MODY (maturity-onset diabetes of the young) comprises 14 distinct types, each caused by a mutation in a different gene that affects pancreatic beta-cell development or insulin secretion. The three most common types — HNF1A, GCK, and HNF4A — account for roughly 90 percent of diagnosed cases, and each has a different clinical phenotype and optimal treatment.
Overview of the 14 MODY Types
| MODY | Gene | Frequency | Hallmark Feature |
|---|---|---|---|
| MODY 1 | HNF4A | ~5 to 10% | Macrosomia and neonatal hypoglycemia |
| MODY 2 | GCK | ~30 to 50% | Mild stable fasting hyperglycemia |
| MODY 3 | HNF1A | ~50% | Glycosuria at low blood glucose |
| MODY 4 | PDX1 (IPF1) | <1% | Homozygous form — pancreatic agenesis |
| MODY 5 | HNF1B | ~5% | Renal cysts and diabetes (RCAD) |
| MODY 6 | NEUROD1 | Rare | Variable onset |
| MODY 7 | KLF11 | Rare | Variable presentation |
| MODY 8 | CEL | Rare | Exocrine pancreatic dysfunction |
| MODY 9 | PAX4 | Rare | Variable, often ketosis-prone |
| MODY 10 | INS | Rare | Insulin gene mutation |
| MODY 11 | BLK | Rare | Disputed pathogenicity |
| MODY 12 | ABCC8 | Rare | Sulfonylurea-responsive |
| MODY 13 | KCNJ11 | Rare | Sulfonylurea-responsive |
| MODY 14 | APPL1 | Very rare | Recently identified |
MODY 1 — HNF4A
- HNF4A encodes hepatocyte nuclear factor 4 alpha — a transcription factor regulating beta-cell function
- Onset typically in adolescence or young adulthood with progressive hyperglycemia
- Newborns of affected mothers often have macrosomia (large birth weight) and neonatal hypoglycemia from in-utero hyperinsulinemia
- Low HDL cholesterol and apolipoprotein levels may be present
- Responds to low-dose sulfonylureas — gliclazide is commonly used
- Insulin may be needed later as beta-cell function declines
MODY 2 — GCK
- GCK encodes glucokinase — the pancreatic beta-cell glucose sensor
- Heterozygous mutation raises the glucose set-point, producing mild stable fasting hyperglycemia from birth
- Fasting glucose typically 95 to 150 mg/dL, A1C 5.6 to 7.6 percent — rarely worsens with age
- Long-term complications are uncommon — patients do not need medication outside pregnancy
- OGTT often shows only a modest rise above baseline
- Pregnancy management depends on fetal genotype — if the fetus has inherited the variant, no maternal treatment is needed; if not, tighter maternal control prevents macrosomia
- Often discovered incidentally during routine bloodwork or pregnancy screening
MODY 3 — HNF1A
- Most common MODY type — roughly 50 percent of identified cases
- HNF1A is a transcription factor critical for beta-cell function
- Progressive hyperglycemia starting in adolescence or young adulthood
- Low renal glucose threshold — glycosuria appears at blood glucose levels around 130 to 140 mg/dL
- Very sensitive to low-dose sulfonylureas — patients on insulin can often switch
- Increased microvascular and cardiovascular risk if untreated
- OGTT shows an exaggerated post-load glucose rise compared with fasting
MODY 4 — PDX1 (IPF1)
- PDX1 encodes pancreatic and duodenal homeobox 1 — a master regulator of pancreatic development
- Heterozygous mutations cause MODY in young adults
- Homozygous mutations cause pancreatic agenesis with neonatal diabetes
- Very rare in heterozygous form
MODY 5 — HNF1B (RCAD Syndrome)
- HNF1B encodes a transcription factor involved in pancreatic and renal development
- Renal cysts and diabetes syndrome (RCAD) — renal cysts often precede diabetes
- Other features may include genitourinary anomalies, pancreatic hypoplasia, hyperuricemia, abnormal liver enzymes
- Often requires insulin — sulfonylureas less effective
- Needs multi-system follow-up — nephrology, endocrinology, sometimes urology
- Many cases arise from de novo deletions on chromosome 17 — family history may be absent
MODY 6 — NEUROD1
- NEUROD1 is a transcription factor important for beta-cell maturation
- Variable onset and severity
- Rare
MODY 7 to 14 — Rare Subtypes
- MODY 7 (KLF11), MODY 8 (CEL), MODY 9 (PAX4), MODY 10 (INS), MODY 11 (BLK) — all rare with variable phenotypes
- MODY 12 (ABCC8) and MODY 13 (KCNJ11) — encode subunits of the beta-cell potassium channel; these are sulfonylurea-responsive and overlap with neonatal diabetes
- MODY 14 (APPL1) — recently described, very rare
- BLK-MODY pathogenicity is disputed in current literature
Treatment by MODY Subtype
| Subtype | Preferred Treatment | Avoid |
|---|---|---|
| HNF1A-MODY (MODY 3) | Low-dose sulfonylurea (e.g., gliclazide) | High-dose insulin if SU effective |
| HNF4A-MODY (MODY 1) | Low-dose sulfonylurea | High-dose insulin if SU effective |
| GCK-MODY (MODY 2) | No medication (outside pregnancy) | Unnecessary insulin or sulfonylurea |
| HNF1B-MODY (MODY 5) | Insulin commonly required | Reliance on sulfonylureas alone |
| ABCC8 or KCNJ11-MODY | Sulfonylureas — often very effective | Insulin first-line when SU works |
| Other rare subtypes | Individualized — based on residual beta-cell function | Sweeping generalizations |
Differential Diagnostic Features
| Clue | Subtype Suggested |
|---|---|
| Mild fasting hyperglycemia stable from childhood | GCK-MODY |
| Macrosomia and neonatal hypoglycemia | HNF4A-MODY |
| Glycosuria at low blood glucose | HNF1A-MODY |
| Renal cysts plus diabetes | HNF1B-MODY |
| Exocrine pancreatic dysfunction | CEL-MODY (MODY 8) |
| Sulfonylurea hypersensitivity | HNF1A or HNF4A or ABCC8 or KCNJ11 |
| Diabetes diagnosed under 6 months | Consider neonatal diabetes |
Genetic Testing and Counseling
- Targeted next-generation sequencing (NGS) panels are now standard
- Family members should be offered cascade testing after a variant is identified
- Genetic counseling helps families understand inheritance and screening
- Many MODY mutations are pathogenic, but some variants are of uncertain significance (VUS) and require expert interpretation
Long-Term Outlook
Complication risk depends on the subtype. GCK-MODY carries the lowest long-term risk and typically requires no intervention beyond pregnancy management. HNF1A and HNF4A-MODY have similar microvascular and cardiovascular risk to other forms of diabetes when untreated, so tight glycemic control matters. HNF1B-MODY needs ongoing renal monitoring. See our guide on complications and related conditions for more.
Related Reading
For more on monogenic and atypical diabetes, see our companion guides on MODY foundations, LADA, neonatal diabetes, mitochondrial diabetes, and our prediabetes basics hub.
The Bottom Line
The 14 MODY types each have a distinct gene, clinical phenotype, and optimal treatment. HNF1A, GCK, and HNF4A account for roughly 90 percent of cases. Genetic testing identifies the specific subtype, and the result frequently changes management — some patients on insulin can switch to low-dose sulfonylureas, others can stop medication altogether, and a few need multi-system follow-up. If you have an unusual pattern of diabetes — diagnosed young, lean, antibody-negative, with strong family history — talk to your doctor or a genetic counselor about testing.
