down’s syndrome2

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DOWNS SYNDROME


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Clinical features Down syndrome symptoms vary from

person to person and can range frommild to severe.

most likely to be diagnosed in thenewborn period as majority of themhypotonia and they have a widely

recognized appearance.


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Typical craniofacialappearance

Round face Flat nasal bridge Upslanted palpebral

fissures Wide epicanthic fold Brushfield spots in iris

(pigmented spots) Small mouth and

protruding tongue Low set/small ears Flat occiput and third

fontanelle


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Other anomalies Short neck Single palmar creases, incurved 5 th

finger Wide sandal gap between toes


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Newborn Cardiac defect (50%): AVSD most

common, VSD, ASD, TOF or PDA GIT (12%) duodenal atresia(commonest),

tracheoesophageal fistula, anorectal

malformation, pyloric stenosis orHirshsprung disease Vision : congenital cataracts(3%),

glaucoma Hypotonia & joint laxity Feeding problems Congenital hypothyroidism (1%) Congenital dislocation of hips Genitourinary tract - Renal malformations,

hypospadias, micropenis, cryptorchidism


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Infancy and childhood Delayed developmental milestone Mild to moderate intellectual impairment (IQ 25-50) Seizure disorder (6%) Recurrent respiratory tract infections Hearing loss (>60%) d/t secretory otitis media,

sensorineural deafness or both Visual impairment : squint (50%), cataract (3%), nystagmus

(35%), glaucoma, refractive errors(70%) Sleep related airway obstruction Leukemia (1%)

Atlantoaxial instability Hypothyroidism(10%) Short stature Over/underweight Neurobehavioural disorders: ADHD, autism spectrum

disorders


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Adolescence & adulthood Puberty

In girls menarche is only slightlydelayed. Fertility persumed

In boys are usually infertile d/t lowtestosterone

Increased risk of dementia &Alzheimer in adult life

Shorter life expectancy


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Cytogenetic Extra chromosome 21 may result

from Non disjunction (94%) Translocation (5%) Mosaicism (1%)


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Non disjunction


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Error at meiosis The pair of chromosome 21s fails to

separate, so one gamete has twochromosome 21s and one has none.

Parentral chromosomes do not needto be examined

Incidence related to maternal age(increase in advanced maternal age)


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Translocation


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Extra chromosome 21 is joined ontoanother chromosome (usuallychromosome 14) known as anunbalanced Robertsoniantranslocation.

Parentral chromosomal analysis isessential since 25% of cases, one of the parents carries a balancedtranslocation(carrier).


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Risk of recurrence Risk of recurrence is 10-15% if

mother is the translocation carrier,2.5% if father is the carrier

If a parents carries the rare 21:21translocation, all the offspring willhave DS

If neither parents carries atranslocation, risk of recurrence is


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Mosaicism


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Arises after formation of zygote, bynon disjunction at mitosis

Some of cells are normal and somehave trisomy 21.

Milder phenotype


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Cytogenetic diagnosis is importantfor confirmation of the clinicaldiagnosis and, importantly, todetermine the risk of inheritance andrecurrence, thereby helping inparental genetic counselling


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Prognosis 85% of infants with trisomy 21

survive to 1 year of age Severe congenital heart disease is a

major cause of early mortality 50% of affected individuals live

longer than 50 years

down’s syndrome2

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