Genetics of Nail-Patella Syndrome Workup

Updated: Mar 24, 2016
  • Author: Julie Hoover-Fong, MD, PhD, FACMG; Chief Editor: Maria Descartes, MD  more...
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Workup

Laboratory Studies

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  • Annual screening urinalysis with microscopy is indicated in patients with nail-patella syndrome (NPS) to evaluate for proteinuria and hematuria. A urine protein-to-creatinine ratio or albumin-to-creatinine ratio is also indicated.
  • Annual blood pressure measurements and annual BUN and creatinine level assessments are indicated.
  • Consider 24-hour urine collection to quantitate protein and creatinine excretion if above screening results are abnormal.
  • LMX1B sequencing is diagnostic in the majority of patients. [8, 9, 10] LMX1B mutations in exons 2-6 can be found via DNA sequencing in 80-85% of patients with nail-patella syndrome and an additional 5% can be picked up with deletion and duplication analysis. Once a mutation is found, other family members can have targeted testing.
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Imaging Studies

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  • Radiography may reveal iliac horns, hypoplastic patellae or abnormal radial heads.
  • If joint surgery planned, conduct MRI of that joint to identify abnormal tendon, ligament, and/or muscle insertions and vessel distribution prior to surgery. Anatomy of joints in patients with nail-patella syndrome is typically abnormal.
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Other Tests

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  • Perform annual dilated ophthalmologic examination including slit-lamp quantification of intraocular pressure and visual fields.
  • Consider dual energy x-ray absorptiometry (DEXA) scanning to evaluate bone mineral content and density as surrogate indicator of bone strength. Bone mineral density is decreased by 8-20% in the hips of patients with nail-patella syndrome, and increased fractures have been reported.
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Procedures

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  • Renal biopsy may be indicated after referral to nephrologist for evaluation of progressive renal insufficiency, proteinuria, and hypertension in nail-patella syndrome.
  • Light microscopy reveals glomerulonephritis and basement membrane thickening; however, negative results do not rule out pathological processes in the kidney.
  • Electron microscopy can reveal ultrastructural changes, such as irregularities and thickening of the basement membrane and the presence of collagen-like fibrils within the basement membrane, which cannot be seen with light microscopy. These appearances are pathognomonic.
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Histologic Findings

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  • Increased lucency of the glomerular basement membrane resembles a moth-eaten appearance. A typical lesion consists of irregular basement membrane thickening, epithelial foot process fusion, and the presence of fibrillar collagenlike material within the basement.
  • Histological features are present even in patients without clinically evident renal involvement.
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