Trisomy 13 is also known as patau syndrome. it is a genetic condition arising due to presence of an extra copy of chromosome 13. The manifestation of this condition include Cardiac anomalies Defect in nervous system Hypotonia or weaker Muscle Tone Deformities in physical feature and Intellectual abilities.
The survival rate of such affected individual is very low due to multiple serious abnormality is and effect and most children fail to live beyond few weeks or months. The occurrence of trisomy 13 is just one in about 16000 cases and the chances increases fairly with the maternal age. The extra genetic material may be present in form of a complete chromosome 13 that is 3 copies of chromosome 13 at present. In such cases the similarity of anomalies is high, lowering the chances of survival of affected individual.
In mosaic condition and extra copy of chromosome 13 is present only in few cells of the body and not all therefore its effect are less severe.
If the extra genetic material chromosome 13 gets translocated to another chromosome, it is called translocation trisomy 13.This usually happens during gamete formation or sometime during the early stages of embryo development.Translocation trisomy 13 is inheritable a parent with a balanced translocation is a potential career and is likely to produce a child with trisomy 13.
In 1966 class patau and his Associates observed and Infant with cross developmental malformation with the karyotype of 47 chromosomes.
The additional chromosome was medium-sized, one of acrocentric D group.The G and Q Banding techniques have identify the extra D chromosomes as number 13.
The trisomy 13 condition has since been described in many newborns and is called Patau syndrome,Being designated as 47,13 +.
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70% of the trisomy 13 cases are caused by meiotic nondisjunction ;10% of the cases are trisomic mosaics; and 20 % are partially trisomic due ti translocation.
As a chromosome 13 contains considerable active genetic material most chromosome 13 trisomies abort.Of those that are life born 90% die during the first year of life.Those few that survived beyond the age of 2 years of a from severe mental retardation.
The characteristics of trisomy 13 include
- Seizures
- Moderate Microcephaly ( small head )
- Wide space Eyes
- Beaked nose
- Cleft of the lips and palate
- low set ears
- Scalp defects
- And Characteristic ‘trigger thumb’ (the thumb and index fingers overlap the third finger).
Trisomy 13 baby display simian crease (one continuous crease across the palm of the hand ),as in down syndrome, As well as polydactyly (extra fingers and toes) ‚congenital heart disease, kidney disorders and malformed genitalia.
The average maternal and paternal ages of parents of affected infants are higher than the ages of parents of normal children , But paternal ages are not as high as the average maternal age as in case of down syndrome.
Both male and female parent have average about 32 years of age when the affected child is born. because the condition is so rare, it is not known as the origin of the extra chromosome is more of a maternal and paternal arises equally from other parents.