MODY. Furthermore, we aimed at the baseline examination to characterize potential metabolic differences in probands with and without mutations in HNF4A, GCK, and TCF1.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Subjects

All patients identified in the outpatient clinic or referred to Steno Diabetes Center from Danish endocrinology departments and pediatric departments for genetic analysis of MODY during 1997 through 2003 fulfilling classical MODY criteria were included in the study. The probands or an affected family member to the proband had been diagnosed with diabetes mellitus that did not require insulin treatment for a period of at least 2 yr (to avoid patients with T1DM) or impaired glucose tolerance before the age of 25 yr. All probands had a family history of diabetes mellitus in at least two consecutive generations (64% had known diabetes in three or more consecutive generations). All probands were diabetic at the time of examination. A total of 78 unrelated probands (29 men, 49 women) with a clinical diagnosis of MODY and 351 members of their families participated in the present study. Probands had hyperglycemia first recognized at a mean age of 21.7 yr (range, 3–63 yr), and the mean age at examination was 33.9 yr (range, 10–73 yr). The mean age at examination was 41 yr for family members (range, 0–86 yr). Diabetes was diagnosed according to World Health Organization 1998 criteria. All participants were Danish Caucasian by self-report. Our study also involved an additional nine referred families of non-Caucasian ancestry fulfilling the MODY criteria and an additional eight Danish Caucasian probands with a MODY-like phenotype (i.e. lean, clinical onset of diabetes before the age of 25 yr, and treated with very low doses of insulin or with sulfonylureas) in whom family history was not available or involved only an affected sibling. These families were excluded from the epidemiological studies, yet the results from the mutation screening are reported.

Clinical examinations

All participants above the age of 18 yr were examined after an overnight fast lasting at least 10 h. In case of insulin therapy, neutral protamine hagedorn insulin was withdrawn 24 h before examination and rapid-acting insulin at least 10 h before examination. Oral hypoglycemic agents (OHA) were withdrawn 48 h before examination. All participants had fasting blood samples taken for measurements of plasma glucose, serum C-peptide, serum insulin, and glycosylated hemoglobin (HbA1C). Participants with no known history of diabetes had an additional standard 75-g oral glucose tolerance test performed. Data on retinopathy was evaluated by assessing the ophthalmological file of the patients (available for 60% of the probands). Nephropathy was diagnosed by testing for microalbuminuria and proteinuria. Screening for microalbuminuria was based on an initial sample of urine sampled after a minimum 10 h of fasting. In the case of a urine-albumin/urine-creatinine ratio above 30 mg/g, a 24-h urine collection was initiated. Microalbuminuria was diagnosed based on persistent albuminuria of 30–300 mg/24 h in at least two of three consecutive 24-h urine collections. End-stage renal failure was defined as the need for dialysis or renal transplantation. Neuropathy was based on vibration perception threshold (biothesiometry greater than 20 V) measured at the big toe.

Informed written consent was obtained before participation. The study protocol was approved by the regional Ethical Committees and was in accordance with the principles of the Declaration of Helsinki II.

Anthropometric measurements

The participants were weighed wearing light clothes and no shoes on an electronic scale and with results given to the nearest 0.05 kg. Height was measured to the nearest 0.5 cm with the subject standing against a wall-mounted stadiometer. Body mass index (BMI) was calculated as weight/height2. Hip and waist diameters were measured to the nearest 0.5 cm with the subjects standing using a nonextendable linen tape measure according to World Health Organization recommendations.

Biochemical assays

HbA1C was analyzed by principles of ion-exchange HPLC using Bio-Rad VARIANT HbA1C (Bio-Rad, Hercules, CA) (normal range, 4.1–6.4%). Serum triglycerides, serum total cholesterol, and serum high-density lipoprotein cholesterol were analyzed using enzymatic colorimetric methods (GPO-PAP and CHOD-PAP from Roche Molecular Biochemicals, Mannheim, Germany; and NEFA C from Wako, Neuss, Germany). The plasma glucose concentration was analyzed by a glucose oxidase method (Granutest; Merck, Darmstadt, Germany), serum-specific insulin (excluding des(31,32)- and intact proinsulin) and serum C-peptide was measured by time-resolved fluoroimmunoassay (AutoDELFIA; Perkin-Elmer-Wallac, Turku, Finland).

Genotyping

All exons (except 1a, 1b, and 7 in TCF1), the intron-exon boundaries, and the promoter regions of TCF1 and GCK were examined using denaturing HPLC as previously described (19). All variants identified by the denaturing HPLC scanning and PCR products from exon 1a, 1b, and 7 in TCF1 were examined by direct sequencing of both strands using ABI PRISM Dye Primer Cycle sequencing kit with AmpliTaq DNA polymerase FS and BigDye Terminator Cycle sequencing kit. Reactions were analyzed on an ABI PRISM 377 DNA sequencer (Perkin-Elmer, Foster City, CA.). HNF4A and its P1 promoter were sequenced with primers as described (24) except for exon 1c, where we used primers F, 5'- GCCAATTTCCAGCAAAAGTC-3', and R, 5'- CTTGCCGTCTCTCTGAACCT-3', and a PCR protocol using 1.5 mM MgCl2 and annealing at 60 C (24).

Statistical analysis

A general linear model was used to test variables (or transformed variables) for differences between patients with mutations in HNF4A, GCK, and TCF1 and patients with MODYX. Mutation status and sex were considered as fixed factors and age, BMI, and duration of diabetes as covariates. All phenotype analyses were performed using Statistical Package for Social Science (SPSS, Chicago, IL) version 12.0. A two-sided P value < 0.05 was considered significant.


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
The promoter and coding regions of the MODY1–3 genes including intron-exon boundaries were examined in 1) 78 patients with MODY, 2) eight patients with a MODY-like phenotype who did not fulfill stringent MODY criteria (no familial disposition or lack of reliable information of such), and 3) nine MODY patients of non-Caucasian ethnicity.

Mutations observed in group 2 or 3 are identified in Tables 1–3GoGoGo with symboled footnotes.


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  		TABLE 1. Mutations and polymorphisms in HNF4A in Danish subjects with MODY

 

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  		TABLE 2. Mutations and polymorphisms in GCK in subjects with MODY

 

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  		TABLE 3. Mutations and polymorphisms in TCF1 in Danish subjects with MODY

 
The results of the HNF4A screening are outlined in Table 1Go. We identified a total of three mutations: a previously described frameshift mutation in exon 2 and two novel mutations, Arg301Gln and Asp177fsinsG. The Arg301Gln variant cosegregated with diabetes in the family M131. For the case of the Asp177fsinsG variant, only the patient’s DNA was available for investigation.

The results of the GCK screening are outlined in Table 2Go. Eight mutations were identified in nine families. None of the identified mutations are previously reported except for the nucleotide substitution at the conserved splice donor site IVS1A+1G->T. Cosegregation with diabetes in the families was found for the IVS1A+1G->T mutation and for the mutations Leu122Pro, Glu395X, and I404fsdelAT. The Met8Ile, IVS8+1G->A, Gly178Glu, and Thr206Met mutations were investigated only in the affected proband because DNA from additional family members was not available for investigation.

The results of the TCF1 screening are outlined in Table 3Go. We identified 21 different mutations in 30 families. Six of 21 identified mutations were novel. Leu12Phe, Arg229Pro, Glu234X, Asp546Thr547fsdelGACA, and Val590fsinsA all cosegregated with diabetes in the families. The Gln124X variant was found in a MODY like proband.

None of the mutations in HNF4A, GCK, or TCF1 reported here were identified in 100 normal chromosomes from unrelated healthy Danish Caucasian subjects. Polymorphisms in HNF4A, GCK, and TCF1 are outlined in Tables 1–3GoGoGo. They have all been previously reported.

Clinical features of the 78 MODY probands are given in Table 4Go. No phenotypic differences were observed when comparing patients with mutations in HNF4A, GCK, or TCF1 and patients with MODYX (Table 4Go). However, two MODYX probands were found to be very insulin resistant compared with other MODYX probands and probands with mutations in HNF4A, GCK, or TCF1. The M9 and M42 probands had fasting circulating insulin levels of 74 pmol/liter and 274 pmol/liter, respectively (average for the total MODYX group was 48 ± 57 pmol/liter). Interestingly, two examined diabetic family members of M9 and one examined diabetic family member of M42 were also found to have high circulating fasting insulin levels (average for the examined family members, 80 ± 22 pmol/liter). Furthermore, one proband, M11-4, who was diagnosed with diabetes at the age of 17 yr, had a very high BMI of 40 kg/m2 but no additional features of the metabolic syndrome. She came from a family with confirmed diabetes in two generations, and her diabetic father, who was diagnosed with diabetes at the age of 30 yr, had a BMI of 35 kg/m2.


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  		TABLE 4. Phenotypes of probands with mutations in HNF4A, GCK, and TCF1 and with MODYX

 
The present findings suggest a relative prevalence of 3% of MODY1 (two different mutations in two families), 10% of MODY2 (seven in eight), and 36% of MODY3 (21 in 28) among Danish kindred clinically diagnosed as MODY. The majority of MODY families in Denmark (40 of 78) have no mutations in HNF4A, GCK, or TCF1. In Table 4Go, these are designated MODYX.

We also analyzed data excluding probands with fasting s-insulin above 31 pmol/liter (the median of fasting s-insulin in all MODY probands) to identify probands with MODY likely caused by a more severe insulin deficiency. Among these, 8% had MODY1, 4% had MODY2, 46% had MODY3, and 42% had MODYX.


   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
We have screened 78 Danish Caucasian MODY probands and identified 29 different mutations in 38 families (49%) fulfilling stringent MODY criteria. This means that in more than half of the Danish Caucasian MODY families we found no mutations in TCF1, GCK, or HNF4A. Fifteen of the mutations identified in the MODY families are private Danish mutations, and 12 of these have not been reported previously.

Two mutations in HNF4A were found in two families. The missense mutation Arg301Gln was novel and cosegregated with diabetes in family M131. The mutation substitutes an amino acid that is conserved between mouse, dog, and chimpanzee species and was not found in 100 normal Danish chromosomes. The Phe75fsdelT has previously been reported to cosegregate with diabetes in the large Danish M21 family (25). The proband carrying the Arg301Gln mutation was a lean woman at 29 yr of age diagnosed with diabetes 5.5 yr before examination. She was initially treated with metformin alone, but insulin had been added a few months before examination. She presented without diabetic complications, but her affected father had microalbuminuria upon examination. The proband from M21 carrying the Phe75fsdelT mutation also presented without complications after nearly 21 yr of diabetes, but several affected members of her family presented with microalbuminuria and one aunt carrying the mutation had severe complications with bilateral blindness and end-stage renal failure 34 yr after diabetes onset. Interestingly, the proband had been treated with sulfonylurea (glibenclamide) in very low doses for approximately 4 yr. However, she still experienced frequent hypoglycemia, which was also reported initially in two additional family members treated with sulfonylurea. It has consistently been reported that TCF1 mutation carriers may be extremely sensitive to treatment with sulfonylurea (26, 27, 28), but only scarce evidence exists of a similar phenotype in HNF4A mutation carriers (29).

A total number of seven mutations in GCK were identified in eight families. Six of these mutations were novel, and the variants Leu122Pro, Glu395X, and I404fsdelAT all cosegregated with diabetes in the affected families. An intronic variant IVS1A+1G->T that was previously reported in a family of Italian ancestry (30) was found in affected members in three generations of one Danish family. None of the reported mutations in GCK were found in 100 chromosomes screened in our laboratory, and all missense mutations altered amino acids that are conserved between mouse, dog, chicken, and chimpanzee species. Moreover, given the limited number of single-nucleotide polymorphisms reported in GCK (31), even the three mutations found exclusively in probands (IVS8+1G->A, Gly178Glu, and Thr206Met) are likely to be pathogenic. Intriguingly, three GCK mutation carriers were treated with insulin upon examination. Two of these were siblings aged 7 and 9 yr, respectively, carrying the I404fsdelAT mutation. Diabetes had been diagnosed 6 yr before examination with repeated mild elevations in fasting plasma glucose. They were treated with neutral protamine hagedorn insulin once daily in doses of less than 0.1 IU/kg. We performed an oral glucose tolerance test, revealing that they both had impaired glucose tolerance with an increment in plasma glucose of 3.7 and 1.3 mmol/liter, respectively. Upon genetic examination, insulin therapy was successfully terminated as evaluated by HbA1C at reexamination. The proband F302-3, carrying the Gly178Glu mutation of GCK, was a 72-yr-old very obese woman (BMI, 37.6 kg/m2) with diabetes lasting more than 45 yr and a family history of diabetes in at least four generations. She had been treated with diet for 38 yr, after which treatment with OHA was initiated. She had had extremely slow deterioration of glycemic control, and treatment with insulin was commenced only a few months before examination. She was the only patient among the GCK mutation carriers who had diabetic complications with mild peripheral neuropathy and microalbuminuria. There are several papers on the favorable prognosis for patients with MODY2 with microvascular complications being extremely rare or absent (17, 31, 32). Although retinopathy, proteinuria, and peripheral neuropathy have been reported in diabetic GCK mutation carriers (33), it could be hypothesized that the complications in the patient carrying the Gly178Glu mutation are a result of concurrent classical type 2 diabetes facilitated by obesity and aging.

Mutations in TCF1 were the most frequent explanation of MODY in the examined Danes. We found 20 mutations in 28 families. Five of these mutations were novel, and the Leu12Phe, Arg229Pro, Glu234X, Asp546Thr547fsdelGACA, and Val590fsinsA all cosegregated with diabetes in the families and caused changes in nucleotide sequences that are highly conserved across mouse, dog, chicken, and chimpanzee species. Consequently, we assume that they are all of functional importance. Baseline data on MODY3 probands are outlined in Table 4Go, and phenotypes varied with age at clinical onset ranging from four (abrupt onset, treated with insulin) to 44 (impaired glucose tolerance upon routine examination, treated with diet alone). Phenotypes did not only vary between families with different mutations but also varied immensely within families, and four family members (two men and two women) above the age of 30 yr (32–44 yr) carrying four different known MODY3 mutations were glucose tolerant upon examination, indicating the existence of other genetic variants modifying the phenotype of MODY3 patients. Insulin sensitivity as evaluated by homeostasis model assessment of insulin resistance (HOMA-IR) was within the normal range in these four persons. Like in previous reports, insulin therapy was common (65%) in patients with a MODY3 disease duration of more than 10 yr (19, 32). Diabetic complications (retinopathy, albuminuria, or nephropathy) were not reported in patients with diabetes lasting for less than 5 yr but were found in 63% of patients having a history of diabetes lasting for more than 10 yr (data not shown).

In the majority of Danish Caucasian MODY probands, we found no mutations in TCF1, GCK, or HNF4A. To discriminate between probands where a MODY mutation was likely to be found and probands likely to be diagnosed with MODYX, we aimed at assessing differences in metabolic markers and anthropometric measures at baseline examination. Baseline biochemical variables in probands (Table 4Go) showed no significant difference between MODYX patients and patients with mutations in TCF1, GCK, or HNF4A. However, as outlined in Table 4Go, the probands with MODYX had a tendency toward being more insulin resistant than patients with MODY1–3 as reflected in HOMA-IR. Comparing HOMA-IR in probands with MODYX and probands with TCF1 mutations alone was borderline significant with a P value of 0.06 (data not shown). Therefore, it is tempting to speculate that Danish patients with MODYX have a more T2DM-like phenotype, and we cannot fully exclude the possibility of early-onset T2DM among the MODYX families especially in the one family (M11) where diabetes cosegregates with obesity. However, there were no significant differences in age at clinical onset, BMI, waist to hip ratio, blood pressure, or cholesterol levels between the four groups (Table 4Go). Comparing MODYX probands with MODY3 probands alone did not alter this result. Highly interesting, though, is that two families had moderate to severe insulin resistance in affected members despite normal BMI in most of the members and absence of additional features of the metabolic syndrome suggestive of a subset of MODY patients with diabetes caused by a defect in the peripheral tissue rather than a ß-cell defect. The proportion of MODYX in this Danish MODY sample (51%) is close to what has previously been reported in the Czech Republic (48%) (19) and in Germany (45%) (13), but it is strikingly higher than what has been reported in French and British samples (16 and 13%, respectively) (15, 34, 35). It is possible that MODY in Denmark to a greater extent is caused by mutations in genes other than the TCF1, GCK, and HNF4A. However, the discrepancy, particularly in the prevalence of MODYX but also in the prevalence of mutations in various common MODY genes, may be explained by different criteria used in the selection for screening of MODY families. Excluding probands treated with insulin within a period of 2 yr after clinical diagnosis may have underestimated the prevalence of MODY3. However, because diabetes-associated autoantibodies were not available, omitting this criterion would have yielded a higher prevalence of MODYX because patients with familial type 1 diabetes might be included.

Among Danish Caucasian MODY-like patients who did not fulfill the strict MODY criteria, we identified one novel mutation in HNF4A, Asp177fsinsG, and two mutations in TCF1, Gln124X and Pro291fsinsC. The Gln124X mutation in TCF1 is novel, and the Pro291fsinsC is located in a suggested hot-spot region. These mutations are all likely to be diabetogenic. The codon 177 mutation in HNF4A is a frameshift mutation in exon 5, and the codon 124 mutation in exon 2 in TCF1 is a stop mutation resulting in a truncation of the HNF-1{alpha} protein. They are both located in nucleotide sequences that are highly conserved between species. The Pro291fsinsC mutation has been shown to cosegregate with MODY and to affect the transcriptional activity of HNF-1{alpha} in several studies (4, 36, 37). Furthermore, none of these mutations were found in 100 chromosomes of normal Danish control subjects.

Likewise, we report a novel mutation in exon 1a of GCK, Met8Ile, identified in a proband from a classical MODY family of Arabic ethnicity. Unfortunately, we could not test for cosegregation with diabetes in the family. The mutation was not found in 100 normal Danish chromosomes, and the peptide sequence was conserved across human, mouse, and dog. However, in previous studies, only two mutations in the ß-cell-specific exon 1a have been reported to cosegregate with diabetes (31), and at least two polymorphisms in this region (Asp4Asn and Ala10Ala) have been identified in French Caucasians (3). Therefore, we cannot exclude the possibility that this variant is a private polymorphism in Arabs.

The present study suggests that mutations in TCF1 are the most frequent cause of MODY in Denmark accounting for approximately one in three of the cases, whereas mutations in GCK are relatively rare. This is in line with previous reports from Northern Europe (3, 13, 15, 38) but conflicts with several, but not all, reports from Southern and Central Europe where mutations in GCK are by far the most prevalent cause of MODY with known molecular etiology (17, 19, 35, 38). Although we cannot exclude that the discrepancy in the observed prevalence of the various MODY subtypes reflects a specific genetic background in Danes, it is more likely to be explained by differences in the recruitment of families, in particular whether the ascertainment of MODY families is performed through adult or pediatric endocrinology departments. French MODY families were recruited primarily through pediatric departments by blood glucose screenings before the diagnosis of diabetes (34, 35, 39), and the MODY probands from the Czech Republic were also recruited predominantly from pediatric departments (62%) (19). In contrast, MODY probands were ascertained primarily from adult endocrinology departments in studies from Sweden, Germany, and United Kingdom (13, 15, 38), and in fact only approximately 25% of the families in the present study were recruited from pediatric departments. Asymptomatic MODY2 patients are less prevalent in studies recruiting probands from adult endocrinology departments, and indeed the widespread implementation of blood glucose testing in children in the French health care system has been hypothesized to attribute to the relatively high proportion of MODY2 (1). Finally, very strict MODY criteria include vertically transmitted diabetes in three generations. It could therefore be argued that applying such a criterion on the Danish families would significantly reduce the rather high proportion of MODYX families. Yet, analyzing data solely on families with confirmed diabetes in at least three generations (n = 50) only slightly increases the proportion of probands with mutations in TCF1 on behalf of a slight decrease in MODYX (data not shown). Likewise, in a subset of probands with MODY caused by an assumed more severe insulin deficiency, the prevalence of MODYX remained relatively high, i.e. 42%.

In conclusion, the present findings suggest a relative prevalence of 3% of MODY1, 10% of MODY2, and 36% of MODY3 among the examined Danish MODY patients. Forty-nine percent of the families carried mutations in the three common known MODY genes, suggesting that 51% of Danish families with clinical diagnosis of MODY may belong to unexplained MODYX. Baseline phenotypes were poor markers of MODYX. The relatively high proportion of MODYX compared with many similar studies points to the possibility that in Denmark, other yet unidentified genes may play a crucial role for diabetes characterized by autosomal dominant transmission. We identified a total of 15 novel mutations. In the MODY families 12 mutations of 29 (40%) were novel, and 15 mutations (52%) have been reported only in Danes, suggesting that the majority of MODY mutations in the Danish population may be local.


   Acknowledgments
 
We first and foremost thank the participating families. We also thank all physicians and clinical departments referring patients to Steno Diabetes Center for MODY examination.


   Footnotes
 
This work was supported by the Danish Medical Research Council, the Danish Diabetes Association, the Danish Heart Foundation, the Velux Foundation, European Economic Community (BMH4-CT98-3084, and QLRT-CT-1999-00 546), the Poul and Erna Sehested Hansen foundation, and Dronning Louises Børnehospitals forskningsfond.

First Published Online May 31, 2005

1 A.J. and J.E. contributed equally to this study. Back

Abbreviations: BMI, Body mass index; dHPLC, denaturing HPLC; GCK, glucokinase; HbA1C, hemoglobin A1C; HNF, hepatocyte nuclear factor; HOMA-IR, homeostasis model assessment of insulin resistance; MODY, maturity-onset diabetes of the young; OHA, oral hypoglycemic agent; T1DM, type 1 diabetes mellitus; T2DM, type 2 diabetes mellitus.

Received January 31, 2005.

Accepted May 20, 2005.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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