Therefore, a mutation in a single β-hemoglobin allele is sufficient to cause HS, while both α-hemoglobin alleles must be mutated to cause the disease (25, 26), Therefore, HS caused by SPTA1 gene mutations accounts for a smaller proportion (5%), and most SPTA1-HS cases only exhibit typical HS-related clinical manifestations when α-hemoglobin expression is reduced to less than 25% of normal levels (27, 28). This evidence concerns the gene SPTA1 and histiocytic sarcoma.