Expanding the Phenotypic Spectrum of Nicotinamide Nucleotide Transhydrogenase (NNT) Mutations and using Whole Exome Sequencing to Discover Potential Disease Modifiers

Mutations in the NNT gene (nicotinamide nucleotide transhydrogenase), which is involved in NADPH generation in mitochondria, have recently been described in familial glucocorticoid deficiency. We report two patients, one with isolated glucocorticoid deficiency and the other with a combined glucocorticoid and mineralocorticoid deficiency. Through whole exome sequencing, both cases were found to carry two different NNT mutations, confirming previous results for these patients. Each patient also carries multiple heterozygous protein-altering mutations in other genes involved in steroid hormone biogenesis and regulation. The patient with a combined glucocorticoid and mineralocorticoid deficiency is a compound heterozygote for common missense variants in the ME3 gene (mitochondrial malic enzyme 3), the product of which also generates NADPH in mitochondria. Mutations in NNT are the likely proximal cause of the glucocorticoid deficiency in both patients, but genetic background effects may be important in modulating the specific phenotype of adrenal insufficiency.