Correcting genetic diseases by base- and prime editing

We aim to tackle two rare neurological diseases that are caused by mutations in voltage-gated sodium channels by genome editing. Dravet Syndrome (DS), which is a disorder of the central nervous system (CNS), and Congenital Insensitivity to Pain (CIP), which is a disorder of the peripheral nervous system. DS, also known as severe myoclonic epilepsy of infancy (SMEI), is a severe form of epilepsy with an early onset during childhood. It is predominantly caused by heterozygous loss-of-function (LOF) mutations in the voltage-gated sodium channel gene SCN1A, leading to neuronal hyperexcitability. Current treatment is based on drugs that enhance neuronal inhibition (e.g. valproate), but the reduction in frequency of epileptic seizures and overall prognosis remains largely unsatisfactory. A total of over 400 pathogenic single nucleotide variants are listed on ClinVar for SCN1A, of which more than 200 account for DS. The vast majority of those variants are in principle targetable by prime editing, and approximately 100 are transition mutations that are also targetable by base editing.

CIP is genetically and clinically heterogeneous, caused by mutations in several different genes. Most frequently, the disease is caused by homozygous loss of function mutations in the SCN9A gene, which has been reported to result in the CIP with an anosmia phenotype. SCN9A encodes for the Nav1.7 sodium channel and is predominantly expressed in the peripheral nervous system (PNS), particularly in the dorsal root ganglia (DRG) and sympathetic ganglia. Approximately 30 mutations in SCN9A have been associated with CIP, and most of these are nonsense mutations causing truncated Nav1.7. They can be all theoretically corrected by prime editing, and half of them are transition point mutations that could also be corrected by base editing.