Biomedical subjects
Publications and source records attributed to M Donlan.
Familial transmission of cytogenetically visible autosome deletions is rare in humans. We describe here a case of mother to son transmission of an interstitial deletion of the distal long arm of chromosome one, breakpoints q42.1q42.3. This is the smallest described deletion of this region to date.
Thirteen patients with hypopigmentation of the skin characteristic of hypomelanosis of Ito, and with developmental disabilities or structural malformations, or both, were examined at our center. Eight were found to have abnormal karyotypes in lymphocytes, fibroblasts, or both. No single clinical feature was predictive of chromosome imbalance in this group of patients. Cytogenetic findings included a balanced de novo X-autosome translocation; ring 10; 45,X/46,X,+ring; mosaic del 13q11 (fibroblasts); mosaic triploidy (fibroblasts); mosaic tetrasomy 12p (fibroblasts); mosaic apparently balanced 15;22 translocation (peripheral blood); and mosaic trisomy 18 (peripheral blood). Hypomelanosis of Ito is characterized by swirly hypopigmentation or depigmentation of the skin with or without other malformations. Autosomal dominant, autosomal recessive, and X-linked dominant inheritance have been suggested but not confirmed. Chromosomal aneuploidy has also been reported. We believe that hypomelanosis of Ito is an etiologically heterogeneous physical finding, and recommend karyotyping of multiple tissues of all patients with abnormal cutaneous pigmentation associated with developmental delay or structural malformations.
Variation in the observed spin lattice relaxation rate (Robs) interpreted as proton exchange dominated in sequences corresponding to part of promoters where RNA polymerase initiates mRNA synthesis has been observed by both Patel et al. and Reid and co-workers. A higher Robs was also seen in the TA pair of the GTG/CAC in the sequence corresponding to the lambda phage cro repressor binding site by Kyogoku et al. As we pointed out in the introduction, the one case where a three-dimensional structure for a turn of a helix is known shows clear structural heterogeneity which has led to detailed consideration of geometry of regulatory regions. Nussinov and collaborators have generalized the details of the Dickerson dodecomer to note potential similarities in operators including the lac system and the enhancer sequences described above. Like the steric considerations of Calladine and Dickerson and nearest neighbor structure analysis of Bubienko et al., the focus is on the geometry of a sequence leading to base tilt angles and potential overlap since they are measurable parameters. With the observation that the DNA molecule is both structurally and dynamically flexible, there will no doubt be many new variables that can be made as a function of DNA sequence. Biophysical chemists in some ways are like the intoxicated person searching for a lost key at a site different from where it was lost because that is where the light is best. Thus, each physical method has its most convenient observable. It is hoped that the above discussion illustrates that a very large and diverse set of biochemical results are awaiting detailed explanation in molecular terms using the illumination of high resolution physical techniques.
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