Lysinuric protein intolerance (LPI) is an autosomal recessively inherited inborn error of metabolism (IEM) caused by the defect in the dibasic cationic amino acid transporter found on the basolateral membrane of the lung, small intestine, and kidney due to mutations in the SLC7A7 gene, which encodes the y+LAT1 protein. LPI may present as an acute hyperammonemic episode or as chronic symptoms. Major clinical symptoms are feeding problems, vomiting and diarrhea, failure to thrive, hepatosplenomegaly, and cytopenia. We present a delayed diagnosis of symptomatic LPI with a homozygous mutation in the SLC7A7 gene. A 15-year-old girl was referred to our clinic due to growth retardation and diarrhea. Physical examination showed short stature, retarded puberty, and hepatosplenomegaly. Laboratory tests showed normal complete blood count and biochemical analyses except elevated aspartate aminotransferase, triglyceride, total cholesterol, and ferritin. Peripheral blood smear and hemoglobin electrophoresis were within normal limits. Bone marrow analysis showed hemophagocytic cells. Postprandial ammonium level was found elevated. Low lysine, arginine, and ornithine and elevated glycine and alanine in plasma amino acid analysis and high amount of lysine and slightly elevated arginine and ornithine excretion in urine were detected. Molecular genetic analysis of the SLC7A7 gene showed a previously reported homozygous mutation. Low protein diet, sodium benzoate, l-carnitine, low-dose l-citrulline, and calcium replacement were initiated. The patient is now in good condition still being followed up in our department. LPI is a metabolic disorder with multi-systemic involvement that may have severe consequences if left untreated. Initiation of early treatment is essential for the prevention of severe chronic complications. Also, confirmation of the genetic defect may provide the parents to have healthy offsprings in the future with the help of genetic counselling and preimplantation genetics.

中文翻译：

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赖氨酸尿蛋白不耐受：一个被忽视的诊断

赖氨酸尿蛋白不耐受 (LPI) 是一种常染色体隐性遗传的先天性代谢缺陷 (IEM)，由 SLC7A7 基因突变导致肺、小肠和肾脏基底外侧膜上发现的二价阳离子氨基酸转运蛋白缺陷引起, 编码 y+LAT1 蛋白。LPI 可能表现为急性高氨血症发作或慢性症状。主要的临床症状是喂养问题、呕吐和腹泻、发育迟缓、肝脾肿大和血细胞减少。我们提出了 SLC7A7 基因纯合突变的症状性 LPI 的延迟诊断。一名 15 岁女孩因生长迟缓和腹泻被转诊至我们诊所。体格检查显示身材矮小、青春期发育迟缓和肝脾肿大。实验室检查显示全血细胞计数和生化分析正常，但天冬氨酸转氨酶、甘油三酯、总胆固醇和铁蛋白升高。外周血涂片和血红蛋白电泳均在正常范围内。骨髓分析显示噬血细胞。发现餐后铵水平升高。在血浆氨基酸分析中检测到低赖氨酸、精氨酸和鸟氨酸以及升高的甘氨酸和丙氨酸，检测到尿液中大量赖氨酸和略微升高的精氨酸和鸟氨酸排泄。SLC7A7 基因的分子遗传分析显示先前报道的纯合突变。开始低蛋白饮食、苯甲酸钠、左旋肉碱、低剂量左旋瓜氨酸和钙替代。患者目前情况良好，仍在我科接受随访。LPI 是一种多系统受累的代谢紊乱，如果不及时治疗可能会产生严重后果。早期治疗对于预防严重的慢性并发症至关重要。此外，在遗传咨询和植入前遗传学的帮助下，基因缺陷的确认可以为父母提供未来健康的后代。