Trisomy 9

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Classification according to ICD-10
Q92.0 Complete trisomy, meiotic nondisjunction
Q92.1 Complete trisomy, mosaic (mitotic nondisjunction)
Q92.2 Partial trisomy, major form

A whole arm or more doubled

Q92.3 Partial trisomy, minor form

Less than a whole arm doubled

Q92.4 Chromosome duplications that are only visible in the prometa phase
Q92.5 Chromosome duplications, with other complex rearrangements
ICD-10 online (WHO version 2019)

A trisomy 9 , i.e. a tripling of the genetic material of the 9th chromosome on the basis of a genome mutation , occurs comparatively rarely, usually in the mosaic form or as a partial trisomy 9 p (= Rethoré syndrome ) in the translocation form . The free trisomy 9 , wherein the all cells in chromosome 9 tripled present, typically results in the first third of pregnancy to a spontaneous miscarriage .

The first description in 1973 goes back to Feingold and Atkins.

Mosaic trisomy 9

In the mosaic trisomy 9 is not available in all body cells chromosome 9 triple ( trisom ) instead of two times ( disomic ) exists, but there is also a cell line with the usual set of chromosomes. The parallel presence of several karyotypes within an organism is called a mosaic in genetics . The karyotype of the mosaic trisomy 9 is therefore 46, XX / 47XX + 9 or 46, XY / 47XY + 9.

Partial trisomy 9p / Rethoré syndrome

This chromosomal peculiarity is usually present as a translocation form and is very rare. Since the first description of the syndrome in 1970 by the French geneticist Marie-Odile Rethoré, over 100 case studies are known. Apparently there is a familial accumulation if one of the parents has a so-called balanced translocation of the corresponding chromosome segment:

A balanced translocation occurs when an entire chromosome or a part of it attaches to another chromosome. However, this does not change the amount of genetic material. The genetic information is thus in balance despite the changed position.

People with Rethoré syndrome have a partial (= partial, proportional) tripling of chromosome 9: There is only a trisomy of the short arm of the 9th chromosome (9pter-q1), usually in connection with a translocation of the corresponding chromosome segment another chromosome.

Partial trisomy 9 (with or without translocation) can be diagnosed prenatally by means of an amniocentesis or chorionic villus sampling or the chromosome analysis with a special Locus probe that follows these examinations, or postnatally ( postnatally ) by examining the blood of the child concerned In most cases, the children die during pregnancy (usually in the very early stages) and the pregnancy ends with an often unnoticed miscarriage .

Symptoms

The presence of additional hereditary material due to a partial trisomy 9 p leads to various symptoms in people with Rethoré syndrome , although not all features or not all features are present in the same degree in a person. Some of the physical characteristics can already be recognized during ultrasound examinations as part of prenatal diagnostics . The most common features include:

However, none of these symptoms are conclusive enough for a clear diagnosis , even if some of the special features occur in combination with one another.

diagnosis

A diagnosis is still only possible by examining the chromosomes themselves. Prenatal methods in particular are amniocentesis or chorionic villus sampling or the chromosome analysis that follows these procedures.

As a differential diagnosis that come Patau Syndrome (Trisomy 13) Edwards syndrome (trisomy 18), the Wolf-Hirschhorn syndrome and triploidy in question.

Prognosis and therapy

No form of trisomy 9 is causally curable. A therapy is therefore possible only insofar as certain symptoms by medical - therapeutic can reduce or offset methods. So far, many children with trisomy 9 have died during pregnancy or a comparatively short time after birth . In children who live longer, a mosaic trisomy 9 can usually be found and, depending on the proportion of disomeric cells , the prognosis is often more favorable, although it also depends on which physical characteristics are present and how they can be treated or how they are treated become. The cognitive impairments are generally classified as severe.

See also

literature

  • R. Witkowski, O. Prokop, E. Ullrich, G. Thiel: Lexicon of Syndromes and Malformations 7th edition. Springer, Berlin 2003, ISBN 3-540-44305-3 .
  • RSJ Mc Duffie: Complete trisomy 9: case report with ultrasound findings. In: Am J Perinatol. 1994; 11, pp. 80-84.
  • A. Merino et al: Prenatal diagnosis of trisomy 9 mosaicism: Two new cases. In: Prenat Diagn. 1993; 13, pp. 1001-1007.
  • MG Pinette et al .: Prenatal diagnosis of nonmosaic trisomy 9 an relates ultrasound findings at 11.7 weeks. In: J Matern Fetal Med. 1998; 7, pp. 48-50.
  • MO Rethore et al .: Sur quatre cas de trisomie pour le bras court du chromosome 9. Individualisation d'une nouvelle entite morbide. In: Annales de Ginitique. 1970; 13, pp. 217-232.
  • R. Saura et al .: Prenatal diagnosis oft trisomy 9. Six cases an review of the new literature In: Prenat Diagn. 1995; 15, pp. 609-614.
  • Ulla Schmidt: Johanna. A mother's memories of the journey with her very disabled child. 1992, ISBN 3-88617-017-9 . (Experience report in the form of poems and thoughts / diagnosis: partial trisomy 9 or 18 )