Trisomy 8

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)

The trisomy 8 , also known as Warkany syndrome 2 (named after the pediatrician Joseph Warkany, 1902-1992), is a chromosomal feature based on a genome mutation in the genetic material of chromosome 8 triple in some or all cells of the body of man ( trisome ) instead of the usual double ( diploid ).

Usually there is a mosaic trisomy 8 in which only some of the cells have the additional chromosome and at the same time a cell line with the usual disomic chromosome set exists. This parallel presence of several karyotypes within an organism is called a mosaic in genetics . The karyotype of mosaic trisomy 8 is 46, XX / 47, XX, + 8 and 46, XY / 47, XY, + 8, respectively.

Free trisomy 8 , in which the additional chromosome 8 can be detected in all body cells ( karyotype : 47, XX, + 8 or 47, XY, + 8), is less common .

Frequency of occurrence

Trisomy 8 is one of the rare chromosome features. It occurs sporadically (sporadically, randomly), around 120 cases have been documented. Trisomy 8 is predominantly a mosaic (mosaic trisomy 8 / trisomy 8 mosaic syndrome ). Both boys and girls can be born with trisomy 8.

Common features before birth (prenatal)

In the course of the continuously developing possibilities of prenatal examinations ( prenatal diagnosis ), some peculiarities have been documented that can be found comparatively often in unborn babies with trisomy 8.

The signs that can indicate the presence of a trisomy 8 in the unborn child, especially in combination with one another, and which can sometimes be recognized by means of ultrasound examinations , include, for example:

Heart defect

Malformations of the kidneys , enlargement of the renal pelvis

Skeletal malformations ( tetramellia )

Bending of the spine with an outward curve to the front ( scoliosis , lordosis , kyphosis )

two or more consecutive vertebrae are completely or partially fused together ( block vertebrae )

slight bending of the little finger in the direction of the ring finger ( clinodactyly ) with simultaneous shortening of tendons and tendon sheaths, which make a complete extension of the respective finger impossible ( camptodactyly )

a comparatively small mouth - chin region ( mandibular retrognathy ) with a shortening of the lower jaw

Short fingers ( brachydactyly )

narrow iliac scoop

Absence or malformation of the kneecaps ( aplasia or hypoplasia of the patella)

Fluid accumulation in the neck area (high neck transparency )

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.

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. Particularly with the chorionic villus sampling, it must be taken into account that a mosaic trisomy 8 can also occur in the placenta , and the baby does not have a fetal mosaic in itself, or mosaics are not always recognized during the other chromosome examination.

Common postpartum features (postnatal)

After birth , most infants with trisomy 8 have different physical characteristics that make what is known as a suspected diagnosis possible. These include B .:

congenital joint stiffness ( arthrogryposis )

often spina bifida occulta

Special features of the soles of the feet (particularly noticeable grooves on the soles / plantar furrows)

a comparatively large distance between the first and second toe ( sandal gap / sandal furrow )

many and deep furrows in the palms of the hands ( palmar furrows )

Four-finger furrow (in approx. 75 out of 100 children)

comparatively deep, large and long ears

underdeveloped (hypoplastic) fold that lies opposite the rim of the auricle ( anthelix )

high forehead

short neck

narrow, sloping shoulders

long chest

Special features of the number and width of the ribs

surplus (accessory) nipples ( nipples )

high, narrow palate

Cleft palate

full, plump lips, everted lower lip

comparatively small eye relief ( hypotelorism )

One or both eyelids drooping , more often affecting the upper eyelid ( ptosis )

Squint ( strabismus )

broad nose , often upturned nostrils (nares)

often above average weight

increased tumor risk

mild to moderate cognitive disability

Other syndromes with arthrogryposis can be used as differential diagnoses .

course

Trisomy 8 cannot be cured, only the symptoms can be treated. The clinical picture is quite variable, especially with mosaic trisomy 8, and people are also known to have hardly any abnormalities.

A prognosis for physical development depends on which physical characteristics are present in which form and how they can be treated or how they are treated.

The cognitive impairments are generally classified as mild to moderate; in people with mosaic trisomy 8 they are often mild and very variable in severity. With a significantly lower proportion of trisomeric cells, it is also possible to achieve the usual intelligence .

literature

R. Witkowski, O. Prokop, E. Ullrich, G. Thiel: Lexicon of Syndromes and Malformations 7th edition. Springer, Berlin 2003, ISBN 3-540-44305-3 .
C. Danesio et al: Constitutional trisomy 8 mosaicism: Mechanism of prigin, phenotypic variability, and risk of malignancies. In: Am J Med genet. 1998; 80, p. 540.
A. Gotze et al.: Trisomy 8 Mosaicism in a with patient tetraamalie. In: Am J Med genet. 1999; 86, pp. 497-498.
A. Jay et al: A case report of mosaicism for partial trisomy 8: A case report including fetal pathology. In: Prenatal Diagnosis. 1999; 19, pp. 976-979.