Clinical Description
Diabetes mellitus. Permanent neonatal diabetes mellitus (PNDM) is characterized by the onset of hyperglycemia within the first six months of life, with a mean age at diagnosis of seven weeks (range: birth to age 26 weeks) [Gloyn et al 2004b]. Clinical manifestations at diagnosis include intrauterine growth restriction (IUGR; a reflection of insulin deficiency in utero), hyperglycemia, glycosuria, osmotic polyuria, severe dehydration, and poor weight gain.
The diabetes mellitus is associated with partial or complete insulin deficiency. Therapy with insulin corrects the hyperglycemia and results in dramatic catch-up growth. Many individuals with ABCC8- or KCNJ11-related PNDM have improved glycemic control with sulfonylureas alone or combined with insulin treatment. Long-term follow-up studies of infants diagnosed with ABCC8- or KCNJ11-related PNDM showed that most individuals had good glycemic control on sulfonylureas with HgA1c averaging 5.9%-6.0% and minimal hypoglycemia with an average follow-up time of five to ten years [Bowman et al 2018, Warncke et al 2022].
Reports of microvascular complications vary among cohorts, with 4%-19% of affected individuals reported to have microalbuminuria and 6% reported to have retinopathy. There was no strong evidence that treatment with sulfonylureas was less effective over time, but there was a trend that later initiation of sulfonylurea treatment was associated with the need for combined treatment with insulin.
Genotype-Phenotype Correlations
No genotype-phenotype correlations for EIF2AK3, GATA6, GCK, GLIS3, HNF1B, MNX1, NEUROD1, NKX2-2, PDX1, RFX6, SLC2A2, or SLC19A2 have been identified.
ABCC8. For neonatal diabetes caused by pathogenic variants in ABCC8, genotype-phenotype correlations are less distinct [Edghill et al 2010]. Children with neonatal diabetes associated with autosomal dominant ABCC8 pathogenic variants may have a parent with the same ABCC8 variant and type 2 diabetes, suggesting that the severity of the phenotype and age of onset of diabetes is variable among individuals with ABCC8 pathogenic variants [Babenko et al 2006].
INS. The relationship between genotype and phenotype is beginning to emerge for neonatal diabetes mellitus caused by pathogenic variants in INS. The diabetes mellitus in persons who are homozygous or compound heterozygous for pathogenic variants in INS can be permanent or transient. The variants c.-366_343del, c.3G>A, c.3G>T, c.184C>T, c.-370-?186+?del (a 646-bp deletion), and c.*59A>G appear to be associated with PNDM, whereas the variants c.-218A>C and c.-331C>A or c.-331C>G have been identified in persons with both PNDM and TNDM as well as persons with childhood-onset monogenic diabetes, also called type 1b diabetes mellitus [Støy et al 2010] due to features including absence of evidence of beta cell autoimmunity, low serum C peptide, and insulin dependency.
KCNJ11. Some KCNJ11 pathogenic variants are associated with TNDM; others are associated with PNDM; and two variants, p.Val252Ala and p.Arg201His, are associated with both disorders [Colombo et al 2005, Girard et al 2006]. Furthermore, functional studies have shown some overlap between the magnitude of the KATP channel currents in TNDM- and PNDM-associated pathogenic variants [Girard et al 2006, Ashcroft 2023].
The location of the KCNJ11 pathogenic variant can partially predict the severity of the disease, i.e., isolated diabetes mellitus, intermediate DEND (developmental delay, epilepsy, and neonatal diabetes mellitus) syndrome, DEND syndrome; however, there are some exceptions. Studies have evaluated reduction in KATP channel ATP sensitivity and its effect on phenotype. Pathogenic variants in residues that lie within the putative ATP binding site (Arg50, Ile192, Leu164, Arg201, Phe333) or are located at the interfaces between Kir6.2 subunits (Phe35, Cys42, and Gu332) or between Kir6.2 and SUR1 (Gly53) are associated with isolated diabetes mellitus. See Molecular Genetics.
The severity of PNDM along the spectrum of isolated diabetes mellitus, intermediate DEND syndrome, and DEND syndrome correlates with the genotype [Proks et al 2004]. KCNJ11 variants that cause additional neurologic features occur at codons for amino acid residues that lie at some distance from the ATP binding site (Gln52, Gly53, Val59, Cys166, and Ile296) [Hattersley & Ashcroft 2005, Ashcroft 2023].
Of 24 individuals with pathogenic variants at the arginine residue, Arg201, all but three had isolated PNDM.
The p.Val59Met variant is associated with intermediate DEND syndrome.
Improvement of the neurologic features of DEND syndrome with sulfonylurea treatment also appears to be genotype dependent: children with the variants p.Val59Met [
Støy et al 2008,
Mohamadi et al 2010] and p.Gly53Asp [
Koster et al 2008] have been shown to respond to sulfonylureas.
PTF1A. Biallelic null variants are associated with pancreatic and cerebellar agenesis. Biallelic pathogenic variants involving the downstream enhancer region are associated with isolated pancreatic agenesis.