Down Syndrome: How often it occurs, signs to watch out for, couples chance of having a child with it, management

Down syndrome is one of the most common chromosomal condition causing intellectual disability and it was named after British physician Dr John Langdon Down who described this syndrome. Normally a person has 46 chromosomes in each cell but a person with down syndrome will have 47 chromosomes as they have an extra copy in 21st chromosome, hence the name Trisomy 21.

In an interview with HT Lifestyle, Dr Vignesh Kumar S, MD (Paediatrics), DM (Neonatology) at Cloudnine Group of Hospitals in Chennai's T Nagar, answered some prominent questions about Down syndrome:

• How often does Down syndrome occur?

Prevalence is 1:800 live births worldwide.

• What is the cause for Down syndrome?

95% of cases of downs syndrome is caused by an error in cell division. Other few cases are due to translocation and mosaicism. Each human cell contains 46 chromosomes but in individuals with downs syndrome each or some cells contains an extra copy of chromosome 21. This additional chromosome is responsible for physical and developmental features of Down syndrome.

Three categories of Down syndrome are:

1. Trisomy 21: Most common type (95%).Each cell has 47 chromosomes. Occurs due to error in cell division. Risk increases with advanced maternal age.
2. Translocation: Constitutes 3-4 % of cases. Extra chromosomes attaches to another chromosome, commonest being chromosome 14 or 21.
3. Mosaicism: constitutes 1-2%, rare variant. some cells have normal chromosomes (46) and few cells have 47 chromosomes. Patients have milder phenotype.

• What are features to identify Down syndrome?

Hall mark features of Down syndrome are

1. Flat facies
2. Upward slanted palpebral fissure
3. Small dysplastic ears
4. Increased flexibility of joints
5. Short neck
6. Short 5th digit
7. Single transverse palmar crease
8. Pelvic dysplasia
9. Less muscle tone.

• How to diagnose Down syndrome?

1. Post natal diagnosis: It’s mainly a clinical diagnosis, however Karyotyping remains gold standard that detects extra copy of chromosome 21. Results are available in 2-3 days. Rapid diagnosis is possible with quantitative fluorescent polymerase chain reaction (QF PCR) or Fluorescent in situ hybridization technique (FISH). Results are available within 2 days.
2. Antenatal screening and diagnosis: Antenatal screening can be done during first or second trimester. First trimester screening includes maternal age, nuchal translucency assessment by ultrasound, beta-hCG levels, PAPP-A levels between 11 and 13 weeks. Second trimester screening includes quadruple test (Beta-Hcg, Alphafetoprotein, Unconjugated estriol, Inhibin A. If the risk of down syndrome exceeds cut off of 1:250,we can proceed with chorionic villous sampling at 11-12 weeks or amniocentesis at 16-18 weeks.

• What type of problems would Down syndrome children typically have?

Variable degree of developmental delay is common feature in all patients with Down syndrome. Majority will have an intelligent Quotient (IQ) in mild (50-70) to moderate range (35-50). Children with Down syndrome will have difficulty in feeding, toilet training & sleep pattern at all ages compared to normal children. They have poor language &communication skills. Down syndrome patients have a pleasant behaviour, caring, affectionate and quite social. Many patients with Down syndrome have autistic features. Majority of patients with Down syndrome have features of Alzheimer disease by 40 years of age.

1. Most common problem is heart defects which constitutes 40-50%.all children with downs syndrome should be checked by paediatric cardiologist for echocardiogram. some defects are minor and some may require surgery.
2. Around 10% of children with downs syndrome have intestinal malformations requiring surgery.
3. Children with Down syndrome can have hearing or visual impairment. So regular hearing and vision examination is necessary for children with downs syndrome.
4. They are at risk of thyroid problems and cancer (Leukemia).They should have regular check up with routine immunization.

• How severe is the mental retardation in children with Down syndrome?

The degree of mental retardation ranges from mild to moderate to severe. Most of children with downs syndrome falls within mild to moderate mental retardation.

• Management of children with Down syndrome?

A multidisciplinary team involving Paediatrician, Developmental specialist, Psychologist, Neurologist, cardiologist, Ophthalmologist, ENT specialist, Speech therapist, Physical and occupational therapist is essential in management of child with Down syndrome. Following measures helps children with Down syndrome to live a healthy, happy and independent life:

1. Early stimulation to improve developmental skills
2. Providing home environment
3. Providing parental care
4. Health education
5. Forming parent support groups for sharing their experience
6. Vocational training of children
7. Availability of specialised medical care when needed

• What are couples chances of having a child with Down syndrome?

Any couple having chances of downs syndrome child depends on age of mother. If mothers age is 35 years, odds of having a child with Down syndrome is 1:350, if mother age is less than 25 years, risk is 1:1400 and if mother age is 40 years the odd is 1:100.

• What is risk of a parent of a child with downs syndrome having another child with downs syndrome?

If the first child is having downs syndrome, chances of couple having another child with downs syndrome is 1:100. The chances for a child with Down syndrome increases with maternal age.

• Can people with Down syndrome have children?

Miscarriage rate and infertility rate is increased in women with Down syndrome but it is still possible for them to have children. The likely hood of having a child with downs syndrome is approximately 50%.

• Life expectancy of a person with Down syndrome?

Life expectancy is beyond 60 years over last few decades with good quality medical care and early identification & treatment of complications.

• Are there any organisations for persons with downs syndrome?

National downs syndrome society (NDSS) is the leading human rights organization for all individuals with downs syndrome. Down syndrome federation of India (DSFI) is a parent support group started by Dr Surekha Ramachandran to help people with downs syndrome and their families to lead a more normal life.

• Why is it important to get involved in a support group?

Support group allows opportunity to get resources and questions answered by people that are in similar situations. There is nothing better than being surrounded by people who understand what you are going through.