Is there an excess in maternal transmission of NIDDM?

Heritability and Genetics of Type 2 Diabetes Mellitus in Sub-Saharan Africa: A Systematic Review and Meta-Analysis

OBJECTIVES

Sub-Saharan Africa (SSA) is observing an accelerating prevalence rate of type 2 diabetes mellitus (T2DM) influenced by gene-environment interaction of modifiable and nonmodifiable factors. We conducted a systematic review and meta-analysis on the heritability and genetic risk of T2DM in SSA.

METHODS

We reviewed all published articles on T2DM in SSA between January 2000 and December 2019 and available in PubMed, Scopus, and Web of Science. Studies that reported on the genetics and/or heritability of T2DM or indicators of glycaemia were included. Data extracted included the study design, records of family history, pattern and characteristics of inheritance, genetic determinants, and effects estimates.

RESULTS

The pattern and characteristics of T2DM heritability in SSA are preference for maternal aggregation, higher among first degree compared to second-degree relatives; early age-onset (<50 years), and inherited abnormalities of beta-cell function/mass. The overall prevalence of T2DM was 28.2% for the population with a positive family history (PFH) and 11.2% for the population with negative family history (NFH). The pooled odds ratio of the impact of PFH on T2DM was 3.29 (95% CI: 2.40-4.52). Overall, 28 polymorphisms in 17 genes have been investigated in relation with T2DM in SSA. Almost all studies used the candidate gene approach with most (45.8%) of genetic studies published between 2011 and 2015. Polymorphisms in ABCC8, Haptoglobin, KCNJ11, ACDC, ENPP1, TNF-α, and TCF7L2 were found to be associated with T2DM, with overlapping effect on specific cardiometabolic traits. Genome-wide studies identified ancestry-specific signals (AGMO-rs73284431, VT11A-rs17746147, and ZRANB3) and TCF7L2-rs7903146 as the only transferable genetic risk variants to SSA population. TCF7L2-rs7903146 polymorphism was investigated in multiple studies with consistent effects and low-moderate statistical heterogeneity. Effect sizes were modestly strong [odds ratio = 6.17 (95% CI: 2.03-18.81), codominant model; 2.27 (95% CI: 1.50-3.44), additive model; 1.75 (95% CI: 1.18-2.59), recessive model]. Current evidence on the heritability and genetic markers of T2DM in SSA populations is limited and largely insufficient to reliably inform the genetic architecture of T2DM across SSA regions.

Maternal history of diabetes is associated with increased cardiometabolic risk in Chinese

OBJECTIVE

Positive family history is associated with increased type 2 diabetes (T2D) risk, and reflects both genetic and environmental risks. Several studies have suggested an excess maternal transmission of T2D, although the underlying mechanism is unknown. We aimed to examine the association between maternal diabetes and cardiometabolic risk in the offspring.

METHODS

Parental history of diabetes and clinical data including anthropometric traits, fasting plasma glucose and insulin (FPG, FPI), blood pressure and lipid profile were collected from 2581 unrelated Chinese offspring (2026 adolescents from a population-based school survey and 555 adults from a community-based health screening programme). A subset of subjects (n=834) underwent oral glucose tolerance test to measure the glucose and insulin concentrations at 0, 15, 30, 60 and 120 min for evaluation of the areas under the curve (AUC) of glucose and insulin at 0-120 min, homoeostasis model assessment of insulin resistance (HOMA-IR) and bell-cell function, insulinogenic index, insulin sensitivity index (ISI) and oral disposition index (DI).

RESULTS

A positive parental history of diabetes was associated with increased risk of obesity (odd ratios (OR) (95% confidence interval (CI))=1.48 (1.10-2.00)), central obesity (OR (95% CI)=1.67 (1.21-2.32)), higher FPI, HOMA-IR, 2-h insulin, AUC of glucose at 0-120 min, triglycerides, reduced ISI and DI. Compared with individuals without parental diabetes, offspring with diabetic mother had significantly increased risk of obesity (OR (95% CI)=1.59 (1.07-2.35)), central obesity (OR (95% CI)=1.88 (1.23-2.88)), higher glucose levels and BP, were more insulin resistant but also had impaired first-phase insulin response and worse lipid profile. However, paternal history of diabetes had no effect on any of the studied traits, except higher body mass index, waist circumference in females and FPG.

CONCLUSIONS

Our findings suggested that maternal history of diabetes conferred increased risk of cardiometabolic abnormalities, and was associated with both insulin resistance and impaired first-phase insulin secretion. Further investigation into the mechanism of transgenerational diabetes is warranted.

Familial Clustering of Type 2 Diabetes among Omanis

OBJECTIVE

The aim of this study was to screen Omani individuals for the familial aggregation of type 2 diabetes mellitus.

METHODS

A random cohort of 1182 Omani individuals visiting the Family Medicine Clinic at Sultan Qaboos University Hospital (SQUH), Muscat, Oman, for regular medical checkup, aged ≥40 years, were sampled. Patients were categorized into three groups: (1) individuals who claim not to have diabetes and had no family history of diabetes; (2) individuals who claim not to have diabetes but had family history of diabetes; (3) individuals with diabetes. Only 16% of these Omani individuals had no diabetes and no family history of diabetes. Another separate random cohort of 234 Omani type 2 diabetes mellitus patients, from the Diabetes Clinic at SQUH, were interviewed and questioned about their family history of type 2 diabetes mellitus.

RESULTS

Ninety five percent of the patients had a family history of diabetes. Eighty percent had first degree relatives with diabetes and 46% had second degree relatives with diabetes. At least one parent with diabetes was reported among 55% of these diabetics, while maternal diabetes (55%) was found to be higher than paternal diabetes (47%). However, only 15% had both parents with diabetes. Furthermore, almost half of the 234 diabetics were having at least one of the following relatives with diabetes: brother, sister, aunt or an uncle.

CONCLUSION

The findings of this study confirm familial aggregation of diabetes among the Omani population. Compared to other populations, familial aggregation of type 2 diabetes mellitus among Omanis is relatively very high, and is perhaps due to the very high degree of consanguinity among Omanis. Since almost everyone seems to have a genetic predisposition to diabetes, the dramatic lifestyle changes over the past 25 years, could tip the population into an epidemic of type 2 diabetes mellitus.

[Long term outcome in children of mothers with gestational diabetes]

OBJECTIVES

To appreciate, in epidemiological studies, the impact of fetal exposure to gestational diabetes on the long term outcome of the offspring (type 2 diabetes, overweight and obesity, metabolic syndrome and neurological complications).

METHODS

A systematic search was conducted in Medline between January 1990 and April 2010. Prospective studies (follow-up of the offspring born of mothers with gestational diabetes) and retrospective studies (questionnaire about the parents'history of diabetes in diabetic patients) were searched and analysed.

RESULTS

The fetal exposure to maternal gestational diabetes is a moderate risk factor for metabolic syndrome in the offspring. But some other perinatal risk factors of metabolic syndrome carry a bigger influence. The influence of genetic factors and maternal overweight may not be easily distinguished from the impact of fetal exposure to gestational diabetes.

CONCLUSION

It remains uncertain if the control of maternal glycemia alone may be effective and sufficient to prevent the metabolic syndrome in the adult-aged offspring.

Does frank diabetes in first-degree relatives of a pregnant woman affect the likelihood of her developing gestational diabetes mellitus or nongestational diabetes?

OBJECTIVE

We sought to examine the associations between patterns of family histories of diabetes and a history of gestational diabetes mellitus (hGDM).

STUDY DESIGN

Parous women participating in the National Health and Nutrition Examination Survey III (n=4566) were classified as having hGDM only, diagnosed diabetes, or neither. Family history of diabetes was categorized as: maternal only, paternal only, biparental, and sibling only. The covariate-adjusted prevalence and odds of having hGDM were estimated.

RESULTS

Compared to women without a family history of diabetes, women with a maternal (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.2-7.3), paternal (OR, 3.3; 95% CI, 1.1-10.2), or sibling (OR, 7.1; 95% CI, 1.6-30.9) history of diabetes had greater odds of hGDM, after adjustment for age and race/ethnicity.

CONCLUSION

Women with a sibling history of diabetes were more likely to have hGDM than women with other family history patterns.

Sibling and parental history in type 2 diabetes risk among ethnic Chinese: the Chin-Shan Community Cardiovascular Cohort Study

BACKGROUND

This study aims to compare various family history profiles as predictors of diabetes in a community-based prospective cohort because few prospective studies have examined the association of family history with diabetes risk in ethnic Chinese populations.

METHODS

Among 2960 participants free from baseline diabetes through the Chin-Shan Community Cardiovascular Cohort Study, there were 548 cases that developed diabetes after a median 9 years of follow-up.

RESULTS

After multivariate adjustment, sibling history was associated with diabetes [Relative risk (RR): 2.08, 95% confidence interval (CI): 1.42-3.06, P=0.0002]. Both maternal and paternal histories had similar effects (RR: 1.62, 95% CI: 1.04-2.51 for paternal history, RR: 1.36, 95% CI: 0.98-1.89 for maternal history). Obese participants with sibling history increased the risk of diabetes by 4.6-fold (RR: 4.61, 95% CI: 2.93-7.26), compared with those with neither obesity nor family history.

CONCLUSION

The findings support the hypothesis that sibling history is more important than parental history for diabetes risk.

Familial history of type 2 diabetes in patients from Southern Brazil and its influence on the clinical characteristics of this disease

OBJECTIVE

To investigate the presence of maternal and paternal history of type 2 diabetes mellitus (DM) in relatives of 644 type 2 diabetic patients from Southern Brazil, and also to evaluate its influence on the clinical characteristics of this disease.

PATIENTS AND METHODS

Familial history of type 2 DM was investigated by a questionnaire. The maternal and paternal history was investigated over two generations. Complete data sets on familial history were obtained from 396 patients.

RESULTS

In general, 76.6% of the patients reported at least one first-degree affected relative. Besides, 31.6% of the patients reported a maternal history of type 2 DM and 12.6% reported a paternal history. Patients with maternal and/or paternal history presented a lower age at type 2 DM diagnosis when compared to patients without familial history. In addition, patients with only paternal history presented a higher frequency of hypertension than patients with no familial history.

CONCLUSIONS

This study suggests that there is a significant maternal effect in the transmission of type 2 DM in Southern Brazil, and that most of the clinical characteristics of this disease do not differ between patients with or without familial history of type 2 DM.

Familial aggregation and excess maternal transmission of type 2 diabetes in Tunisia

AIM

To evaluate the degree of familial aggregation of type 2 diabetes mellitus in Tunisia and to investigate transmission patterns of the disease and their relationships with patients' clinical profiles.

METHODS

Family history of diabetes and clinical data were collected for 132 unrelated type 2 diabetic Tunisian patients. Diabetes status was recorded for first degree relatives (parents, siblings) and second degree relatives (aunts and uncles from both maternal and paternal sides). Information about family history of diabetes was gathered for a total of 1767 individuals.

RESULTS

Familial aggregation of type 2 diabetes was prominent and more important among first degree relatives than among second degree relatives (p = 0.01). Among studied subjects, 70% reported at least one relative with diabetes and 34% had at least one parent with diabetes. Diabetes was more frequent among mothers than fathers of probands (p = 0.03). This maternal effect extends to second degree relatives as diabetes was more common among maternal than paternal aunts and uncles (p = 0.01). There is no significant difference in clinical and metabolic profiles between patients according to transmission patterns of the disease.

CONCLUSION

These results suggest familial aggregation and excess maternal transmission of type 2 diabetes in the Tunisian studied population.

Familial aggregation of ischemic stroke in young women: the Stroke Prevention in Young Women Study

BACKGROUND AND PURPOSE

Stroke occurs infrequently in young adults. While a familial basis for older onset stroke is well established, the extent of familial clustering in young-onset stroke is unknown. To address this issue, we compared the frequency of stroke in relatives of stroke cases to that in relatives of controls across different ages and by stroke subtype.

METHODS

Through a population-based case-control study of stroke, we identified 487 women aged 15-49 years with ischemic stroke and 615 women without stroke matched by age and geographic region. Family history of stroke was collected for 5,749 relatives (parents and siblings) of case and control probands by standardized interview.

RESULTS

Strokes were reported in 149 relatives of case patients and 119 relatives of controls. Siblings of stroke case patients had more than four times the risk of stroke compared to siblings of controls (OR, 4.17; 95% CI, 1.9-8.8) and mothers of stroke case patients had twice the risk of stroke compared to mothers of control subjects (OR, 2.02; 95% CI, 1.4-3.0). The association between stroke in probands and family history of stroke was strongest among women aged 15-24 years (OR, 2.5; 95% CI, 0.4-15.1), and diminished with increasing proband age (OR, 1.6; 95% CI, 0.8-3.3 among women 25-34 years and OR, 1.5; 95% CI, 1.1-1.9 among women 35-49 years; P<0.0001 for trend).

CONCLUSIONS

We conclude that young-onset stroke aggregates in families and that the magnitude of aggregation increases with decreasing proband age.

Early growth and type 2 diabetes: evidence from the 1946 British birth cohort

AIMS/HYPOTHESIS

We assessed whether low birthweight or early adiposity rebound was more strongly associated with type 2 diabetes, and whether any effect of low birthweight or early adiposity rebound was explained by adult BMI, adult height, social class of subject or of his/her father, or maternal or paternal diabetes.

METHODS

Cox's proportional hazard models were used on data from the National Birth Cohort Study (the MRC National Survey of Health and Development), which was begun in 1946 and had self-reported physician-diagnosed diabetes with age at onset ranging from 31 to 53 years (n=78 cases, and n=47 cases in the multivariate analysis) as the outcome.

RESULTS

A U-shaped association between birthweight and type 2 diabetes rates was close to statistical significance (quadratic term p value=0.08). Younger age at adiposity rebound was associated with increased rates of type 2 diabetes (test for trend p=0.002), the association being robust to adjustment for each of sex, birthweight, weight at 2 years, father's social class, parental diabetes, and own social class. The effect of early adiposity rebound was very slightly reduced by adjustment for sex and adult height (p=0.003), but considerably reduced after adjustment for sex and adult BMI (test for trend p=0.1), and further reduced (p=0.4) after additional adjustment for birthweight, weight at 2 years, adult height, social class of subject and of his/her father, and parental diabetes.

CONCLUSIONS/INTERPRETATION

Early adiposity rebound was associated with an increased rate of type 2 diabetes independently of birthweight, but its effect was mostly through high adult BMI. Parental diabetes and possibly low weight at 2 years were also risks.

Longitudinal changes in risk variables of insulin resistance syndrome from childhood to young adulthood in offspring of parents with type 2 diabetes: the Bogalusa Heart Study

The occurrence of metabolic abnormalities related to insulin resistance syndrome in nondiabetic offspring of type 2 diabetic parents is known. However, information is lacking on the timing and the course of development of the components of this syndrome from childhood to adulthood in the offspring of parents with diabetes. This aspect was examined in a community-based cohort with (n = 303) and without (n = 1,136) a parental history of type 2 diabetes followed longitudinally since childhood (ages 4 to 17 years; mean follow-up period, 15 years) by repeated surveys. Offspring with parental diabetes versus those without such history had significantly excess generalized and truncal adiposity as measured by body mass index (BMI) and subscapular skinfold beginning in childhood, higher levels of fasting insulin and glucose and homeostasis model assessment index of insulin resistance (HOMA-IR) from adolescence, and higher levels of low-density lipoprotein (LDL) cholesterol and triglycerides and lower levels of high-density lipoprotein (HDL) cholesterol in adulthood. Many of these risk variables changed adversely at an increased rate in offspring of diabetic parents. In a multivariate analysis, parental diabetes was an independent predictor of longitudinal changes in adiposity, glucose, insulin, HOM-IR, systolic and diastolic blood pressure, and LDL cholesterol in the offspring, regardless of race and gender. As young adults, the offspring of diabetic parents had a higher prevalence of generalized (BMI > 30, 36% v 16%, P =.0001) and visceral (waist > 100 cm, 15% v 6%, P =.0001) obesity, hyperinsulinemia indicative of insulin resistance (insulin > 18 microU/mL, 15% v 8%, P =.0001), hyperglycemia (>or=110 mg/dL, 2% v 0.5%, P =.02), high LDL cholesterol (>or=160 mg/dL, 11% v 7%, P =.02), low HDL cholesterol (<40 mg/dL for males and <50 mg/dL for females, 40% v 31%, P =.004), high triglycerides (>or=150 mg/dL, 23% v 15%, P =.0001), and hypertension (>140/90 mm Hg, 11% v 6%, P =.004). Thus, the offspring of diabetic parents displayed excess body fatness beginning in childhood and accelerated progression of adverse risk profile characteristics of insulin resistance syndrome from childhood to young adulthood. These observations have important implications for early prevention and intervention.

Excess maternal transmission and familial aggregation of Type 2 diabetes in Sri Lanka

INTRODUCTION

An excess of maternal transmission of Type 2 diabetes mellitus has been reported in Europid populations, but not in South India.

METHOD

A questionnaire-based survey was carried out in 1000 (502 male) people with Type 2 diabetes to establish whether there is an excess of maternal transmission and familial aggregation in a Sri Lankan population.

RESULTS

Mean age of onset was 47+/-12 (+/-S.D.) years and duration of diabetes was 9+/-7 years. Thirty-seven percent reported parents with diabetes, 46.9% had no parents with diabetes, 16.1% did not know the diabetes status of at least one parent and there was no diabetes in the other. Of the probands, 59.4% had at least one affected relative. When both parents' diabetes status was known and only one was affected, diabetes was more common among mothers (n = 156) than fathers (n = 125) of probands (P < 0.001). A further 54 probands had both parents with diabetes. Mean age of onset and duration of the disease among probands with parental diabetes was 43.1+/-(11.1) and 9.6+/-(6.8). In the previous generation, 21.2% of maternal grandmothers and 17.3% of maternal grandfathers in the maternal diabetes group and 4.8% of maternal grandmothers and 17% of maternal grandfathers in the paternal diabetes group had diabetes. Diabetes in siblings and children was more common in those with mothers who had diabetes (53.8% and 4.5%) when compared with those in whom fathers had diabetes (42.4% and 1.6%) (P < 0.0001 and P < 0.01).

CONCLUSION

Familial aggregation and excess maternal transmission were observed in people with Type 2 diabetes in Sri Lanka.

Can inaccuracy of reported parental history of diabetes explain the maternal transmission hypothesis for diabetes?

BACKGROUND

The mode of inheritance of type 2 diabetes mellitus is still under discussion. Several studies have suggested an excess maternal transmission, however, more recent studies could not always confirm these findings.

METHODS

We investigated the frequency of a maternal and paternal history of diabetes among diabetic and non-diabetic subjects and assessed the association between diabetes and a parental history of diabetes among participants of the MONICA Augsburg study. As an extension to previous studies, unknown parental status was taken into account.

RESULTS

Of the 542 diabetic probands, 25.3% reported a positive maternal history of diabetes and 10.9% reported a positive paternal history of diabetes. Among the 12,209 non-diabetic participants a positive maternal history was also more common than a positive paternal history (12.5% versus 7.1%). Conversely, an unknown paternal status was more common than an unknown maternal status in both groups (diabetic subjects: 27.9% versus 16.8%, non-diabetic subjects: 16.8% versus 8.4%). Adjusted odds ratios (OR) for the association between a parental history of diabetes and diabetes status were similar for a positive maternal (OR = 2.9, 95% CI : 2.3-3.6) and paternal history (OR = 2.8, 95% CI : 2.1-3.8) and for an unknown maternal (OR = 1.3, 95% CI : 1.0-1.8) and paternal history (OR = 1.5, 95% CI : 1.2-1.9).

CONCLUSION

Our findings do not support a strong excess maternal transmission of diabetes. Epidemiological biases and failure to account for 'don't know' responses may in part explain the previously observed predominance of a maternal history of diabetes.

Insulin action and secretion in healthy Hispanic-Mexican first-degree relatives of subjects with type 2 diabetes

The aim of this study was to assess the early insulin secretion and insulin action of healthy non-diabetic Hispanic-Mexican subjects with and without family history of Type 2 diabetes (FHD). One hundred and twenty non-relative subjects were compared against 115 first-degree relatives of individuals with Type 2 diabetes. To assign the subjects to the correspondent group, the FHD was carefully ascertained by clinical examination of the participants' parents. Age and gender were matched criteria. Incomplete or unclear data about FHD, previous diagnosis of diabetes or chronic diseases were exclusion criteria. Subjects in both groups were required to have fasting glucose <6.1 mmol/l, and 2-h PG<7.7 mmol/l. Insulin action and secretion were estimated by HOMA (homeostasis model insulin analysis resistance index) and insulinogenic index, respectively. Logistic regression analysis showed an independent relationship between BMI and insulin resistance (HOMA score >5.0) (odds ratio, OR, 1.42, p=0.03), and between FHD and insulin resistance (OR 1.27, p=0.04). On the other hand, there was a strong and independent relationship between FHD and high early insulin secretion (insulinogenic index >0.72) (OR 1.64, p=0.01) but not between BMI and high early insulin secretion (OR 0.93, p=0.3). Healthy Mexican first-degree relatives of subjects with Type 2 diabetes show an independent relationship between FHD and both high early insulin response and decreased insulin action, whereas BMI was only related to insulin resistance.

Importance of family history in type 2 black South African diabetic patients

OBJECTIVE

To assess the family history of diabetes in type 2 black South African diabetics with emphasis on the parental phenotype.

DESIGN

Prospective case-control study in which family histories were obtained from patients.

SETTING

Diabetic clinic of a provincial teaching hospital in the Transkei region of South Africa.

SUBJECTS

A total of 1111 type 2 diabetics attending the diabetic clinic and 687 controls.

MAIN OUTCOME MEASURES

History of diabetes in parents, siblings, maternal and paternal grandparents, aunts, and uncles.

RESULTS

Altogether 27.3% of diabetic subjects had a family history of diabetes compared with 8.4% in the control group (p<0.01). Among the group with positive family history 82.6% reported only one diabetic family member, while 17.4% reported at least two relatives; 6.6% had a diabetic relative from both maternal and paternal sides, and 87.8% had first degree relative with diabetes. Among them there was a significant maternal aggregation with 64.7% of patients having a diabetic mother compared with 27% who had a diabetic father (p<0.01). No maternal effect was observed among the second and third degree relatives. Patients with positive family history had an earlier onset of diabetes than those without family history (p<0.01).

CONCLUSION

These data suggest that type 2 diabetes is heritable in black South African diabetics. It is also likely that maternal influences may play an important part.

Predominance of a maternal history of diabetes for patients with non-insulin-dependent diabetes mellitus. Implications for the intrauterine transmission of diabetes

In Europid populations, patients with non-insulin-dependent diabetes mellitus (NIDDM) are more than twice as likely to have a mother than a father with diabetes. We have examined this aspect in an Australian population. For this purpose records of 1,000 consecutive patients with NIDDM were reviewed. A history of diabetes was present in 193 mothers (19.3%) and in only 86 fathers (8.6%) (p < 0.0001). The predominance of maternal history of diabetes in patients with NIDDM is suggestive of a maternal transmission of this disorder. This metabolic tendency may develop due to an adverse intrauterine environment in women with undiagnosed gestational diabetes mellitus.

Non-insulin-dependent diabetes mellitus--a collision between thrifty genes and an affluent society

Non-insulin-dependent diabetes mellitus (NIDDM) is one of the most common non-communicable diseases in the world. It has become obvious that NIDDM is the result of a collision between thrifty genes and an affluent society. Genes predisposing to NIDDM might have been survival genes for our ancestors, helping them to store energy during long periods of starvation. When these genes are exposed to a sedentary lifestyle and high caloric intake typical to the Western world, they predispose to obesity and insulin resistance. NIDDM results when beta cells cannot compensate for insulin resistance by increasing insulin secretion. Therefore, at least two inherited defects can be expected in NIDDM, one causing obesity and insulin resistance and the other inability to increase insulin secretion. In reality there may be more inherited defects. It has become quite clear that diabetes cannot simply be divided into NIDDM and insulin-dependent diabetes mellitus (IDDM). The disease is more heterogeneous; unmasking this heterogeneity and identifying new subgroups of diabetes presents a challenge to modern molecular biology.

Genetic analysis of non-insulin dependent diabetes mellitus in the GK rat

Non-insulin dependent diabetes mellitus (NIDDM) is a major public health problem, but its aetiology remains poorly understood. We have performed a comprehensive study of the genetic basis of diabetes in the Goto-Kakizaki (GK) rat, the most widely used animal model of non-obese NIDDM. The genetic dissection of NIDDM using this model has allowed us to map three independent loci involved in the disease. In addition, we identify a major factor affecting body weight, but not glucose tolerance, on chromosome 7 and map a further 10 regions that are suggestive for linkage. We conclude that NIDDM is polygenic and fasting hyperglycaemia and postprandial hyperglycaemia clearly have distinct genetic bases.