Barraquer–Simons syndrome (BSS), a form of acquired partial lipodystrophy, is a rare condition characterized by
gradual loss of adipose tissue from the upper body, keeping intact the white adipose tissue of the lower extremities.
The etiology of BSS is not well understood, and clinical follow-up studies have not been assessed in these
patients. Moreover, no histological studies have been conducted during the active phase of the disease, and complement
system activation products have not been sought in the affected areas. The objective of this work was to
analyze the clinical, immunological and histological events in an 11-year-old girl with BSS over a 5-year follow-up
period. Clinical data were collected during six regular visits for a time period of 5 years. The circulating levels of
C3, C3adesArg (a product released upon C3 activation), C4 and immunoglobulins (Ig) were quantiﬁed in serum
while fat tissue from lipoatrophic areas was examined by immunohistochemical and immunoﬂuorescence
approaches. In her regular visits, no clinical or laboratory abnormalities had been observed in the patient, except
for the progression of lipoatrophy linked to the C3 hypocomplementemia and the occurrence of C3 nephritic factor.
Adipose tissue from the patient showed atrophied and dead adipocytes, an abnormal production of extracellular
matrix, and a remarkable accumulation of inﬁltrating CD68 macrophages and adipocyte precursors (marked
by c-Kit positiveness). Simultaneous detection of IgG, C3, C5a and C5b-9 proved the ongoing complement activity
and complement-directed injury within the adipose tissue. Our results showed the ﬁrst evidence that the complement
system hyperactivation occurs within the adipose tissue and is linked with fat loss in patients with BSS.