Perifoveal müller cell depletion in a case of macular telangiectasia type 2.

PURPOSE: To assess the histopathologic changes in a postmortem sample derived from an eye donor with macular telangiectasia (MacTel) type 2 to gain further insight into the cause of the disease. DESIGN: Clinicopathological case report. PARTICIPANTS: Postmortem tissue was collected from 5 different donors: 1 MacTel type 2 patient; 1 healthy control; 2 type 2 diabetic patients, 1 with retinopathy and 1 without retinopathy; and 1 patient with unilateral Coat's disease. METHODS: Macular pigment distribution in the posterior part of freshly dissected eyes was documented by macrophotography. Paraffin sections from both the macular and peripheral regions were assessed using antigen retrieval and immunohistochemistry to study the distribution of cell-specific markers. Blood vessels were visualized with antibodies directed against collagen IV and claudin 5; glial cells with antibodies against glial fibrillary acidic protein (GFAP), vimentin, glutamine synthetase (GS), and retinaldehyde binding protein (RLBP1, also known as CRALBP); microglia with an antibody against allograft inflammatory factor 1 (also known as Iba1); and photoreceptors with antibodies against rhodopsin and opsin. Using anatomic landmarks, the sections then were matched with the macular pigment distribution and a fluorescein angiogram of the patient that was obtained before the patient's death. MAIN OUTCOME MEASURES: Presence and distribution of macular pigment and cell-specific markers. RESULTS: Macular pigment was absent in the macula. Furthermore, abnormally dilated capillaries were identified in a macular region that correlated spatially with regions of fluorescein leakage in an angiogram that was obtained 12 years before death. These telangiectatic vessels displayed a marked reduction of the basement membrane component collagen IV, indicating vascular pathologic features. The presence of GFAP was limited to retinal astrocytes, and no reactive Müller cells were identified. Importantly, reduced immunoreactivity with Müller cell markers (vimentin, GS, and RLBP1) in the macula was observed. The area that lacked Müller cells corresponded with the region of depleted macular pigment. CONCLUSIONS: These findings suggest that macular Müller cell loss or dysfunction is a critical component of MacTel type 2, which may have implications for future treatment strategies.