Genomic editing as a therapeutic approach to congenital adrenal hyperplasia

Abstract

Genome editing technology has reached a critical point where potentially curative treatments for a range of monogenic disorders are within reach. Monogenic adrenal disorders are underrepresented in gene therapy research, despite congenital adrenal hyperplasia (CAH) caused by 21 hydroxylase deficiency occurring in approximately 1 in 15000 live births. Current management for CAH involves corticosteroid treatment at pituitary axis-suppressing doses. Fluctuation from under- to over-treatment is common and expected, and results in adverse outcomes including adrenal crisis, virilisation of female patients (hirsutism, clitoromegaly, disordered menstruation), precocious puberty, short stature, hypertension, cushingoid side effects and impacts on mental health.

Adeno-associated virus (AAV) is one of the most promising gene therapy vectors available. However, a limitation of this vector is that it persists predominantly as an episome, with low rates of integration, and is lost with cellular replication. Gene editing technology exploiting the CRISPR/Cas9 system has the potential to overcome this limitation.

This thesis explored the possibility of using recombinant AAV (rAAV) technology to treat CAH. There were three distinct facets that were examined: rAAV-mediated delivery of adrenocortical enzymes to the liver for extra-adrenal expression, exploration of capsid tropism for direct targeting of specific populations of adrenocortical cells and specific editing of the Cyp21a1 locus in vivo.

This thesis sets the foundation for overcoming the biological properties of the adrenal cortex that renders standard rAAV gene therapy for CAH unsuitable, through delivering adrenocortical genes to a stable organ outside the adrenal, developing strategies to determine capsid tropism for the adrenocortical cells and successfully editing the Cyp21a1 locus with biological effect.