Mulibrey nanism (MUL) is a monogenic disorder with prenatal-onset growth 
failure, typical clinical characteristics, cardiopathy and tendency for a 
metabolic syndrome. It is caused by recessive mutations in the TRIM37 gene 
encoding for the peroxisomal TRIM37 protein with ubiquitin-ligase activity. In 
this work, the frequency and pathology of malignant and benign tumours were 
analysed in a national cohort of 89 Finnish MUL patients aged 0.7-76 years. The 
subjects had a clinical and radiological evaluation, and histological and 
immunohistocemical analyses on specimens obtained from biopsy, surgery or 
autopsy, were performed. The results show that the MUL patients have disturbed 
architecture with ectopic tissues and a high frequency of both benign and 
malignant tumours detectable in several internal organs. A total of 210 tumorous 
lesions were detected in 66/89 patients (74%). Fifteen malignancies occurred in 
13 patients (15%), seven of them in the kidney (five Wilms' tumours), three in 
the thyroid gland, two gynaecological cancers, one gastrointestinal carcinoid 
tumour, one neuropituitary Langerhans cell histiocytosis and one case of acute 
lymphoblastic leukaemia (ALL). Tumours detected by radiology in the liver and 
other organs mainly comprised strongly dilated blood vessels (peliosis), 
vascularized cysts and nodular lesions. The lesions showed strong expression of 
the endothelial cell markers CD34 and CD31 as well as the myocyte marker 
alpha-smooth muscle actin (alpha-SMA). Our findings show that MUL is associated 
with frequent malignant tumours and benign adenomatous and vascular lesions, as 
well as disturbed organ development.