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Neonatal Diabetes genetics

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Neonatal Diabetes genetics

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"neonatal diabetes" AND genetics

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ISPAD 2022 monogenic diabetes neonatal diabetes genetic testing KCNJ11 ABCC8 6 months

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https://pmc.ncbi.nlm.nih.gov/articles/PMC10107883

Neonatal diabetes mellitus: genetics

Neonatal diabetes mellitus (NDM) is diabetes presenting before 6 months of age. It is usually monogenic, not autoimmune type 1 diabetes. All infants diagnosed before 6 months should receive urgent molecular genetic testing because the result can change treatment, identify associated malformations or neurologic disease, and guide family counseling. ISPAD guidance reports a molecular diagnosis in over 80% of these infants. Harrison's Principles of Internal Medicine, 22e, p. 3246.

Two clinical-genetic groups

GroupCourseMain genetic causes
Transient NDM (TNDM)Hyperglycemia develops in the neonatal period, usually remits within weeks to months, but diabetes may recur later, commonly in adolescence/adulthood6q24 imprinting abnormalities most common; also ABCC8, KCNJ11, less often INS, HNF1B
Permanent NDM (PNDM)Diabetes persists and requires long-term treatmentKCNJ11, ABCC8, INS are common; also pancreatic-development and syndromic genes

Major genetic causes

1. 6q24-related transient neonatal diabetes

This is the commonest cause of TNDM, accounting for about two-thirds of cases.
  • Overexpression of imprinted genes at chromosome 6q24, principally PLAGL1 and HYMAI.
  • Mechanisms:
    • Paternal uniparental disomy of chromosome 6
    • Paternal duplication of 6q24
    • Loss of maternal methylation at the 6q24 differentially methylated region
  • Typical phenotype:
    • Marked intrauterine growth restriction
    • Diabetes soon after birth
    • Remission, often by 12-18 months
    • Risk of later relapse
    • Sometimes macroglossia or umbilical hernia
Testing point: a sequencing-only panel can miss this diagnosis. Testing must include 6q24 methylation analysis and copy-number/UPD assessment. ISPAD monogenic diabetes guideline

2. KATP-channel diabetes: KCNJ11 and ABCC8

These genes encode the two subunits of the pancreatic beta-cell ATP-sensitive potassium channel:
  • KCNJ11 encodes Kir6.2
  • ABCC8 encodes SUR1
Normally, a rise in ATP after glucose metabolism closes the KATP channel, depolarizes the beta cell, opens calcium channels, and triggers insulin release. Activating variants keep the channel inappropriately open, so insulin secretion is suppressed.
  • May cause permanent or transient NDM.
  • Often de novo dominant variants, although inheritance varies.
  • KCNJ11 can be associated with developmental delay and epilepsy, particularly severe variants causing DEND syndrome: developmental delay, epilepsy, neonatal diabetes.
  • ABCC8 can also cause neurologic features, but they are generally less frequent/severe.
Pharmacogenetic importance: many patients with activating KCNJ11 or ABCC8 variants can transition from insulin to high-dose oral sulfonylurea, usually glibenclamide/glyburide, under specialist supervision. Earlier treatment may offer better neurologic benefit. ISPAD recommendations

3. INS mutations

Variants in the insulin gene may impair insulin synthesis, folding, or beta-cell survival.
  • A common cause of isolated PNDM after KATP-channel causes.
  • Usually causes insulin-deficient diabetes without major extrapancreatic abnormalities.
  • Can be dominant or recessive depending on the variant.
  • Treatment is generally insulin.

4. Genes causing pancreatic agenesis/hypoplasia

Consider these when neonatal diabetes is accompanied by exocrine pancreatic insufficiency, steatorrhea, or absent/small pancreas on imaging.
GeneCharacteristic association
GATA6Pancreatic agenesis/hypoplasia, congenital heart defects, sometimes biliary abnormalities
PDX1Pancreatic agenesis, exocrine pancreatic insufficiency
PTF1APancreatic agenesis plus cerebellar hypoplasia/aplasia
RFX6Mitchell-Riley syndrome: neonatal diabetes, intestinal atresia, biliary abnormalities
GATA4, MNX1, NKX2-2, NEUROD1Variable pancreatic developmental or neurologic syndromes

5. Syndromic permanent neonatal diabetes

GeneSyndrome / clinical clue
EIF2AK3Wolcott-Rallison syndrome: epiphyseal dysplasia, liver dysfunction/failure
FOXP3IPEX: enteropathy, eczema, autoimmunity in a male infant
GLIS3Congenital hypothyroidism, congenital glaucoma, renal disease
SLC19A2Thiamine-responsive megaloblastic anemia syndrome with deafness
SLC2A2Fanconi-Bickel syndrome: hepatomegaly, renal Fanconi syndrome
WFS1Wolfram-spectrum disease in selected cases
IER3IP1Microcephaly, epilepsy, diabetes syndrome
NEUROD1Neurodevelopmental abnormalities, sometimes sensorineural deafness

Inheritance and recurrence counseling

Inheritance depends on the molecular diagnosis:
  • De novo autosomal dominant: common in KCNJ11, ABCC8, and INS. If a parent carries the variant, each pregnancy has a 50% risk.
  • Autosomal recessive: common for several syndromic or pancreatic-development causes, such as EIF2AK3, GCK, PDX1, PTF1A, GLIS3, RFX6, and SLC19A2. If both parents are carriers, recurrence risk is 25% per pregnancy.
  • 6q24 imprinting disorders: recurrence depends on the exact mechanism. Paternal duplication and inherited methylation defects can carry substantial recurrence risk, whereas paternal UPD6 is often sporadic.
Gene-specific counseling is therefore necessary after confirming the molecular result. GeneReviews overview

Practical genetic work-up

For diabetes diagnosed before 6 months:
  1. Confirm persistent hyperglycemia and insulin deficiency.
  2. Send an urgent comprehensive NDM panel, including at minimum:
    • KCNJ11, ABCC8, INS
    • pancreatic-development genes
    • syndromic NDM genes
  3. Ensure testing includes:
    • sequencing and deletion/duplication analysis
    • 6q24 methylation testing
    • testing for paternal UPD6 where appropriate
  4. Assess phenotype-directed clues:
    • growth restriction and remitting diabetes: 6q24
    • developmental delay or seizures: KCNJ11/ABCC8, IER3IP1 and others
    • skeletal/liver disease: EIF2AK3
    • exocrine pancreatic failure: GATA6, PDX1, PTF1A, RFX6
    • diarrhea, eczema, autoimmunity in a boy: FOXP3
For onset at 6-12 months, genetic testing is still appropriate when islet autoantibodies are negative or clinical features suggest monogenic diabetes. ISPAD guideline
Exam takeaway:
6q24 = transient NDM; KCNJ11/ABCC8 = KATP-channel NDM and sulfonylurea-responsive; INS = isolated permanent NDM; EIF2AK3 = Wolcott-Rallison; GATA6/PDX1/PTF1A = pancreatic agenesis syndromes.
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