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

-History:-

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.

-Incidence:-

• 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

chromosomes 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).

-Karyotyping:-

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).

-Karyotyping:-
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.

2-Head:-

• Brachycephaly(flat occipit).
• silky hair.
• Microcephaly.
• Wide anterior fontanel.
• Delayed closure of posterior fontanel.

3-Eye:-

• 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.

4-Ears:-

• small.
• low set.
• Backward displacment.

5-Neck:-

• Short.
• webbed.

6-Nose:-

• small.
• depressed nasal bridge.

7-Heart:-

• Congenital HD(50%)
• Most common(Av canal,VSD).

8-Tongue:-

• Protruded (small oral cavity).
• fissured.

9-Ribs:-
unilateral or bilateral absence of one rib.

10-Abdomen:-

• Duodenal atresia.
• Imperforate anus.
• Umbilical hernia.
• Congenital mega colon.
• Distended abdomen(Due to hypotonia).
• Diastasis recti.

11-Hands:-

• 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.

12-Foot:-

• Syndal gap (i.e wide space between the big toe & second toe).
• syndal line(i.e deep planter crease).

13-Others:-

• 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.

-Investigations:-

(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:-

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


*References:-

(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,
(http://www.elsevier.com).
(4)Down syndrome from Wikipedia,here

Return to list of medical syndromes here