tailieunhanh - Introduce of genetic counseling and chromosome abnormalities (Fifth edition): Part 2

(BQ) Continued part 1, part 2 of the document Introduce of genetic counseling and chromosome abnormalities (Fifth edition) has contents: Disorders associated with aberrant genomic imprinting, reproductive cytogenetics, disorders of sex development, noxious agents, and other contents. Invite you to refer. | Introduce of genetic counseling and chromosome abnormalities (Fifth edition): Part 2 PART FOUR DISORDERS ASSOCIATED WITH ABERRANT GENOMIC IMPRINTING 18 UNIPARENTAL DISOMY AND DISORDERS OF IMPRINTING UNIPARENTAL DISOMY IS A FASCINATING Maternal UPD 20 and important pathogenetic mechanism, albeit that Pseudohypoparathyroidism type 1B it is the basis of only a small number of well- defined clinical conditions. At the outset, we may list the Some of these can be due to genetic causes other following nine well- described uniparental disomy than uniparental disomy, and for convenience we (UPD)1 syndromes, representing chromosomes include a discussion of the other causes in this chap- 6, 7, 11, 14, 15, and 20, approximately in order of ter. In a category by itself, UPD can be the cause frequency: of homozygosity for an autosomal recessive gene. Nevertheless, the fact remains that most UPDs Beckwith- Wiedemann syndrome appear to be without any phenotypic consequence, Prader- Willi syndrome and a number of syndromes that had originally Angelman syndrome seemed fair candidates turned out not to be due to Silver- Russell syndrome UPD (Kotzot 2002). Kagami syndrome A distinction is to be made between UPD Temple syndrome where both chromosomes are identical (uni- Transient neonatal diabetes parental isodisomy, UPID) and where they are 1  As a general rule, abbreviations for “uniparental disomy” are in uppercase (UPD, UPHD, UPID) when making broad reference to the concept of uniparental disomy/ heterodisomy/ isodisomy, and in lowercase (upd, uphd, upid), according to the rules of cytogenetic nomenclature, when attention is more focused upon a specific case.   •  387 (a) different (uniparental heterodisomy, UPHD) (Fig. 18– 1a). UPD is normally demonstrable only at the molecular level: Typically, although not invariably, the UPD pair of chromosomes are cytogenetically normal, and the (classical) kary- otype .