Supplementary Material for: Nephrolithiasis associated to Nephrocalcinosis is Primarily Composed of Carbonate Apatite

Introduction:
This study was designed to determine the mineral composition of calculi in nephrocalcinosis with nephrolithiasis, diagnose the underlying disease and monitor the course of renal function in patients with nephrocalcinosis-nephrolithiasis.
Methods:
Renal calculi extruded in a series of eight patients with nephrocalcinosis were analysed using Fourier transmission infrared spectrometry. In four patients, next generation sequencing (NGS) using a nephrocalcinosis-nephrolithiasis panel was performed to determine the nature of the underlying disease. In addition, longitudinal analysis of renal function was performed in all patients.
Results:
Seven patients revealed carbonate apatite as sole constituent of renal calculi. One patient showed a mixed composition of dicalcium phosphate dihydrate/carbonate apatite at first analysis, yet in subsequent episodes also had calculi composed of pure carbonate apatite. Further molecular analysis displayed distal renal tubular acidosis in two of four patients, that consented to sequencing. No known genetic defect could be found in the other two cases. In line with prior reports, decline of renal function was dependent on underlying disease. Distal renal tubular acidosis revealed a progressive course of renal failure, whereas other causes showed stable renal function in long term analysis.
Conclusion:
Nephrocalcinosis with nephrolithiasis is a rare condition with heterogenous etiology. Yet mineral composition of renal calculi predominantly consisted of pure carbonate apatite. This uniform finding is similar to subcutaneous calcifications of various origin and might propose a general principle of tissue calcification. Progressive decline of renal function was found in distal renal tubular acidosis, whereas other conditions remained stable over time.

引言：
本研究旨在明确伴肾结石病（nephrolithiasis）的肾钙质沉着症（nephrocalcinosis）患者结石的矿物组成，诊断其潜在病因，并监测这类患者的肾功能变化进程。

方法：
本研究采用傅里叶透射红外光谱法（Fourier transmission infrared spectrometry），对8例确诊肾钙质沉着症患者的排出肾结石进行分析；对其中4例患者，采用肾钙质沉着症-肾结石病相关测序面板开展下一代测序（next generation sequencing, NGS），以明确其潜在病因；此外，对所有患者均进行了肾功能纵向追踪分析。

结果：
7例患者的肾结石仅由碳酸磷灰石（carbonate apatite）构成。1例患者首次检测显示结石为二水合磷酸氢钙（dicalcium phosphate dihydrate）/碳酸磷灰石混合组成，但后续排出的结石均为纯碳酸磷灰石。进一步的分子检测显示，4例同意接受测序的患者中，2例存在远端肾小管酸中毒（distal renal tubular acidosis）；剩余2例患者未检出已知的遗传缺陷。与既往研究报道一致，肾功能减退情况与潜在病因密切相关：合并远端肾小管酸中毒的患者肾功能衰竭呈进行性进展，而其他病因患者的肾功能在长期追踪中保持稳定。

结论：
伴肾结石病的肾钙质沉着症是一类病因异质性较强的罕见疾病，但其肾结石的矿物组成多为纯碳酸磷灰石。这一统一的发现与多种病因所致的皮下钙化表现相似，或可揭示组织钙化的通用机制。合并远端肾小管酸中毒的患者肾功能呈进行性减退，而其他病因患者的肾功能则长期保持稳定。