Amino acid properties may be useful in predicting clinical outcome in patients with Kir6.2 neonatal diabetes

Abstract

Background: Mutations in the KCNJ11 gene, which encodes the Kir6.2 subunit of the b-cell K ATP channel, are a common cause of neonatal diabetes. The diabetes may be permanent neonatal diabetes mellitus (PNDM) or transient neonatal diabetes mellitus (TNDM), and in w20% of patients, neurological features are observed. A correlation between the position of the mutation in the protein and the clinical phenotype has previously been described; however, recently, this association has become less distinct with different mutations at the same residues now reported in patients with different diabetic and/or neurological phenotypes. Methods: We identified from the literature, and our unpublished series, KCNJ11 mutations that affected residues harbouring various amino acid substitutions (AAS) causing differences in diabetic or neurological status. Using the Grantham amino acid scoring system, we investigated whether the difference in properties between the wild-type and the different AAS at the same residue could predict phenotypic severity. Results: Pair-wise analysis demonstrated higher Grantham scores for mutations causing PNDM or diabetes with neurological features when compared with mutations affecting the same residue that causes TNDM (PZ0.013) or diabetes without neurological features (PZ0.016) respectively. In just five of the 25 pair-wise analyses, a lower Grantham score was observed for the more severe phenotype. In each case, the wild-type residue was glycine, the simplest amino acid. Conclusion: This study demonstrates the importance of the specific AAS in determining phenotype and highlights the potential utility of the Grantham score for predicting phenotypic severity for novel KCNJ11 mutations affecting previously mutated residues.

Genetic and clinical features of neonatal and early onset diabetes mellitus in a tertiary center cohort in Brazil

“…Although this variant has not been described, there is a description of another variant in the same residue classified as pathogenic. 43 ABCC8 variants account for 11% of NDM cases in nonconsanguineous families, 24 In the present study, two male patients, P1 and P6, had homozygosis variants in FOXP3. The prevalence of IPEX syndrome is less than 1:1000000.…”

“…One novel variant was identified and classified as likely pathogenic (c.1000G > A/ p.Glv334Ser) in a patient (P21) with typical phenotype and good response to sulfonylurea. Although this variant has not been described, there is a description of another variant in the same residue classified as pathogenic 43 …”