Monday, November 9, 2009

- All you need about "Down´s syndrome".


English physician John Down first characterized Down
syndrome as a distinct form of mental disability in 1862 due to
his perception that children with Down syndrome shared physical
facial similarities (epicanthal folds) with those of Mongolian race.

  • In general population 1:660.
  • It is the most common Autosomal abnormalities.
  • It has equal sex distribution.
-Causes (cytogenic types):-

1-Complete Trisomy 21 (non disjunction):-

-Incidence:- 95%.

-Due to non-disjunction of chromosome 21 during meiotic division (

(i.e failure of a chromosome 21 pair to separate) so an ovum with

24 chromosomes when fertilized by a sperm carrying 23

lead to formation of a fertilized ovum with

47 chromosome.

-It occur during oogenesis more than spermatgenesis.

-The risk increases with age of the pregnant mother especially

over 40years as the primary oocytes of the mother have satyed in

the prophase for a long time ( 40 years or more).


47,xx+21(female down).

47,xy+21(male down).

(+ means that an extra chromosome is present).

(Non disjunction in mother)

2-Mosaic Down´s syndrome:-

-Incidence:- 1%.
-It is the best type.
-Due to non-disjunction of chromosome 21 occurig early in the
division of zygote (i.e after zygote formation) which results in
formation of two cell lines (normal & trisomic).

some cells as non-disjunction type & the other are normal.

-Clinical manifestaions are less than complete triosomy.

3-Translocation Down Syndrome:-

-Incidence:- 4%.
-Due to unbalanced translocation of chromosome 21 to another
chromosome in group D (usually chromosome 21) or to another
chromosome in group g resulting in phenotype same as trisomy 21
Down syndrome but genotype is 46 chromosome.

-It is the most serious type.

-Robertsonian translocations is the most common type.

-Clinical manifestaions:-

1-conatant features:-
  • Physical growth retardation.
  • Mild to moderate degrees of mental retardation.
  • Hypotonia.
  • Brachycephaly(flat occipit).
  • silky hair.
  • Microcephaly.
  • Wide anterior fontanel.
  • Delayed closure of posterior fontanel.
  • upward slanting eyes.
  • Medial epicanthal folds(extra skin folds at the medial
  • corners of the eyes).
  • narrow palpebral fissures.
  • Brushfield spots iris(speckled irises).
  • hypertelorism.
  • cataract.
  • small.
  • low set.
  • Backward displacment.
  • Short.
  • webbed.
  • small.
  • depressed nasal bridge.
  • Congenital HD(50%)
  • Most common(Av canal,VSD).
  • Protruded (small oral cavity).
  • fissured.
unilateral or bilateral absence of one rib.

  • Duodenal atresia.
  • Imperforate anus.
  • Umbilical hernia.
  • Congenital mega colon.
  • Distended abdomen(Due to hypotonia).
  • Diastasis recti.
  • Brachydactyle(short & stocky).
  • Clinodactyly i.e incurved little fingers(due to rudimentary or absent middle phalanx of little finger as it the last phalanx to develop).
  • Simian creases:- may be partial or complete.
  • Ridges hypoplasia.
  • Syndal gap (i.e wide space between the big toe & second toe).
  • syndal line(i.e deep planter crease).
  • Hypothyrodism(15%).
  • cryptorchidism.

- Complications:-
  • Accidents due to mental retardation.
  • Heart failure due to Congenital HD.
  • Recurrent Infections (chest,Otitis media,sinusitis) due to decrease immunity,hypotonia,aspiration.
  • They are liable to leukemia "20 times more than general population.
  • GIT complications.
  • Arrythmia which is the cause of sudden death.


(A)Prenatal diagnosis:-
  • Amniocentesis
  • chrionic villous sampling
  • Karyotyping
  • Triple test
(b)After birth:-
  • Karyotyping:- is dianostic.
  • For Cvs:-Echo,ECG.
  • For blood:CBC to exclude leukemia.
  • Baruim for GIT anomalies.
  • Radiology for U.T anomalies.
  • Thyroid function tests (T3,T4,TSH).


- Treatment of congenital anomalies & associated disorders.
- Social,educational& behavioral therapy in special institutes.


(1)Langman’s Medical Embryology 9th ed,ch1,p.g11.
(2)Priciples of histology vol1,staff members ,faculty of medicine,mansoura university,ch3,p.g72,73.
(3)Richard E Behrman,Nelson Textbook of Pediatrics,17th ed,Ch70,
(4)Down syndrome from Wikipedia,here

Return to list of medical syndromes here

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