Thrombospondin type 1 domain-containing 7A (THSD7A) is a recently identified target
antigen of
idiopathic membranous nephropathy (iMN). The clinicopathological characteristics of THSD7A-associated MN are poorly characterised due to low prevalence among MN patients. Among 469 consecutive cases of pathologically confirmed MN diagnosed at four centres in Japan, 14 cases were confirmed positive for THSD7A by immunohistochemistry (3.0%). The prevalence of THSD7A-associated MN tended to be higher in northern Japan. Most cases demonstrated nephrotic-range
proteinuria (12/14 cases, 86%). In two patients,
cancer was detected at the time of renal biopsy (
small-cell carcinoma of the lung and prostatic
adenocarcinoma with neuroendocrine differentiation). Both tumours were negative for THSD7A. Four patients had concurrent or previous incidence of allergic diseases, including one patient with
Kimura's disease. Pathological analysis of kidney biopsy tissue revealed slight mesangial cell proliferation in three cases and spike formation in one case. Immunofluorescence studies demonstrated that
IgG subclass was mainly
IgG4-dominant/codominant (12/13, 92% cases), while the case with
prostatic cancer had an IgG2-dominant distribution. The immunostaining profile for components of the lectin complement pathways was not significant in three cases including two patients with
malignancy. One case was dual positive for THSD7A and PLA2R. Of 10 cases with known clinical follow-up data, 6 demonstrated reduced serum
creatinine and 8 presented reduced
proteinuria. In summary, although the major
IgG phenotype was usually
IgG4-dominant/codominant, clinical background was otherwise heterogeneous. Further investigation of regional differences in THSD7A-associated MN prevalence may reveal genetic and environmental risk factor and associated pathogenic mechanisms.