CYP17A1 and hyperinsulinemic hypoglycemia, familial, 4: The karyotype of the patient was 46, XX, and the analysis of the <i>CYP17A1</i> gene by Sanger sequencing revealed a novel homozygous deletion c.1052-1054CCT which led to isolated 17,20-lyase deficiency.<h4>Conclusion</h4>In conclusion, this study report an in-frame deletion which results in isolated 17, 20-lyase deficiency, and the mutation might be used for diagnosis in other patients with distinctive clinical symptoms.