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L Fallon

Publications and source records attributed to L Fallon.

12 recordsLinked to original sources
PubMed2001

Photochemically removable silyl protecting groups.

Several o-phenol-containing alkoxyvinylsilanes were prepared and their photochemistry was investigated. These materials were prepared via hydrosilylation of the corresponding o-acetoxy arylacetylenes. Two major classes of photochemical processes were identified in these reactants: trans-->cis isomerization, leading to an intramolecular nucleophilic substitution process at silicon, and 1,5-silyl shift, leading to an unsymmetrical dialkoxysilane. The major outcome of this work is a novel class of photochemically removable protecting groups. Two alkyl substitutions on silicon, the dimethyl and diisopropyl, were examined. The latter is more stable and is preferred for protecting groups that must tolerate multiple steps or reagents. Protection of alcohols is generally performed starting with the arylethynyl acetate, which can be subjected to hydrosilylation, alcohol substitution, and acetate deprotection without isolation of intermediates. Two groups were studied in detail, the phenol and 2-naphthol vinyl silane derivatives. A variety of primary and secondary alcohols were protected with these reagents. These groups can be deprotected cleanly and in high yield by irradiation from 250 to 350 nm.

Acetylene↗
PubMed2000

Characterization and clinical implications of marker chromosomes identified at prenatal diagnosis.

Eighteen fetuses with marker chromosomes were detected at diagnostic amniocentesis in our laboratory among 15 781 amniocentesis samples. Using combined approaches, conventional cytogenetics including special stain techniques and fluorescence in situ hybridization (FISH), we successfully characterized 15 of them, which assisted subsequent genetic counselling. Six marker chromosomes were of sex chromosome origin, each of which substituted a missing sex chromosome, and 12 were supernumerary marker chromosomes (SMCs). Nine of the SMCs were proven to be of autosomal origin. Of those autosomal SMCs, five originated from chromosome 15, two from chromosome 18, one from chromosome 12 and one from chromosome 1. Among 16 marker chromosomes with adequate follow-up information, 50% were benign including four sex chromosome markers and four autosomal markers. Two thirds of de novo marker chromosomes were associated with abnormal outcomes, while all inherited ones were benign regardless of their parental origin. Our study demonstrated that molecular characterization of prenatal marker chromosomes is of great significance in facilitating phenotype-genotype correlation.

Amniocentesis↗
PubMed1999

Preimplantation genetic diagnosis for spinal muscular atrophy type I.

OBJECTIVE: Couples with children who have spinal muscular atrophy type I (SMA) face a 25% risk of having affected offspring with spontaneous conception. Preimplantation genetic testing (PGT) is possible for the deletions in the survival motor neuron (SMN) gene that have been identified in 98% of SMA type I cases. PGT would provide new reproductive options for families at risk for SMA. METHODS: Three couples with previously affected children confirmed by DNA testing each underwent in vitro fertilization (IVF) and PGT of the resulting embryos. One or two blastomeres were biopsied from each embryo and analyzed for deletions in exons 7 and 8 of the SMN gene. RESULTS: Nine embryos were predicted to be unaffected, three to be affected, and one embryo could not be interpreted. One of three patients receiving transfer of unaffected embryos became pregnant with twins. CONCLUSIONS: Preimplantation genetic testing provides a means for couples at risk for spinal muscular atrophy type I to reduce their chance of initiating an affected pregnancy.

Adult↗
PubMed1999

Fragile X premutation is a significant risk factor for premature ovarian failure: the International Collaborative POF in Fragile X study--preliminary data.

The preliminary results of an international collaborative study examining premature menopause in fragile X carriers are presented. A total of 760 women from fragile X families was surveyed about their fragile X carrier status and their menstrual and reproductive histories. Among the subjects, 395 carried a premutation, 128 carried a full mutation, and 237 were noncarriers. Sixty-three (16%) of the premutation carriers had experienced menopause prior to the age of 40 compared with none of the full mutation carriers and one (0.4%) of the controls. Based on these preliminary data, there is a significant association between fragile X premutation carrier status and premature menopause.

Adolescent↗
PubMed1996

Molecular fragile X screening in normal populations.

In December, 1993, we initiated a pilot project in which DNA fragile X (fraX) testing was offered during routine prenatal or genetic counseling to all pregnant women seen at the Genetics & IVF Institute, most of whom were referred for the indication of advanced maternal age. A brochure on fragile X syndrome was sent to each patient prior to her appointment and was reviewed by a counselor or physician during the counseling session. As of June 1995, 3,345 patients were offered testing; 474 women with no identified family history of mental retardation or learning disability and 214 women with a positive family history accepted the test on a self-pay basis. The second population screened was 271 potential donors in our anonymous egg donor program. DNA from blood was tested by Southern blot using EcoRI/EagI and StB12.3. If an expansion was detected, CGG repeat number was determined by PCR-based analysis. Among the 474 patients with unremarkable family histories, three fraX carriers were identified (repeat sizes = 60+), whereas none were found in the 214 patients with a positive family history. Among the potential egg donors, two high borderline patients were identified (repeat sizes = between 50 and 59). Our ongoing study indicates that screening of pregnant or preconceptual populations for fraX carrier status using DNA testing is accepted by many patients and is an important addition to current medical practice.

Chorionic Villi Sampling↗
PubMed1994

Management of ureteral stenosis after renal transplantation.

BACKGROUND: Ureteral stenosis is the most common urologic complication of renal transplantation. Preferred management options for this complication vary among centers. Ureteral stenosis occurred in 24 (3.4 percent) of 692 consecutive renal transplants. The diagnosis was confirmed by antegrade pyelography after ultrasonography in all instances. An attempt was made to treat all patients by percutaneous stenting, usually with dilatation of the ureter, which was possible in 21 patients. In three patients, a wire could not be passed across the stricture and these patients were treated surgically. STUDY DESIGN: The patients were divided into two groups. Patients in group 1 (14 patients) presented within three months from the date of transplantation and patients in group 2 (seven patients) presented after three months. RESULTS: The site of stenosis was the ureterovesical junction in 80 percent of the patients and the uretero-pelvic junction in 20 percent. Urinary tract infection occurred in 70 percent of the patients in group 1 and 100 percent of patients in group 2. The success rate of percutaneous stenting was 71 percent (ten of 14 patients) in group 1, but only 29 percent (two of seven patients) in group 2. The failures were treated by repeated stenting (one patient in each group) or by operation. One allograft (7 percent) was lost in group 1 and two (28 percent) were lost in group 2. The average follow-up period was 38 months in group 1 and 56 months in group 2. There was no mortality in this series. CONCLUSIONS: Ureteral stenosis in the early postrenal transplant period can be safely and effectively treated by percutaneous dilatation and stenting, with few side effects and long-term success. This method is specially efficacious in patients who present within three months from the time of their transplant. In patients who have ureteric strictures developing after three months from transplantation, percutaneous stenting is of limited value and most patients require surgical correction.

Adult↗
PubMed1967

An electromechanical analyzer using histogram techniques.

In behavioral studies it is often necessary to classify events and store the number of events occurring in each classification. The classification requirements may be either functions of amplitude (i.e., intensity, force, peaks, etc.) or time (i.e., duration, interval, etc.). The following describes an analyzer capable of classifying events according to their duration, interval, or time of occurrence, and storing and displaying the number of such events in each classification.

Behavior↗