50–70% of cases are due to prenatal factors, 10–20% to perinatal and another 5–10% to postnatal factors
c. Children with Down syndrome have characteristic facies and habitus
d. Learning disability is evident before the age of 1 year
a. It is the most common genetic cause of learning disability
b. It is due to trisomy of chromosome 21
e. IQ in adults is usually less than 50
Patau syndrome is due to trisomy of chromosome 13. Children with Patau syndrome have abnormal genitalia and low IQ. It can be caused by other malfunctions like translocation.
Children with the syndrome may have rocker-bottom feet
Children with the syndrome have normal genitalia
It is caused only by non-disjunction of chromosomes during meiosis
IQ is usually normal
It is due to trisomy of chromosome 17
The most common cause of Down syndrome is trisomy 21 (more than 95% of cases). Only less than 5% is due to a Robertsonian translocation. The incidence per 1000 live births increases greatly from 5 in women under 35 to 25 in women under 40 years, but because of the higher number of pregnancies in younger women, most children with Down syndrome are born to mothers under the age of 35 years.
Incidence per 1000 live births increases for women over 35
Raised IgM and IgG levels are features
Most children with Down syndrome are born to mothers under the age of 35
The usual genetic cause is a Robertsonian translocation
About half of people with Down syndrome have congenital heart defects
Learning disability in a baby can be caused by the mother suffering from one of the following illnesses: non-infectious causes are diabetes, hypothyroidism, hypertension and malnutrition; infectious causes include syphilis, HIV and TORCH (toxoplasmosis, rubella, cytomegalovirus, herpes simplex) (rubella is German measles)
Down syndrome patients have an increased risk of Alzheimer’s dementia, hypothyroidism (20%), depression (10%), myopia (30%) and brachycephaly.
Features of Prader – Willi syndrome include short stature, hypogenitalism (cryptorchidism, micropenis, amenorrhoea), overeating, obesity, mild to moderate learning disability and sleep disorders.
Mild to moderate learning disability
Angelman (happy puppet) syndrome features ataxia, epilepsy (86%), paroxysms of laughter, microcephaly, prominent jaw and severe or profound learning disability.
Paroxysms of crying
IQ must be 70 or below, onset before 18, Deficit in adaptive functioning in at least 2 areas: ADL's, academic, work, leasure, health, safety. May have a mental illness.
IQ below 60
Absence of a mental illness
Onset before age 18 years
Onset before age 12 years
Deficit in at least one area of adaptive functioning
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