Sex-dependent effects of chromogranin B P413L allelic variant as disease modifier in amyotrophic lateral sclerosis

Recent genetic studies yielded conflicting results regarding a role for the variant chromogranin B (CHGB)(P413L) allele as a disease modifier in ALS. Moreover, potential deleterious effects of the CHGB(P413L) variant in ALS pathology have not been investigated. Here we report that in transfected cultured cells, the variant CHGB(L413) protein exhibited aberrant properties including mislocalization, failure to interact with mutant superoxide dismutase 1 (SOD1) and defective secretion. The CHGB(L413) transgene in SOD1(G37R) mice precipitated disease onset and pathological changes related to misfolded SOD1 specifically in female mice. However, the CHGB(L413) variant also slowed down disease progression in SOD1(G37R) mice, which is in line with a very slow disease progression that we report for a Swedish woman with ALS who is carrier of two mutant SOD1(D90A) alleles and two variant CHGB(P413L) and CHGB(R458Q) alleles. In contrast, overexpression of the common CHGB(P413) allele in SOD1(G37R) mice did not affect disease onset but significantly accelerated disease progression and pathological changes. As in transgenic mice, the CHGB(P413L) allele conferred an earlier ALS disease onset in women of Japanese and French Canadian origins with less effect in men. Evidence is presented that the sex-dependent effects of CHGB(L413) allelic variant in ALS may arise from enhanced neuronal expression of CHGB in females because of a sex-determining region Y element in the gene promoter. Thus, our results suggest that CHGB variants may act as modifiers of onset and progression in some ALS populations and especially in females because of higher expression levels compared to males.