Calcified crystalline material in peripheral lymphocytes in choroideremia- a novel discovery

Abstract

Purpose : Although many retinal degeneration are restricted to the retina, we recently discovered that choroideremia (CHM) is a systemic disease (Zhang et al, 2015, in press, IOVS). Choroideremia was found to be associated with plasma and red blood cell membrane fatty acid abnormalities and peripheral lymphocyte crystals on electron microscopy. The purpose of the current prospective observational study is to assess the nature and extent of these peripheral blood cell nanocrystals and to compare them to those found in patients with Bietti’s Crystalline Dystrophy (BCD), an autosomal recessive retinal degeneration characterized by the presence of crystalline deposits in the retina.

Methods : We recruited three patients with BCD (CYP4V2 mutations), three patients with choroideremia (REP1 mutations) for this study, and three normal controls. Characterization of the phenotypes was done through medical history and physical exam. Fundus photography and spectral domain optical coherence tomography were performed for documentation. Genotyping was completed by whole exome sequencing and analyzed in silico by ENSEMBL, BLOSUM, SIFT and Polyphen. Peripheral blood samples were collected from patients and characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and proteinomics.

Results : Energy dispersive spectroscopy shows the chemical composition of the crystalline material in the blood of choroideremia patients to be calcium phosphate. This composition is identical to hydroxyapatite, a naturally occurring mineral found in bone, as well as in calcified tissue. This pathological form of calcification of blood cells, specifically lymphocytes, has not been described previously and was not found in normal controls. TEM and EDS analyses of the crystals in patients with BCS are currently underway.

Conclusions : Pathological calcification in peripheral lymphocytes in patients with choroideremia is a novel discovery. We are investigating whether similar calcium phosphate is found in our cohort of Bietti’s patients. Although the causes and implications of these calcifications are unknown, these findings are crucial to further elucidate the pathologic mechanisms in retinal degeneration, which may lead to photoreceptor loss and vision loss.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.