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Early development of the renal lesions in infantile cystinosis
1Division of Pediatric Endocrinology, University of Washington Medical School, Children's Hospital & Regional Medical Center, Seattle 98105, USA. pmahon@chmc.org
Insights
The "swan neck" deformity in cystinosis is acquired, developing after six months of age. This renal lesion correlates with Fanconi syndrome and cystine crystal accumulation in proximal tubules.
Area of Science:
- Nephrology
- Pediatric Pathology
- Medical Genetics
Background:
- Cystinosis is a rare genetic disorder characterized by lysosomal accumulation of cystine.
- Early identification of renal lesions is crucial for managing cystinosis and associated complications.
- The "swan neck" deformity of the proximal tubule is a recognized feature, but its origin (congenital vs. acquired) remains debated.
Observation:
- Renal function tests and kidney biopsies were performed on two infants with cystinosis at multiple time points from 5 to 14 months of age.
- Nephron microdissection and light microscopy did not reveal the "swan neck" deformity until after six months of life.
- Electron microscopy showed degenerative changes in proximal tubule cells preceding the development of the "swan neck" lesion.
Findings:
- The "swan neck" deformity appears to be an acquired lesion, developing postnatally.
- Fanconi syndrome manifestations correlated with the progression of the "swan neck" lesion.
- Cystine crystal-like spaces were observed in atrophic proximal tubule segments, temporally linked to lesion development.
Implications:
- These findings suggest that the "swan neck" deformity is a consequence of cystine accumulation and cellular damage.
- Understanding the acquired nature of this lesion can inform earlier diagnostic and therapeutic strategies for cystinosis.
- This study provides critical insights into the pathogenesis of renal dysfunction in infantile cystinosis.
Abstract:
To identify the early renal lesions in cystinosis, including whether the "swan neck" deformity of the proximal tubule is a congenital or an acquired lesion, we performed renal function tests and kidney biopsies on two cystinotic infants, on one at 5 and 14 months and on the other at 6 and 12 months of age. The "swan neck" deformity appears to be an acquired lesion for two reasons. First, the characteristic thin neck of the proximal tubule was not demonstrated by nephron microdissection or light microscopy until after 6 months of life. Second, electron microscopy revealed that prior to the development of the lesion, the tubular cells in the neck region of the proximal tubule were undergoing degenerative changes. Renal function tests indicated that the manifestations of the Fanconi syndrome correlated with the stages of development of the "swan neck" lesion. Minute crystalline spaces having some of the characteristics of lysosomal cystine crystals appeared in the early biopsies only in that portion of the proximal tubule which was undergoing atrophy to form the "swan neck" lesion observed in the later biopsies. These findings provide evidence of at least a temporal relationship between apparent cellular cystine accumulation and the development of the "swan neck" lesion and the Fanconi syndrome.
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