Abstract

P 098

Correlation of functional and structural changes in the mitochondria of levator and orbicularis muscles from patients with congenital and acquired ptosis

Lorenz B.¹, Renner K.², Schroeder J.^3
1Abteilung für Kinderophthalmologie, Strabismologie, Ophthalmogenetik, Klinikum der Universität Regensburg, ²Institut für Funktionelle Genomik, Universität Regensburg, ³Institut für Pathologie der Medizinischen Fakultät der Universität Regensburg

Objective: Analysis of functional consequences of ultrastructural mitochondrial alterations in levator and orbicularis muscles (MLP, MO) from patients with congenital or acquired ptosis.
Methods: Prospective study. Analysis of the respiratory chain in fresh biopsies from MLP and MO by high-resolution respirometry (Oroboros) from patients with congenital and acquired ptosis. Correlation with electron microscopy (EM) findings. Respiratory activity was normalized to the mitochondrial matrix marker enzyme citrate synthase.
Results: At present, 6 patients have been included in the ongoing study (age 3-70 y), 3 of them showed a “borderline-mitochondriopathy”, and 3 a full spectrum mitochondrial cytopathy. Mitochondrial lesions ranged from increase in mitochondria number to structural alterations including enlarged mitochondria, pleomorphy, matrix alterations and abnormal cristae observed in both, LMP and MO. Concerning functionality, the OMs were quite homogenous. In LMP, the degree of functional damage correlated better with the occurrence of abnormal cristae than with the level of structural changes. Overall respiratory capacity and activity of single enzymes, related to citrate synthase activity, were reduced in all LMPs normalised to one patient who had a mechanically acquired ptosis. In one patient complex I activity was reduced by 70 % and complex II by about 60%. One patient showed a strong reduction in the coupling of the respiratory chain to the ATP-synthase and therefore in ATP production.
Conclusions: The high percentage of structural mitochondrial alterations in patients with congenital and acquired ptosis¹ is confirmed by the present study. Respiratory capacity, related to citrate synthase activity, was reduced in MLPs. This counts for an altered surface to volume ratio, but could also be explained by the alterations of the cristae. The diagnostic relevance of the functional data has to be evaluated in further studies.
¹B. Wabbels, J. Schroeder, B.Voll, H. Siegmund, B. Lorenz, Graefe´s Arch Ophthal in press

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