We investigated the severely depleted oligodendrocyte cluster Oligo Birch, and found that this expressed OPALIN, previously described as a marker of newly formed oligodendrocytes [43] and myelin-forming oligodendrocytes in rodents [44], as well as the cytoskeletal component FMN1. The expression of these two genes in this cluster suggests Oligo Birch as an actively myelinating population of oligodendrocytes, and the loss of this cluster of myelin forming oligodendrocytes is consistent with the myelin changes seen in HD and preclinical HD models [6, 20, 45]. The gene discussed is FMN1; the disease is Huntington disease.