Diagnosing sphingolipidoses in murine and human embryos

Preimplantation diagnosis of a lysosomal storage disorder by in situ enzymatic activity: 'proof of principle' in acid sphingomyelinase-deficient mice

Genetic diagnosis of preimplantation embryos (PGD) can substantially reduce the chance that at-risk couples have children afflicted with inherited diseases. However, PGD requires DNA,which is usually obtained from single cells following embryo biopsy. In addition, PGD requires that the genetic defect(s) causing the disorder be known. We have therefore developed an alternative to PGD, which we term preimplantation enzymatic diagnosis (PED). PED has several advantages over PGD, including the facts that it does not require embryo biopsy and that the gene defect(s) causing the disorder need not be known. We have demonstrated 'proof of principle' for this approach using embryos obtained from a mouse model (ASMKO mice) of acid sphingomyelinase (ASM)-deficient Niemann-Pick disease, an inherited lysosomal storage disorder. For this technique, fluorescently (BODIPY)-conjugated sphingomyelin was used to detect ASM activity in situ. Wild-type, preimplantation embryos degraded the substrate following a short 'pulse-chase' period, resulting in markedly reduced fluorescence compared to ASMKO embryos, which retained the fluorescent substrate. Thus, the two embryo types could be easily distinguished by fluorescent microscopy. The fluorescent sphingomyelin was not toxic to the embryos, and the entire procedure could be accomplished within 48 h without embryo biopsy. We suggest that PED may be useful for the preimplantation diagnosis of lysosomal storage disorders, and perhaps other enzymatic defects where similar in situ assay methods are available.

Pyrene-labeled lipids as tools in membrane biophysics and cell biology

Pyrene is one of the most frequently used lipid-linked fluorophores. Its most characteristic features are a long excited state lifetime and (local) concentration-dependent formation of excimers. Pyrene is also hydrophobic and thus does not significantly distort the conformation of the labeled lipid molecule. These characteristics make pyrene lipids well-suited for studies on a variety of biophysical phenomena like lateral diffusion, inter- or transbilayer movement of lipids and lateral organization of membranes. Pyrene lipids have also been widely employed to determine protein binding to membranes, lipid conformation and the activity of lipolytic enzymes. In cell biology, pyrene lipids are promising tools for studies on lipid trafficking and metabolism, as well as for microscopic mapping of membrane properties. The main disadvantage of pyrene lipids is the relatively large size of the fluorophore. Another disadvantage is that they require UV-excitation, which is not feasible with all microscopes.

Gaucher's disease in pregnancy

Gaucher's disease is an autosomal recessive lysosomal storage disease, resulting from a deficiency of the enzyme glucocerebrosidase, important for the physiologic recycling of cell membrane lipids. The clinical symptoms and disease presentations of Gaucher's disease are heterogeneous, including hepatosplenomegaly, bone "crisis" and fracture, anemia, thrombocytopenia and in some forms, rapid neurological decompensation. Similarly, the genetic variability of Gaucher's disease is diverse, and in some aspects affects phenotypic expression. Type 1 Gaucher's disease, however, usually present with less severe symptoms, at more advanced age, and is particularly amenable to enzyme replacement therapy with alglucerase. In type 1 patients with Gaucher's disease reproductive age is commonly reached and childbearing frequently desired with need for appropriate prenatal diagnosis, counseling and careful obstetrical surveillance. Although pregnancy concurrent with Gaucher's disease has been reported in the medical literature, only one small series of alglucerase treated Gaucher's disease during pregnancy exists. Without treatment, pregnancy concurrent with Gaucher's disease has several risks including an increased severity of anemia and thrombocytopenia that can potentiate postpartum bleeding, significant increases in organomegaly and possibly an increased spontaneous abortion rate. It is yet to be shown whether alglucerase reduces the risk of these complications during pregnancy and whether its use has any adverse effect on fetal development.