HBB and Schnyder corneal dystrophy: CRISPR–Cas9 and recombinant adeno‐associated virus serotype 6 (rAAV6) targeted editing of HSCs achieved homologous recombination of the HBB gene, effectively correcting SCD‐associated amino acid mutations at the HBB gene codon 6 (E6V) in HSPCs from multiple patients with SCD, realizing the treatment of patients with SCD.142