Paraneoplastic cerebellar degeneration (PCD), characterized by progressive Purkinje neurone degeneration following paraneoplastic Yo antibody internalization and binding to cerebellar degeneration-related protein CDR2 and CDR2L, has been linked to intracellular calcium homeostasis imbalance due to calbindin D<sub>28k</sub> malfunction.
Neoplastic expression of Cdr2 in ovary and breast tumors triggers an autoimmune response that suppresses tumor growth by developing tumor immunity, but culminates in cerebellar degeneration when Cdr2-specific immune cells recognize neuronal Cdr2.
In spite of the generation of anti-Purkinje cell antibodies and PCD17-specific CTLs in vivo, neither clinical nor pathological changes consistent with significant cerebellar degeneration have been detected.
In order to address the possibility of further X chromosomal or autosomal genetic factors in RTT, we evaluated six candidate genes for RTT selected on clinical, pathological, and genetic grounds: UBE1 (human ubiquitin activating enzyme E1, located in chromosome Xp11.23), UBE2I (ubiquitin conjugating enzyme E2I, homologous to yeast UBC9, chromosome 16p13.3), GdX (ubiquitin-like protein, chromosome Xq28), SOX3 (SRY related HMG box gene 3, chromosome Xq26-q27), GABRA3 (gamma-aminobutyric acid type A receptor alpha3 subunit, chromosome Xq28), and CDR2 (cerebellar degeneration related autoantigen 2, chromosome 16p12-p13.1).