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

BACKGROUND

Mutations in the KCNJ11 gene, which encodes the Kir6.2 subunit of the β-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 ≈ 20% 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We identified from the literature, and our unpublished series, KCNJ11 mutations that affected residues harbouring various amino acid substitutions (AAS) causing differences in diabetic or neurological status.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 (P=0.013) or diabetes without neurological features (P=0.016) 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.