Wolfram syndrome is a rare disease characterized by diabetes, neurodegeneration, loss of vision, and audition. We recently found, in a young sample of participants (mean age 15 years), that Wolfram syndrome was associated with impairment in smell identification with normal smell sensitivity and whole-mouth taste function. However, these senses were assessed separately, and it is unknown whether smell-taste interactions are altered in Wolfram syndrome, which was the focus of this study. Participants with Wolfram syndrome (n = 36; 18.2 ± 6.8 years) and sex-age-equivalent healthy controls (n = 34) were assessed with a battery of sensory tests. Using sip-and-spit methods, participants tasted solutions containing gustatory and olfactory stimuli (sucrose with strawberry extract, citric acid with lemon extract, sodium chloride in vegetable broth, and coffee) with and without nose clips, and rated perceived taste and retronasal smell intensities using the generalized Labeled Magnitude Scale. Participants also completed n-butanol detection thresholds and the University of Pennsylvania Smell Identification Test (UPSIT). Retronasal smell increased taste intensity of sucrose, sodium chloride, and coffee solutions similarly in both groups (P values <0.03). Compared with the control group, participants in the Wolfram group had lower UPSIT scores and reduced smell sensitivity, retronasal intensity, and saltiness (P values <0.03), but rated other taste intensities similarly when wearing the nose clip. Despite impairments in orthonasal smell identification, odor-induced taste enhancement was preserved in participants with Wolfram syndrome who still had some peripheral olfactory function. This finding suggests that odor-induced taste enhancement may be preserved in the presence of reduced olfactory intensity.

Diabetes mellitus (DM), one of the most prevalent metabolic diseases in the world population, is associated with a number of comorbid conditions including obesity, pancreatic endocrine changes, and renal and cardio-cerebrovascular alterations, coupled with peripheral neuropathy and neurodegenerative disease, some of these disorders are bundled into metabolic syndrome. Type 1 DM (T1DM) is an autoimmune disease that destroys the insulin-secreting islet cells. Type 2 DM (T2DM) is diabetes that is associated with an imbalance in the glucagon/insulin homeostasis that leads to the formation of amyloid deposits in the brain, pancreatic islet cells, and possibly in the kidney glomerulus. There are several layers of molecular pathologic alterations that contribute to the DM metabolic pathophysiology and its associated neuropathic manifestations. In this review, we describe the general signature metabolic features of DM and the cross-talk with neurodegeneration. We will assess the underlying molecular key players associated with DM-induced neuropathic disorders that are associated with both T1DM and T2DM. In this context, we will highlight the role of tau and amyloid protein deposits in the brain as well in the pancreatic islet cells, and possibly in the kidney glomerulus. Furthermore, we will discuss the central role of mitochondria, oxidative stress, and the unfolded protein response in mediating the DM-associated neuropathic degeneration. This study will elucidate the relationship between DM and neurodegeneration which may account for the evolution of other neurodegenerative diseases, particularly Alzheimer's disease and Parkinson's disease as discussed later.

Diabetes mellitus (DM) is one of the most common diseases in the world population, associated with obesity, pancreatic endocrine changes, cardiovascular disease, renal glomerular disease, cerebrovascular disease, peripheral neuropathy, neurodegenerative disease, retinal disease, sleep apnea, some of which are bundled into the metabolic syndrome. The main characteristic of this disease is hyperglycemia, and often with albuminuria. Nevertheless, the classic features, with ketoacidosis in the extreme, are only a first layer of description of this condition. The description of the islet cells of the endocrine pancreas was first described by Opie, and the discovery of insulin by tying off the exocrine pancreatic ducts followed. We later find that the β-cells secrete insulin and glucagon, which synchronously stimulate or suppress glycogenolysis, and that insulin is essential for glucose intake into the cell. There are yet two other layers for our understanding of diabetes and the effects of its dysfunction, which is the basis for understanding the system-wide expression of the disease. We describe the molecular basis for the central nervous system neuropathic diseases that are associated with both Type 1 DM (T1DM) and Type 2 DM (T2DM), but more so with T2DM. T2DM is an autoimmune disease that destroys the insulin secreting islet cells. T2DM is the diabetes that is associated with an imbalance in the glucagon/insulin homeostasis that leads to the formation of amyloid deposits in the brain, pancreatic islet cells, and possibly the kidney glomerulus.