BACKGROUND Karyomegalic interstitial nephritis (KIN) is a rare hereditary cause of chronic kidney disease. It typically causes progressive renal impairment with haemoproteinuria requiring renal replacement therapy before 50 years of age. It has been associated with mutations in the Fanconi anaemia-associated nuclease 1 (FAN1) gene and has an autosomal recessive pattern of inheritance. Leukocyte chemotactic factor 2 amyloidosis (ALECT2) is the third most common cause of amyloid nephropathy presenting with chronic kidney disease and variable proteinuria. We report a novel mutation in the FAN1 gene causing KIN and to our knowledge, the first case of concurrent KIN and ALECT. CASE PRESENTATION We describe the case of 44 year old Pakistani woman, presenting with stage four non-proteinuric chronic kidney disease, and a brother on dialysis. Renal biopsy demonstrated KIN and concurrent ALECT2. Genetic sequencing identified a novel FAN1 mutation as the cause of her KIN and she is being managed conservatively for chronic kidney disease. Her brother also had KIN with no evidence of amyloidosis and is being worked up for kidney transplantation. CONCLUSION This case highlights two rare causes of chronic kidney disease considered underdiagnosed in the wider population due to their lack of proteinuria, and may contribute to the cohort of patients reaching end stage renal disease without a renal biopsy. We report a novel mutation of the FAN1 gene causing KIN, and report the first case of concurrent KIN and ALECT2. This case highlights the importance of renal biopsy in chronic kidney disease of unclear aetiology which has resulted in a diagnosis with implications for kidney transplantation and family planning.

中文翻译：

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具有新的FAN1基因突变和并发ALECT2淀粉样变性的核仁型间质性肾炎。

背景技术核巨细胞性间质性肾炎（KIN）是慢性肾脏疾病的罕见遗传原因。它通常会导致进行性肾损害，伴有血蛋白尿，需要在50岁之前进行肾脏替代治疗。它已与Fanconi贫血相关的核酸酶1（FAN1）基因中的突变相关联，并具有遗传的常染色体隐性模式。白细胞趋化因子2淀粉样变性（ALECT2）是淀粉样肾病的第三大最常见病因，伴有慢性肾脏疾病和可变蛋白尿。我们报告FA​​N1基因中的一个新突变引起KIN，据我们所知，这是同时发生KIN和ALECT的第一例。病例介绍我们描述了一个44岁的巴基斯坦妇女的病例，该病人患有四期非蛋白尿性慢性肾脏疾病，并有一个正在透析的兄弟。肾活检显示KIN和并发ALECT2。基因测序鉴定出一个新的FAN1突变是其KIN的病因，并且她正在接受慢性肾脏疾病的保守治疗。她的兄弟也患有KIN，没有淀粉样变性病的证据，正在接受肾脏移植的检查。结论该病例突出了由于缺乏蛋白尿而在广泛人群中被诊断不足的两种慢性肾脏病的罕见原因，并且可能导致未进行肾脏活检的晚期肾脏疾病患者的队列研究。我们报告FA​​N1基因引起KIN的新型突变，并报告并发KIN和ALECT2的第一例。