Switching to Sulphonylureas in Children With iDEND Syndrome Caused by KCNJ11 Mutations Results in Improved Cerebellar Perfusion

OBJECTIVE

Activating mutations in the KCNJ11 gene, encoding the Kir6.2 subunit of the K_ATP channel, result in permanent neonatal diabetes mellitus. They also may cause neurologic symptoms such as mental retardation and motor problems (iDEND syndrome) and epilepsy (DEND syndrome). Sulphonylurea (SU) treatment is reported to alleviate both the neurologic symptoms and diabetes in such cases. The study aimed to establish the magnitude and functional basis of the effect of SUs on the neurologic phenotype in children with iDEND using neuroimaging before and after insulin replacement with glibenclamide.

RESEARCH DESIGN AND METHODS

To localize and quantify the effect of glibenclamide administration, we performed single-photon emission computed tomography in seven patients with different mutations in KCNJ11. In five patients, measurements before and after initiation of SU treatment were performed.

RESULTS

Significant changes in single-photon emission computed tomography signal intensity after transfer to SU therapy were restricted to the cerebellum, consistent with previous data showing high Kir6.2 expression in this brain region. Cerebellar perfusion improved for both left (P = 0.006) and right (P = 0.01) hemispheres, with the mean improvement being 26.7 ± 7.1% (n = 5). No patients showed deterioration of cerebellar perfusion on SU therapy. Electrophysiological studies revealed a good correlation between the magnitude of K_ATP channel dysfunction and the clinical phenotype; mutant channels with the greatest reduction in adenosine 5′-triphosphate inhibition were associated with the most severe neurologic symptoms.

CONCLUSIONS

We conclude it is likely that at least some of the beneficial effects of SU treatment on neurodevelopment in iDEND patients result from improved cerebellar perfusion.Approximately 50% of cases of permanent neonatal diabetes mellitus are caused by mutations in the genes encoding either the pore-forming (Kir6.2, KCNJ11) or regulatory (SUR1, ABCC8) subunits of the ATP-sensitive K⁺ (K_ATP) channel (1). In some patients with these mutations, neurologic symptoms such as mental retardation, impaired motor development, and hypotonia coexist with neonatal diabetes (iDEND syndrome); if epilepsy is also present, then the condition is called DEND syndrome (2). Previous studies have shown that it is possible to alleviate diabetes and some of the neurologic symptoms by substituting insulin therapy with orally ingested sulphonylurea (SU) drugs (3). In one patient, the improvement in neurologic function was associated with enhanced perfusion of the brain, particularly of the cerebellum, as measured by single-photon emission computed tomography (SPECT). To determine if this effect is common to patients treated with SU, we performed SPECT in patients with different mutations in KCNJ11 and varying clinical phenotypes.