High insulinlike growth factor I is associated with cognitive decline in Huntington disease

# {#article-title-2} To the Editor: Saleh et al.1 reported an association between higher plasma insulin-like growth factor (IGF)-1 levels and a greater degree of cognitive deterioration in patients with Huntington disease (HD). This is remarkable because IGF-1 has neuroprotective properties and has been shown to slow cognitive decline in other populations.2 The authors speculated that IGF-1 resistance might underlie cognitive decline in HD. Although this is an interesting hypothesis, recent advances suggest at least 2 alternative explanations. First, we recently found that the total diurnal production of growth hormone (GH) increases with disease severity in patients with HD.3 Moreover, GH secretion was more irregular in patients with greater motor and functional disability.3 These findings indicate progressive pathology of structures involved in the regulation of GH secretion—particularly the GH-releasing hormone …