Childhood obesity complicating the differential diagnosis of maturity-onset diabetes of the young and type 2 diabetes
Abstract
Objective: To describe a proband with features of type 2 diabetes who was found to have concomitant maturity-onset diabetes of the young (MODY) and the consequent multigeneration genetic analysis.
Design: Familial genetic analysis.
Setting: Tertiary university medical center.
Participants: The proband was a 13.5-yr-old boy with marked non-ketotic hyperglycemia, obesity, systolic hypertension, and insulin resistance. His mother, maternal aunt, grandmother, and great grandmother had diabetes; his father was obese and had early ischemic heart disease.
Interventions: Clinical examination, laboratory work-up, and DNA study.
Outcome measures: Mutation in hepatocyte nuclear factor-1α gene, the most common cause of MODY.
Results: The proband showed elevated C-peptide level and was negative for beta-cell antibodies. On genetic analysis for MODY, the 291fsinsC mutation was identified in all affected family members. A younger sister who was obese but had no signs of impaired glucose tolerance was also tested on the basis of these findings and was found to have the same mutation.
Conclusions: The patient, who presented with apparent type 2 diabetes, had concomitant MODY 3, inherited from his mother’s side, and some features of type 2 diabetes secondary to marked obesity. This combination probably caused an earlier and more severe presentation of the disease and had significant implications for medical management. A search for MODY mutations should be considered in patients with a history of diabetes in three generations of one side of the family, even those in whom the clinical picture resembles type 2 diabetes.
The current epidemic of childhood obesity (1) has been associated with an alarming rise in the prevalence of type 2 diabetes in the younger age-groups (2). The last 30 yr have also witnessed a rise in the prevalence of type 1 diabetes in children (3), with younger patients accounting for a growing proportion of all newly diagnosed cases of the disease (4).
There is also a third type of diabetes that occurs in youth, maturity-onset diabetes of the young (MODY), which is a non-ketotic type 2 diabetes characterized by an autosomal dominant inheritance and a primary defect in insulin secretion (5). An estimated 1–5% of all cases of diabetes in the USA and other industrialized countries are attributed to MODY (6). MODY can result from mutations in any of the seven different genes associated with the causative agents identified so far, each leading to a different subtype of the disease: the enzymes glucokinase (GCK; MODY 2) and carboxyl ester lipase (CEL; MODY 7) (7), and five transcription factors, namely hepatocyte nuclear factor-4α (HNF-4α; MODY 1), hepatocyte nuclear factor-1α (HNF-1α/transcription factor 1 (TCF1); MODY 3), insulin promoter factor-1 (IPF-1; MODY 4), hepatocyte nuclear factor-1β (HNF-1β/TCF2; MODY 5), and neurogenic differentiation factor-1 (NeuroD1; MODY 6) (8). The identification of the specific MODY subtype has important clinical implications for disease management and genetic counseling.
The main features that traditionally helped clinicians to distinguish MODY from type 2 diabetes were lack of obesity and other signs of the metabolic syndrome, such as insulin resistance and hypertension, in addition to a multigeneration vertical transmission owing to the autosomal dominant inheritance (9). However, studies have shown that the increased prevalence of childhood obesity may mask the differential diagnosis of the various types of diabetes presenting during childhood or adolescence (4, 10).
The present study describes a patient with a history of diabetes on one side of the family (four generations), who presented with marked non-ketotic hyperglycemia, obesity, systolic hypertension, and insulin resistance. To determine if the patient had concomitant type 2 diabetes and MODY, we performed a genetic analysis for mutations in HNF-1α, the most common cause of MODY (MODY 3) (11).
Methods and results
The proband was a 13.5-yr-old boy who presented to our clinic with headache of 5 d duration and elevated blood glucose levels, measured by his mother. The patient denied any polyuria, polydipsia, nocturia, or weight loss. The parents were non-consanguineous, of mixed Jewish Ashkenazi–Sephardi descent. The father was obese [body mass index (BMI) 30 kg/m2] with untreated hypertension and early ischemic heart disease; he had no family history of diabetes. The mother was diagnosed with diabetes at the age of 24 yr, during her first pregnancy, and was being treated with diet alone, achieving near-normal glycemic control [recent hemoglobin A1c (HbA1c), 6.4%]. Her BMI was within normal range (25.2 kg/m2), and she had no evidence of vascular complications. The patient’s maternal aunt, grandmother, and great grandmother had had diabetes from about age 30 yr, which was treated with diet alone. The grandmother currently had mild renal failure; the great grandmother died of myocardial infarction at the age of 56 yr.
The patient’s perinatal history was unremarkable, and his birth weight was 3.4 kg. He had been obese since the age of 6 yr but was otherwise healthy and receiving no medication. Body weight was 82 kg and height was 167 cm, yielding a BMI of 29.8 kg/m2, well above the 97th percentile for his age. Blood pressure was 158/81 mmHg and pulse, 87 beats/min. The obesity was generalized, and there was no acanthosis nigricans. Pubertal stage was Tanner 4. Fundus examination revealed no abnormalities.
Laboratory work-up
HbA1c levels were determined with the DCA 2000 analyzer (Bayer Diagnostics, Tarrytown, NY, USA) with a non-diabetic range of 4.3–6.3%, and serum C-peptide levels were measured by chemiluminescent immunometric assay using Immulite 2000 (DPC, Los Angeles, CA, USA). Beta-cell antibodies, including insulin autoantibodies (IAAs), 65 kDa glutamic acid decarboxylase (GAD) autoantibody, and insulinoma-associated islet tyrosine phosphatase autoantibody (IA-2 or ICA512AAs) were measured using validated radioimmunoassays (12).
Laboratory work-up was remarkable for blood glucose of 417 mg/dL and HbA1c of 11.8% (normal range, 4.3–5.8%); there was no evidence of diabetic ketoacidosis or ketonuria. Fasting lipid profile, liver function tests, and urinary microalbumin were all within normal range. Autoantibodies against ICA512AAs, GADs, and IAAs were negative. One day after diagnosis (before onset of medical therapy), fasting C-peptide level was elevated at 1489 pmol/L [normal range, 260–1320 pmol/L; mean (±SD) for adolescents in our center with type 2 diabetes mellitus (n = 22) was 1489±551 pmol/L; mean (±SD) basal level for adolescents with type 1 diabetes mellitus (n = 18), 340±147 pmol/L] (13). At that time point, glucose measured was 129 mg/dL.
Treatment and follow-up
The tentative diagnosis was type 2 diabetes, and treatment with diet, exercise, and 850 mg metformin t.i.d. was initiated. Within 3 months, the patient’s BMI decreased to 27 kg/m2, blood pressure dropped to 128/72 mmHg, and HbA1c level decreased to 6.7% and then stabilized at 7.4–7.8%. Because of the four-generation history of diabetes on his mother’s side, blood samples were collected from all living affected persons for molecular analysis of the MODY genes.
Written informed consent for DNA analysis was obtained from all family members, and the institutional Human Research Committee approved the protocol.
DNA analysis
Genomic DNA was isolated from peripheral blood by the salting-out technique (14). Thirteen pairs of primers were designed for the 10 exons and the corresponding intron–exon boundaries of the HNF-1α gene. Polymerase chain reaction (PCR)–denaturing gradient gel electrophoresis (DGGE) analysis was performed as previously described (15). All primers, as well as conditions for PCR and DGGE, are available upon request.
PCR and DGGE analysis of the entire coding region of the HNF-1α gene revealed abnormal migration in exon 4. To identify the specific location of the frameshift insertion, the two alleles were separated using the pGEM-T cloning kit (Promega, Madison, WI, USA). Sequencing of the two separate alleles showed that one allele was normal, whereas the other contained both a G–C transversion, which is a known polymorphism (16), and the common P291fsinsC mutation (16), creating a poly C tract of 10 cytosines instead of 8 or 9.
After detection of the MODY mutation, sulfonylurea treatment was added to metformin. HbA1c concentration dropped within 3 months from 7.5 to 6.7%.
On the basis of the genetic results, we extended the molecular analysis to the patient’s younger sister, who did not have diabetes or impaired glucose tolerance but was also obese. The findings yielded the same mutation, and she was started on a strict follow-up regimen in order to prevent early presentation of the disease.
Comment
The most common clinical presentation of MODY is mild, asymptomatic hyperglycemia in a non-obese child, an adolescent, or a young adult with a prominent history of diabetes on one side of the family, often in successive generations. Patients with MODY have a beta-cell dysfunction with decreased endogenous insulin secretion; they are not known to be insulin resistant (9, 11). By contrast, type 2 diabetes is a consequence of insulin resistance combined with an insulin-secretory defect. However, the progressive increase in the prevalence of childhood obesity in the western world has led to a frequent overlap of the clinical phenotypes of diabetes at presentation (10, 17, 18). This has created a gray area in diagnosis, making the differentiation among the types of diabetes increasingly challenging (4, 10). Recently, the term ‘double diabetes’ was coined to describe the co-presentation of type 1 and type 2 diabetes in obese children with proven autoimmunity against beta cells (4). The finding that type 1 diabetes may occur earlier in fatter children has prompted the still controversial ‘accelerator hypothesis’(19), which suggests that the presence of increased insulin resistance may accelerate the clinical appearance of autoimmune-mediated diabetes. We believe that this phenomenon could hold true for MODY as well. MODY usually presents as mild hyperglycemia that can go undetected for prolonged periods. Therefore, in many cases, the diagnosis is made rather late in adulthood, when diabetic complications may already be present, as in type 2 diabetes (20). However, in patients like ours with obesity-induced insulin resistance, MODY may manifest earlier and with more severe symptoms (10, 17, 18). Neither the mother nor the grandmother of our proband was obese, and they were diagnosed with diabetes during their third decade. However, the patient, an adolescent boy, was obese and had marked hyperglycemia, elevated C-peptide level, hypertension, and a favorable response to metformin therapy. As shown previously, fasting C-peptide level in patients with MODY is usually low and similar to basal levels in patients with newly diagnosed type 1 diabetes mellitus (9, 21).
In addition to the successive genetic transmission, other clinical hints of possible non-type 2 diabetes were the normal findings on lipid profile, liver function tests, and urinary microalbumin measurement (22).
It should be noted that we cannot rule out the contributory effect of the fetal nutritional environment and the mother’s gestational diabetes on the patient’s obesity and consequent insulin resistance. Previous studies reported that gestational diabetes and exposure to a diabetic environment in utero may be associated with impaired glucose tolerance or type 2 diabetes in the offspring, independent of genetic predisposition to type 2 diabetes. Furthermore, even in type 2 diabetes, there appears to be more history of diabetes on the mothers’ than on the fathers’ side, as in the present case. An excess of maternal transmission of diabetes is consistent with an epigenetic effect of hyperglycemia in pregnancy acting, in addition to genetic factors, to produce diabetes in the next generation (23, 24).
Numerous mutations have been identified in the HNF-1α gene in association with MODY 3 (16). The HNF-1α gene is composed of three functional domains: an amino terminal dimerization domain, a DNA-binding domain with Pit 1, Oct 1, Unc-86 (POU)-like and homeodomain-like motifs, and a carboxy-terminal transactivation domain (25). The mutation detected in the present family consisted of an insertion of cytosine in a poly C tract in exon 4. This site is a hot spot for mutations in exon 4, and the P291fsinsC mutation is the most prevalent mutation in MODY 3 (26). This frameshift mutation leads to the addition of an aberrant amino acid sequence as well as an immature stop codon at amino acid 316, giving rise to a truncated, inactive, protein that lacks the entire transactivation domain.
HNF-1α binds DNA as a dimer, and the mutant protein created by the 291insC mutation has been reported in in vitro studies to inhibit the wild-type protein by the formation of non-functional dimer (27). However, the elevated C-peptide level of our patient was not compatible with a supposedly dominant negative mutation. This finding is in line with the hypothesis that the mutant protein is removed because of the instability of the mutant messenger RNA or protein before it can dimerize with the normal protein (27).
The genetic diagnosis has direct clinical implications for this family. The first drug of choice for type 2 diabetes in adolescent patients, when diet and exercise alone fail, is metformin to reduce insulin resistance (28). However, patients with MODY 3 are sensitive to sulfonylureas (29). Therefore, in accordance with the genetic findings, we added sulfonylurea to the therapeutic regimen, leading to a further decline in HbA1C level by 1% within 3 months. The early diagnosis of other members of this family by genetic screening may help postpone the disease presentation, and the timely institution of specific therapy may help prevent long-term complications.
Conclusions
We describe a patient who presented with apparent type 2 diabetes and was found to have MODY 3 inherited from his mother’s side and insulin resistance secondary to marked obesity. This combination probably caused an earlier and more severe presentation of the disease and has significant implications for medical management.
These results suggest that a search for MODY mutations should be considered in patients with a history of diabetes in three consecutive generations of one side of the family, even those in whom the clinical picture resembles type 2 diabetes.
Acknowledgements
The study was supported by the following grants: D-Cure Diabetes Care in Israel; the Russell Berrie Foundation; Israel Diabetes Association; The Public Committee for Allocation of Estate Funds, Ministry of Justice, Israel; the Israel Association for the Study of Diabetes in Israel. The authors are grateful to Prof P. Froguel and Dr F. Vasseur (Institute Pasteur de Lille, Lille, France) for their generous contribution of the DNA samples with known mutations for use as internal controls. We thank Gloria Ginzach for preparing the manuscript.
