Progressive myoclonic epilepsy as an adult-onset manifestation of Leigh syndrome due to m.14487T>C

BACKGROUND

m.14487T>C, a missense mutation (p.M63V) affecting the ND6 subunit of complex I of the mitochondrial respiratory chain, has been reported in isolated childhood cases with Leigh syndrome (LS) and progressive dystonia. Adult-onset phenotypes have not been reported.

OBJECTIVES

To determine the clinical-neurological spectrum and associated mutation loads in an extended m.14487T>C family.

METHODS

A genotype-phenotype correlation study of a Belgian five-generation family with 12 affected family members segregating m.14487T>C was carried out. Clinical and mutation load data were available for nine family members. Biochemical analysis of the respiratory chain was performed in three muscle biopsies.

RESULTS

Heteroplasmic m.14487T>C levels (36-52% in leucocytes, 97-99% in muscle) were found in patients with progressive myoclonic epilepsy (PME) and dystonia or progressive hypokinetic-rigid syndrome. Patients with infantile LS were homoplasmic (99-100% in leucocytes, 100% in muscle). We found lower mutation loads (between 8 and 35% in blood) in adult patients with clinical features including migraine with aura, Leber hereditary optic neuropathy, sensorineural hearing loss and diabetes mellitus type 2. Despite homoplasmic mutation loads, complex I catalytic activity was only moderately decreased in muscle tissue.

INTERPRETATION

m.14487T>C resulted in a broad spectrum of phenotypes in our family. Depending on the mutation load, it caused severe encephalopathies ranging from infantile LS to adult-onset PME with dystonia. This is the first report of PME as an important neurological manifestation of an isolated mitochondrial complex I defect.

Growth stimulatory angiotensin II type-1 receptor is upregulated in breast hyperplasia and in situ carcinoma but not in invasive carcinoma

Two different receptors which bind angiotensin II specifically have been identified in humans and were designated angiotensin II type-1 receptor (AT1) and angiotensin II type-2 receptor (AT2). They only have 34% sequence homology and act through different signalling pathways. AT1 stimulation has been implicated in hypertrophy and hyperplasia in various tissues. In order to study the involvement of AT1 in tissues from controls (n=10) and patients with hyperplasia (n=33), ductal carcinoma in situ (DCIS) (n=23) and invasive carcinoma of the breast (n=25), we tested biopsies and breast-derived cell lines using immunocytochemistry, in situ hybridisation and cell proliferation techniques. The results show specific overexpression of AT1 receptor on the cytoplasmic membrane of cells of hyperplastic lesions with and without atypia and on DCIS of the breast. Evidence for growth stimulation is provided by in vitro experiments showing growth induction by angiotensin II of T47D cells which express the AT1 but not the AT2 receptor. The expression of AT1 on the cell membrane disappears in invasive breast cancer cells suggesting a regulatory pathway which is no longer needed in invasive carcinoma. The specific AT1 expression upregulation might well be an important step in the pathogenesis of hyperplasia of the breast, which is regarded as a precursor lesion for breast cancer.

Distribution of type-1 and type-2 angiotensin receptors in the normal human lung and in lungs from patients with chronic obstructive pulmonary disease

This study was designed to examine the cellular distribution of the angiotensin II type-1 (AT1) and type-2 (AT2) receptors in the normal human and pathological human lung. Riboprobes were prepared against specific portions of each receptor DNA and labelled with FITC for detection using an anti-FITC antibody in combination with the alkaline phosphatase-anti-alkaline phosphatase technique and new Fuchsin. These were used to detect the presence of receptor mRNA in the lung. Specific antibodies were used to detect receptor protein in cells by immunocytochemistry. Image analysis was used in order to semi-quantify receptor density. AT1 receptor mRNA and protein were localised on vascular smooth muscle cells, macrophages and in the stroma underlying the airways epithelium probably relating to underlying fibroblasts. The AT1 receptor protein was not expressed in the epithelium although there was a low level of mRNA. In contrast, AT2 receptor RNA and protein was observed in the epithelium, with strong staining on the bronchial epithelial cell brush border and also on many of the underlying mucous glands. The AT2 receptor was also present on some endothelial cells. These findings were supported by the presence of mRNA in each case. In patients with chronic obstructive pulmonary disease, there was a five- to sixfold increase in the ratio of AT1 to AT2 receptors in the regions of marked fibrosis surrounding the bronchioles. This correlated well with the reduced lung function as expressed by the forced expiratory volume.

MHC class II molecules are required for initiation of positive selection but not during terminal differentiation of human CD4 single positive thymocytes

Positive selection of T cell precursors is an MHC dependent, multistep process by which functionally mature CD4+8- helper and CD4-8+ cytotoxic single positive (SP) T cells are generated from immature CD4+8+ double positive (DP) thymocytes. We investigated the requirement for TCR/MHC class II interactions during different stages of positive selection of human CD4 SP thymocytes. We show that sorted CD69- CD4+8+ DP preselection thymocytes cultured in fetal thymus lobes of normal mice were subject to positive selection and differentiated to CD3(high) CD69+, mature CD8 SP, and CD4 SP cells. When cultured in thymus lobes from MHC class II-deficient mice, these precursors failed to develop into mature CD4 SP T cells, indicating that in the hybrid cultures, murine MHC class II molecules are required for the development of mature human CD4 SP T cells. We have previously identified CD4 SP intermediate thymocytes that have received at least some of the signals involved in positive selection, since these cells are CD69+, CD3/TCR(high), and CD8beta- but that are still phenotypically and functionally immature. Here we demonstrate that in contrast to preselection thymocytes, these CD4 SP intermediate thymocytes can give rise to phenotypically mature and functionally CD4 SP progeny both in normal and in MHC class II-deficient thymus lobes. These results suggest that TCR/MHC interactions are required for the initial stages of positive selection, but are not essential during terminal differentiation to functionally mature CD4 SP T cells.

MHC class II molecules are required for initiation of positive selection but not during terminal differentiation of human CD4 single positive thymocytes

Positive selection of T cell precursors is an MHC dependent, multistep process by which functionally mature CD4+8- helper and CD4-8+ cytotoxic single positive (SP) T cells are generated from immature CD4+8+ double positive (DP) thymocytes. We investigated the requirement for TCR/MHC class II interactions during different stages of positive selection of human CD4 SP thymocytes. We show that sorted CD69- CD4+8+ DP preselection thymocytes cultured in fetal thymus lobes of normal mice were subject to positive selection and differentiated to CD3(high) CD69+, mature CD8 SP, and CD4 SP cells. When cultured in thymus lobes from MHC class II-deficient mice, these precursors failed to develop into mature CD4 SP T cells, indicating that in the hybrid cultures, murine MHC class II molecules are required for the development of mature human CD4 SP T cells. We have previously identified CD4 SP intermediate thymocytes that have received at least some of the signals involved in positive selection, since these cells are CD69+, CD3/TCR(high), and CD8beta- but that are still phenotypically and functionally immature. Here we demonstrate that in contrast to preselection thymocytes, these CD4 SP intermediate thymocytes can give rise to phenotypically mature and functionally CD4 SP progeny both in normal and in MHC class II-deficient thymus lobes. These results suggest that TCR/MHC interactions are required for the initial stages of positive selection, but are not essential during terminal differentiation to functionally mature CD4 SP T cells.