We show that PC-1 interacts with the SH3 domain of Nephrocystin-1 (NPHP1), the product of the NPHP1 gene mutated in nephronophthisis, an autosomal recessive disease characterized by a small cyst formation at the corticomedullary junction of the kidney [8], [9], [10]. The gene discussed is NPHP1; the disease is nephronophthisis.