Background：Microscopic polyangiitis (MPA) is a necrotizing vasculitis which involves small- and medium-sized vessels. It is associated with the presence of anti-neutrophil cytoplasmic antibodies with a perinuclear staining pattern (p-ANCA). The kidney and lung are the organs primarily affected. MPA is rare in children, and easily misdiagnosed. In this work we describe a complete course of this disease. Case presentation: An 11-year-old girl with a one-month cough and hemoptysis, showed no improvement after imipenem-cilastatin treatment. P-ANCA, and microscopic haematuria and proteinuria, were positive, and a chest CT revealed an area of shadow in bilateral lower lobes of the lungs. Renal biopsies revealed crescentic glomerulonephritis. MPA was diagnosed based on these observations. The patient showed dramatic clinical and imaging improvement after immunosuppressive treatment. Conclusion: The organs and systems most affected by MPA in children, are the lungs (about 80%), kidneys (about 80%), cutaneous involvement (about 20%), nervous system involvement (about 16%), and gastrointestinal involvement (about 16%). Reasonable care should be taken in examining those patients, while biopsies of the kidney or any other of the organs remain the gold standard for diagnostic purposes. Pulmonary involvement may be the initial symptom of MPA, which is often misdiagnosed as pneumonia and antibiotics are used at the beginning of the disease. Patients with hemoptysis should undergo a comprehensive examination, including urine routine, to determine whether there is renal involvement, and an immunological index detection to determine whether it is an autoimmune disease.

Background: Lysinuric protein tolerance (LPI) is a rare autosomal, recessive, metabolic disease caused by mutations in the SLC7A7 gene. It was first reported in the Finnish population in 1965, and involved multiple organ systems like the digestive, blood, respiratory, nervous, urinary and other systems, due to a defect in the transport of the dialkylamino acid plasma membrane. Case presentation: A girl with severe malnutrition, underdevelopment and a long-term history of hepatosplenomegaly, presented with recurrent fever, cough and shortness of breath. Computer tomography (CT) revealed that she had a considerable lung infection, and the results of laboratory tests showed that she had moderate anemia. The maximum value of type B natriuretic peptide (BNP) was 6076 ng/L (0-300). In this course, the blood ammonia was 85.5 μmol/L (11-40), the serum ferritin was 3827 ng/mL (10-120), the complement 3 was 237 mg/L (790-1520), complement 4 was 53.1 mg/L (100-400), the titre of anti-nuclear antibody (ANA) was 1:320 and the anti-dsDNA antibody was positive. The patient died of severe pneumonia at 5 years old. A genetic test indicated that the patient’s SLC7A7 gene had a compound heterozygous mutation, including c.724T>C chr14-23248048 p.W242R and c.719C>T chr14-23248053 p.S240L, inherited from the patient’s father and mother, respectively. Conclusions: The patient was diagnosed with LPI with systemic lupus erythematosus (SLE), and severe pneumonia, and her SLC7A7 gene had a compound heterozygous mutation.