Heterozygosity for Neuronal Ceroid Lipofuscinosis predisposes to Bipolar Disorder

Objective: Bipolar Disorder (BD) is an heritable chronic mental disorder causing psychosocial impairment, affecting patients with depressive/manic episodes. The familial transmission of BD does not follow any of the simple Mendelian patterns of inheritance. The aim of this study is to describe a new large family with twelve affected BD members: WES was performed in eight of them, three of which were diagnosed for BD, and one was reported as a "borderline" individual. Material and methods: WES data allowed us to select variants in common between the affected subjects, once including and once excluding a "borderline" subject with moderate anxiety and traits of obsessive-compulsive disorder. Results: Results were in favor of new predisposing BD genes, electing a heterozygous missense variant in CLN6 resulting in a "borderline" phenotype that if combined with a heterozygous missense variant in ZNF92 is responsible for the more severe BD phenotype. Both rare missense changes are predicted to disrupt the protein function. Conclusions: Loss of both alleles in CLN6 causes Neuronal Ceroid Lipofuscinosis, a severe progressive neurological disorder of childhood. Our results indicate that heterozygous CLN6 carriers, previously reported as healthy, may be susceptible to bipolar disorder late in life if associated with additional variants in ZNF92.