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Down Syndrome (Trisomy 21) - Hydramnios ; complex malformations ; pyelectasis ; duodenal atresia.

Dr Sampurna Roy MD   


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 1) Hydramnios           2) Duodenal atresia              3) Pyelectasis


Down syndrome is the most common chromosomal disorder.

Eight important signs of Down syndrome is described:

(1) Abundant neck skin,

(2) Mouth corners turned downward,

(3) General hypotonia

(4) Flat face

(5) Dysplastic ear

(6) Epicanthic eye-fold

(7) Gap between first and second toes

(8) Protruding tongue

Important Antenatal markers for the diagnosis of fetuses with Trisomy 21 :

Ultrasound examination may show hydramnios (polyhydramnios), duodenal atresia and pyelectasis (dilatation of renal pelvis) 


Clinical feature:

- Flat facies with oblique palpebral fissures and epicanthic folds.

Nasal bone and nuchal fold are efficient markers for Down syndrome.

Absent nasal bone was a better predictor of Down syndrome, compared with nuchal fold, and should be a standard marker when a second-trimester genetic sonogram is performed.

According to recent study intelligence based on facial appearance are unreliable even in groups characterized by a genetic disorder such as Trisomy 21.

- The protruding tongue is large and wrinkled  

- Severe mental retardation. The intelligence quotient (IQ) in most cases is lower than 50.

- Hands are broad and short and show transverse simian crease.     


  Diagram of hand showing prominent transverse simian crease

-  Feet : There is a gap between the first and second toe in Down Syndrome - see the diagram below.


- Congenital heart disease, especially septal defects, responsible for the majority of deaths in infancy and childhood.

Cardiac defects include endocardial cushion, including ostium primum, atrial septal defect, atrioventricular valve formation.

Visit: Cardiac Path Online


Diagram of Heart in Down Syndrome

- 10 to 20-fold increased risk of developing acute leukemia.

Both acute lymphoblastic leukemias and acute non-lymphoblastic leukemias occur.

Megakaryocytic proliferative disorders are more common in patients with Down's syndrome.

The spectrum of myeloproliferative disorders including myelofibrosis, myeloid metaplasia, and megakaryoblastic leukemia is seen in these patients.


 Bone marrow

- Sub-clinical hypothyroidism was the most common thyroid abnormality in children with Down's syndrome.

A timely-scheduled evaluation of thyroid function is needed to establish the natural course of this abnormality and the proper management guideline.



- Premature Alzheimer disease in those who survive after 35 years of age.


 Diagram of the brain 

- There is serious infections resulting from abnormal immune responses. Lung infection is common.

  Lung infection 

- The arthropathy of Down syndrome is an underrecognized condition that results in chronic disability and functional impairment in a population already at significant risk.

Children with Down syndrome are predisposed to autoimmune disorders, but arthritis is overlooked in surveillance guidelines.

To maximize joint function and quality of life, providers caring for children with Down syndrome need a high index of suspicion for the related arthropathy.



- Ocular problems as refractive errors, strabismus, accommodation, and cataract are well known in children with Down syndrome.

Other findings include nystagmus, Brushfield spots, lens opacities  abnormalities of the retinal vessels, foveal hypoplasia, or retinal pigment epithelium hyperplasia and optic disc pallor. 


 Slanted eyes, epicanthic folds and brushfield spots are characteristic features of the eye in Down syndrome.


Karyotypic features:

-  About 95% have a complete extra chromosome 21 (47, XY, +21).

The incidence of this form is strongly influenced by maternal age (1 in 1550 births in women younger than 20 years, increasing to 1 in 25 in women older than 45 years). In 95% of these cases, the extra chromosome is maternal in origin.

-  A translocation variant, making up 4% of all cases, has extra chromosomal material derived from inheritance of a  parental chromosome bearing a translocation of the long arm of chromosome 21 to chromosome 22 or 14 (Example: 46,XX,der(14, 21) (q10,q10), +21.

Because the fertilized ovum already possesses two normal autosomes 21, the translocated chromosomal fragment  provides the same triple-gene damage as trisomy 21.

Such cases are frequently (but not always) familial because the parent is a carrier of a robertsonian translocation. 

Such a rearrangement may also occur during gametogenesis.

- Mosaic variants make up about 1% of all cases, they have a mixture of cells with normal chromosome number and cells with extra chromosome 21.

It is recommended that any patient with confirmed hydramnios have a detailed ultrasound examination with special attention paid to the heart, face, and hands.


Further reading:

Misleading face-based judgment of cognitive level in intellectual disability: The case of trisomy 21 (Down syndrome).

A de novo duplication of chromosome 21q22.11→qter associated with Down syndrome: prenatal diagnosis, molecular cytogenetic characterization and fetal ultrasound findings.

Esophageal and duodenal atresia in a fetus with Down's syndrome: prenatal sonographic features.

Antenatally detectable markers for the diagnosis of autosomally trisomic fetuses in at-risk pregnancies.

Prognosis and management of acute myeloid leukemia in patients with Down syndrome.

A score based on eight signs in the diagnosis of Down syndrome in the newborn.


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Dr  Sampurna Roy  MD

Consultant Histopathologist (Kolkata - India)







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