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Other Constitutional Chromosome Diseases

GENERAL COMMENTS

  • Imbalances concerning gonosomes are less deleterious than those affecting autosomes; Imbalances leading to an excess of gene dosage (i.e. duplications, trisomies) are less deleterious than those resulting in a deficit (i.e. deletions, monosomies).

  • Bias of sampling: the most deleterious chromosome imbalances are not seen but result in early miscarriages; miscarriages and stillbirths occur in other syndromes, and only the less deleterious are compatible with life.

  • Some signs are characteristic of the disease. They are due to a gene effect or to the combination of genes effects. their association can be called a contiguous gene syndrome (see below).
    Other signs are aspecific of the region involved; they are the result of general gene imbalance and/or cell division disturbances, and may be found in many chromosome syndromes: growth retardation, microcephaly, mental retardation, low set ears ... can be found in various disease with no gene similarity.

  • Type/contertype: trisomy 4p syndrome (not herein described) exhibit some signs which are the opposite of del(4p) syndrome (e.g. flat/high forehead, aplasic/large glabella, prognatism/microretrognatism). In trisomy 4p, genes located in 4p are in 3 sets, while in del(4p) these genes are in only 1 set. This is an example of probable gene dosage specific effects.

  • Haploinsufficiency: is a term used in case of a deleted segment with deleterious effects; it means that the remaining haploid set of gene(s) is insufficient to allow a normal function.

  • Critical region: it was previously thought that a trisomy phenotype was due to the global excess of the extra chromosome (e.g. trisomy 21), and a deletion syndrome to the haploinsufficiency of the whole deleted segment. With the description of cases with overlapping imbalances, it became clear that some regions of imbalance had more deleterious effects, while others induced only mild disturbances. The critical segment is, in some instances, very narrow: band q22.3 is responsible of most of the trisomy 21 phenotype; it may even be smaller: the 200 kb critical segment in del(4p) syndrome. In the latter case, one has even evoked the notion of "contiguous gene syndrome".

  • Continuous genes syndrome: some Mendelian inherited diseases have been known for long, and their deleterious effect well described. It has happen that a given patient had presented with the addition of phenotypes from different inherited diseases. A well known example is that of a patient with the addition of Duchenne muscular dystrophy, chronic granulomatous disease, retinitis pigmentosa, and Mc Leod syndrome. This patient had a deletion in Xp21, where all these genes map.

  • Cryptic rearrangements/imbalances: it is likely that a percentage of chromosome imbalances remain undetected and/or undetectable: some of these imbalances are probably cause of major anomalies; the location of the chromosome imbalance may not be suspected if the phenotype is not reminiscent of a well known syndrome; others cryptic imbalances may have no, or slight effects, and will never be uncovered (another bias of sampling!).

     

    OTHER AUTOSOMES DISEASES

     

    A - DELETION 4p (Wolf-Hirschhorn syndrome / Pitt-Rogers-Dank syndrome)

     

    B - DELETION 5p (cri-du-chat syndrome)

     

    C - TRISOMY 8 MOSAICISM

     

    D - TRISOMY 9p

     

    E - TRISOMY 13 (Patau syndrome)

     

    F - DELETION 18p (Edwards syndrome)

  • IQ = 50; may have psychiatric behaviour.

     

    G - DELETION 18q

     

    H - TRISOMY 18

     

    DYSGONOSOMIES AND RELATED SYNDROMES

     

    A - TURNER SYNDROME

    In a few words, Turner syndrome (or Ullrich-Turner syndrome) is a syndrome of growth retardation and impuberism with frequent cardiovascular or renal malformation, normal intelligence, due to a chromosome imbalance: 45, X and variants.

     

    B - KLINEFELTER SYNDROME

    In a few words, Klinefelter syndrome is a syndrome of a normal or gynecoid male with normal intelligence or mild retardation, infertility, and possible behaviour or psychiatric problems, due to a chromosome imbalance: 47, XXY and variants.

     

    C - FRAXA and FRAXE SYNDROMES (Fragile Xq or fra(X)(q28))

    FRAXA

    FRAXE

     

    D - 47, XXX

     

    E - 48, XXXX and 49, XXXXX

     

    F - 47, XYY

     

    G - XX MALE SYNDROME

     

    H - XY FEMALE SYNDROME

     

    I - NOONAN SYNDROME

     

    OTHER CHROMOSOME IMBALANCES

    A - TRIPLOIDY

    B - TETRAPLOIDY

     


    Contributor(s)

    Written2000-08Jean-Loup Huret, Claude Leonard
    Genetics, Dept Medical Information, University of Poitiers, CHU Poitiers Hospital, F-86021 Poitiers France

    © Atlas of Genetics and Cytogenetics in Oncology and Haematology
    indexed on : Tue Mar 14 13:57:42 CET 2017


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