Synopsis
Recognise monogenic diabetes phenotypes, select NHS genomic testing appropriately, and translate a confirmed molecular diagnosis into safe person- and family-specific care.
- Monogenic diabetes results from a single-gene disorder and should be suspected when the phenotype does not fit common type 1 or type 2 mechanisms.
- Clues include diagnosis young in life, diabetes in successive generations, negative autoantibodies, persistent endogenous insulin secretion and gene-specific extra-pancreatic features.
- GCK-related hyperglycaemia is usually lifelong, mild and stable, often with fasting glucose around 5.5–8 mmol/L; treatment is generally unnecessary outside specialist pregnancy decisions.
- HNF1A- and HNF4A-related diabetes commonly progresses and can be highly sensitive to low-dose sulfonylureas, so molecular confirmation may allow specialist-supervised transfer from insulin.
- HNF1B disease often combines diabetes with renal developmental abnormalities, genital tract anomalies, hypomagnesaemia, abnormal liver tests or pancreatic exocrine dysfunction and may need insulin.
- Diabetes diagnosed before six months is unlikely to be autoimmune type 1 and warrants urgent neonatal-diabetes genomic testing because some channel variants respond to specialist high-dose sulfonylurea therapy.
- Use the current NHS National Genomic Test Directory and regional genomic laboratory eligibility route; a variant of uncertain significance is not a treatment instruction.
- A confirmed pathogenic familial variant enables targeted testing and counselling for relatives, with consent, reproductive implications and privacy handled explicitly.
Investigation priorities
Define inheritance, age at onset, treatment, neonatal history and extra-pancreatic features before genomic selection.
Management branches
Diabetes age, family pattern or syndromic features do not fit routine type 1 or type 2 classification.
- Construct a three-generation pedigree and record exact diagnosis ages, therapies, birth histories, renal, hearing, neurological and pregnancy features.
- Review autoantibodies, paired C-peptide, HbA1c trajectory and current insulin safety, treating any active deficiency without waiting for genomic results.
- Discuss the case with a monogenic diabetes or genomic service and apply the current NHS test-directory eligibility and consent pathway to select the right test.
Key medicines
Sulfonylurea for HNF1A or HNF4A diabetesBegin only after specialist confirmation, using a lower-than-usual oral starting dose and slow titration against glucose because marked sensitivity is common; insulin transfer requires close supervision.Hypoglycaemia can occur at small doses, particularly with missed meals, exercise or renal impairment. Do not extrapolate response to GCK, HNF1B or an unconfirmed genetic variant.
InsulinUse an individual basal-bolus, pump or neonatal specialist regimen according to current secretion, age, nutrition, pregnancy and glucose patterns; any reduction after genetic diagnosis must be supervised.Abrupt withdrawal risks severe hyperglycaemia or ketosis. Teach hypoglycaemia, ketone and sick-day care, and maintain backup treatment during any gene-directed transition.