Prenatal diagnosis of tetrasomy 18p using multiplex fluorescent PCR and comparison with a variety of techniques.

We report genetic characterization of isochromosome 18p using a combination of cytogenetic and molecular genetic methods, including multiplex fluorescent PCR. The patient was referred for chorionic villus sampling (CVS) due to advanced maternal age and maternal anxiety. The placental karyotype was 47,XX,+mar, with the marker having the appearance of a small supernumerary isochromosome. Because differentiating between isochromosomes and other structural rearrangements is normally very difficult, a variety of genetic tests including fluorescence in situ hybridization (FISH), PCR, and multiplex fluorescent PCR were undertaken to determine chromosomal origin and copy number and, thus, allow accurate diagnosis of the corresponding syndrome. FISH determined that the marker chromosome contained chromosome 18 material. PCR of a variety of short tandem repeats (STRs) confirmed that there was at least one extra copy of the maternal 18p material. However, neither FISH nor PCR could accurately determine copy number. Multiplex fluorescent PCR (MF-PCR) of STRs simultaneously determined that: (1) the marker included 18p material; (2) the marker was maternal in origin; (3) allele copy number indicated tetrasomy; and (4) contamination of the sample could be ruled out. Results were also rapid with accurate diagnosis of the syndrome tetrasomy 18p possible within 5 hours.

Using MF-PCR to diagnose multiple defects from single cells: implications for PGD.

Single cell genetic analysis is generally performed using PCR and FISH. Until recently, FISH has been the method of choice. FISH however is expensive, has significant misdiagnosis rates, can result in interpretation difficulties and is labour intensive making it unsuitable for high throughput processing. Recently fluorescent PCR reliability has increased to levels at or surpassing FISH whilst maintaining low cost. However, PCR accuracy has been a concern due to allelic dropout. Multiplex PCR can now increase accuracy by using multiple markers for each chromosome to firstly provide diagnosis if markers fail and/or secondly confirm diagnosis. We compare a variety of diagnostic methods and demonstrate for the first time a multiplex PCR system providing simultaneous diagnosis and confirmation of the major aneuploidy chromosomes (21,18,13) and sex as well as DNA fingerprint in single cells. We also discuss the implications of using PCR for aneuploidy screening in preimplantation genetic diagnosis.

Identifying the origin of single corneal cells by DNA fingerprinting: part I--implications for corneal limbal allografting.

PURPOSE: To demonstrate that the combination of impression cytology and single cell DNA fingerprinting represents a powerful tool that is suitable for detecting transplanted cells after corneal limbal allografting. METHODS: Fifty single cells were obtained by corneal impression cytology from 12 patients undergoing cataract surgery. Individual cells were isolated from samples by micromanipulation. Polymerase chain reaction and short tandem repeat profiling was used to obtain forensic standard "DNA fingerprints" from single cells. Blood samples taken at the time of impression cytology provided control "fingerprints." RESULTS: Informative DNA fingerprints were obtained from all corneal samples and 66% (33 of 50 cells) of isolated single cells. Of all fingerprints obtained, most (91%, 30 of 33 fingerprints) corneal fingerprints matched corresponding blood sample fingerprints. At least one corneal fingerprint matched the corresponding blood sample fingerprint in 83% (10 of 12 patients) of the patients in the study. CONCLUSIONS: This extremely specific single cell DNA fingerprinting system permits accurate identification of individual corneal epithelial cells, allowing very reliable determination of their origin, which will enable host and donor cells to be distinguished from each other after keratolimbal allografting procedures, even if the host and donor are the same sex or siblings. These DNA fingerprinting methods allow assessment of quality and quantity of donor cell survival, as well as survival time. The extreme sensitivity and accuracy of the technique means that should contamination occur, it would be identified, thus ensuring meaningful results.

Identifying the origin of single corneal cells by DNA fingerprinting: part II-- application to limbal allografting.

PURPOSE: Successful limbal allotransplantation allows regression of limbal stem cell deficiency features. Transplant survival is presumed if clinical improvement occurs. However, positive proof of surviving transplanted stem cells remains difficult. This follow-up study attempted to prove donor cell survival 5 years after limbal stem cell allograft in one woman with aniridia. METHODS: Impression cytology and single-cell DNA fingerprinting were used to investigate a previously studied patient. Corneal epithelial cells were harvested from five sites and isolated by micromanipulation. Polymerase chain reaction and short tandem repeat profiling were used to obtain forensic standard "DNA fingerprints" from single cells. (The technique is described in the preceding article, Part I.) Blood samples yielded host and donor DNA for comparison. Negative controls were performed for impression cytology and polymerase chain reaction. Simultaneous micro-scrape samples were also taken. RESULTS: Impression cytology samples permitted informative DNA fingerprints from all corneal sites and represented 76% (23/30) of tested cells. Fifty percent (15/30) of the fingerprints were "specific" but 83% (19/23) matched the host DNA fingerprint. The remaining 17% (4/23) represented contamination from various sources. Specific fingerprints were obtained in 55% (10/18) of the cells from micro-scrape samples. All samples giving sufficient information matched the host DNA fingerprint. All tested blood samples gave specific fingerprints. None of the sampled corneal cells gave a donor DNA fingerprint. CONCLUSIONS: In a single patient, no detectable long-term donor cell survival exists at 5 years. Positive identification would have provided unequivocal proof of donor cell survival. This technique gives useful information even if contamination occurs.

Reconstitution of rabbit sarcoplasmic reticulum calcium ATPase in a series of phosphatidylcholines containing a saturated and an unsaturated chain: suggestion of an optimal lipid environment.

The calcium-dependent ATPase from sarcoplasmic reticulum of rabbit has been purified and reconstituted in dispersions containing pure phosphatidylcholines. Each phosphatidylcholine (PC) had palmitate (16:0) at the sn-1 position of glycerol and stearate (18:0), oleate (18:1), linoleate (18:2), arachidonate (20:4), or docosahexaenoate (22:6) at the sn-2 position. The activities and activation energies of the enzyme indicated that the best enzyme function occurred when 16:0-18:1 PC or 16:0-18:2 PC was the lipid in which the ATPase was embedded. Circular dichroism measurements made as a function of temperature suggested that the protein in 16:0-18:0 and 16:0-18:1 PC behaved most like sarcoplasmic reticulum or purified ATPase. The results suggest that there may be an optimal lipid environment for the ATPase which is provided by 16:0-18:1 PC and 16:0-18:2 PC, the two most common lipids of the sarcoplasmic reticulum.

Phosphatidylcholine-cholesterol interactions: bilayers of heteroacid lipids containing linoleate lose calorimetric transitions at low cholesterol concentration.

Model membranes composed of cholesterol plus one of two phosphatidylcholines (PC), each containing a saturated and a dienoic acyl chain, have been studied by differential scanning calorimetry. The gel to liquid-crystalline phase transition temperature of 1-palmitoyl-2-linoleoyl PC was -19.5 degrees C and that of 1-stearoyl-2-linoleoyl PC was -13.7 degrees C. The addition of cholesterol to the phosphatidylcholines in aqueous dispersion resulted in the progressive removal of the phase transition as observed by differential scanning calorimetry. Per mole of sterol in the membrane, cholesterol was more effective at reducing the enthalpy change of the phase transitions of these bilayers containing dienoic phosphatidylcholines than it is in eliminating the transition of membranes made with other phospholipids that contain more saturated chains. No transitions in membranes made with palmitoyl-linoleoyl PC or stearoyl-linoleoyl PC could be detected calorimetrically when 17 mol% cholesterol was present.