In a patient with permanent neonatal diabetes mellitus (PNDM2; 618856), Gloyn et al. (2004) identified a heterozygous arg201-to-cys (R201C) mutation in the Kir6.2 gene. The patient was diagnosed at 4 weeks of age and had no additional neurologic or dysmorphic features. The arg201 residue lies close to the ATP-binding site and was implicated in ATP sensitivity (Ribalet et al., 2003).
Proks et al. (2004) stated that the 2 mutations in residue arg201, R201H (600937.0002) and R201C, which lie in the ATP-binding site of Kir6.2, cause milder PNDM disease without neurologic features; however, Massa et al. (2005) identified the R201C mutation in a patient with PNDM who also had muscle weakness and delayed motor development.
Gloyn et al. (2004) described a family in which 2 affected paternal half-sibs were heterozygous for the R201C mutation. Direct sequencing of leukocyte DNA showed that their clinically unaffected mothers and father were genotypically normal. Quantitative real-time PCR analysis of the father's leukocyte DNA detected no trace of mutant DNA. These results were consistent with the father being mosaic for the mutation, which was restricted to his germline. Gloyn et al. (2004) concluded that the high percentage of permanent neonatal diabetes cases due to de novo KCNJ11 mutations (Gloyn et al., 2004) suggests that germline mosaicism may be common.
