Nail-patella syndrome (NPS) is an autosomal dominant disease caused mostly by mutations in the LMX1B gene and is characterized by hypoplastic nails, hypoplastic patella, elbow deformities, glaucoma, and nephropathy, sometimes leading to kidney failure. The combination and the severity of symptoms vary greatly from patient to patient. Because a kidney biopsy may show nonspecific findings, patients with nephropathy alone may not be diagnosed without undergoing genetic testing. We examined the case of a 6-year-old girl with persistent high proteinuria who was not diagnosed by kidney biopsy but had a diagnosis of a de novo mutation in the LMX1B gene following genetic testing. Retrospectively, only the thumbs showed triangular lunulae, while the third and fourth fingers lacked skin creases over the distal interphalangeal joints, which is subtle but characteristic of NPS. Notifying pediatric nephrologists of these findings can help avoid unnecessary kidney biopsies and lead to early detection of the disease.