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# Monogenic and gestational diabetes

- Mechanism

A few people have diabetes from a single gene change. Diabetes during pregnancy affects both the mother and the baby.

Updated Nov 12, 2026

## Key points

- MODY: autosomal dominant, young onset, not obese, no autoantibodies; GCK (mild stable hyperglycaemia), HNF1A and HNF4A (sulfonylurea-sensitive), HNF1B (with kidney cysts).
- Permanent neonatal diabetes: activating KCNJ11 or ABCC8 mutations keep KATP channels open; many switch from insulin to sulfonylureas.
- Mitochondrial diabetes: m.3243A>G, maternal inheritance, with deafness.
- Insulin receptor mutations: type A insulin resistance, Donohue syndrome (leprechaunism) and Rabson-Mendenhall syndrome, with acanthosis nigricans.
- Lipodystrophy: loss of fat stores leads to fat in liver and muscle and severe insulin resistance.
- Pregnancy: early hyperglycaemia causes malformations (heart, neural tube, caudal regression); later hyperglycaemia causes macrosomia and neonatal hypoglycaemia.

## What it is

Monogenic diabetes is a small but important group caused by single-gene defects in beta-cell function or insulin action. Recognising it changes treatment: some forms respond to sulfonylureas instead of insulin, and some need no treatment. Diabetes in pregnancy, whether pre-existing or gestational, exposes the fetus to high glucose, which causes overgrowth and, when present early, malformations.

## Step by step

- Maternal glucose crosses the placenta; insulin does not.
- The fetal pancreas responds with beta-cell hyperplasia and hyperinsulinaemia.
- Fetal insulin acts as a growth factor: macrosomia, organomegaly, delayed lung maturation.
- At birth the glucose supply stops but fetal insulin stays high: neonatal hypoglycaemia.
- Hyperglycaemia during organogenesis disturbs development: cardiac, neural tube and caudal defects.

## Single-gene diabetes to know

| Form | Gene | Defect | Clue |
| --- | --- | --- | --- |
| MODY (glucokinase) | GCK | Glucose sensor set too high | Mild lifelong fasting hyperglycaemia, rarely needs treatment |
| MODY (transcription factors) | HNF1A, HNF4A | Less insulin secretion | Responds well to sulfonylureas |
| MODY with kidney disease | HNF1B | Pancreas and kidney development | Renal cysts, genital anomalies |
| [Neonatal diabetes](https://durgical.com/en/conditions/neonatal-hypoglycaemia/) | KCNJ11, ABCC8, INS | KATP channel stuck open or insulin gene defect | Diabetes before six months of age |
| Mitochondrial | m.3243A>G | Beta-cell energy failure | Maternal inheritance, deafness |
| [Insulin receptor defects](https://durgical.com/en/conditions/acanthosis-nigricans/) | INSR | No insulin signal | Severe resistance, acanthosis nigricans, hyperandrogenism |

## Clinical notes

- Suspect MODY in a young, non-obese patient with a strong dominant family history and no autoantibodies.
- Gestational diabetes predicts later type 2 diabetes in the mother.

## Memory aid

MODY runs down the family tree like a dominant ribbon; neonatal diabetes is a door (KATP) stuck open, closed again by a pill.

## Test yourself

Think of the answer, then tap the question to see it.

## Why do many babies with KCNJ11 neonatal diabetes respond to sulfonylureas?

Sulfonylureas close the overactive KATP channels directly, restoring depolarisation and insulin release.

## Why are infants of diabetic mothers hypoglycaemic after birth?

Their beta cells are hyperplastic from fetal hyperglycaemia; insulin stays high when maternal glucose supply stops.

## Which MODY form usually needs no treatment?

Glucokinase (GCK) MODY, with mild stable fasting hyperglycaemia.

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## Elsewhere in DurgiPedia

- [Maternal diabetes and obesity as teratogens](https://durgical.com/en/embryology/maternal-diabetes-and-obesity-as-teratogens/)
- [Mendelian inheritance: autosomal dominant, recessive and X-linked](https://durgical.com/en/general-pathology/mendelian-inheritance-autosomal-dominant-recessive-and-x-linked/)
- [Nonclassic inheritance: repeat expansions, mitochondrial genes, imprinting, mosaicism](https://durgical.com/en/general-pathology/nonclassic-inheritance-repeat-expansions-mitochondrial-genes-imprinting-mosaicis/)

## Connections

## Related 4

- [Diabetes mellitus: diagnosis and classification](https://durgical.com/en/general-pathology/diabetes-mellitus-diagnosis-and-classification/)
- [Type 2 diabetes](https://durgical.com/en/general-pathology/type-2-diabetes/)
- [Mendelian inheritance: autosomal dominant, recessive and X-linked](https://durgical.com/en/general-pathology/mendelian-inheritance-autosomal-dominant-recessive-and-x-linked/)
- [Nonclassic inheritance: repeat expansions, mitochondrial genes, imprinting, mosaicism](https://durgical.com/en/general-pathology/nonclassic-inheritance-repeat-expansions-mitochondrial-genes-imprinting-mosaicis/)

## Related conditions 4

- [Gestational diabetes mellitus](https://durgical.com/en/conditions/gestational-diabetes-mellitus/)
- [Neonatal hypoglycaemia (including infant of a diabetic mother)](https://durgical.com/en/conditions/neonatal-hypoglycaemia/)
- [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/)
- [Type 1 diabetes mellitus](https://durgical.com/en/conditions/type-1-diabetes-mellitus/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Maturity-onset diabetes of the young](https://medlineplus.gov/genetics/condition/maturity-onset-diabetes-of-the-young/) (MedlinePlus, US National Library of Medicine, 2025); [Permanent neonatal diabetes mellitus](https://medlineplus.gov/genetics/condition/permanent-neonatal-diabetes-mellitus/) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/monogenic-and-gestational-diabetes/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/monogenic-and-gestational-diabetes/