Genetic Counselling of a Case of Down Syndrome

Down syndrome is the most common chromosomal disorder, occurring with a frequency of 1:800 to 1:1000 newborns.
Genetic counseling relies fundamentally on obtaining a chromosomal analysis (karyotype) of the child to determine the exact etiology, which dictates recurrence risks.
Trisomy 21, caused primarily by meiotic nondisjunction, accounts for 95% of cases.
Chromosomal translocations (most commonly involving chromosomes 21 and 14) account for 4% to 5% of cases.
Chromosomal mosaicism accounts for approximately 1% of cases.

Parents of a child with Down syndrome should be counseled with tact, compassion, and truthfulness.
The physician should inform the parents about the disorder as early as possible after the diagnosis is clinically suspected and confirmed.
Counseling must be conducted in the presence of both parents in a private setting.
Information should be delivered in simple, positive language that provides hope, allowing sufficient time for parents to process the information and ask questions.
The explicit details of genetics and recurrence risk should only be discussed after a definitive chromosomal analysis is available.
Discussions regarding institutionalization and adoption should not be initiated unless asked by the parents, and both options should generally be discouraged.
Parents should be encouraged to contact local Down syndrome parent associations for community support.
Routine follow-up appointments should be scheduled to establish ongoing care.

The clinician must discuss known medical problems and associated comorbidities, emphasizing that routine screening will be implemented to manage these risks.
Common anomalies to outline include congenital heart disease (present in approximately 40% of cases), gastrointestinal atresias, hearing and vision defects, hypothyroidism, and an increased risk of leukemia.
It is crucial to highlight the importance of early intervention programs, including early stimulation, physiotherapy, occupational therapy, and speech therapy.
Parents must be informed about what children with Down syndrome can do, rather than focusing solely on intellectual disabilities and comorbidities.
Parents should be reassured that most children with Down syndrome are trainable, adjust very well socially, are highly affectionate, and many can be successfully employed in adulthood.

The risk of recurrence is heavily dependent on the maternal age and the specific cytogenetic cause identified via karyotyping.
The risk of nondisjunction trisomy 21 increases significantly with advancing maternal age: the risk is 1:1550 at 15–29 years, 1:800 at 30–34 years, 1:270 at 35–39 years, 1:100 at 40–44 years, and 1:50 after 45 years.
For women aged 35 years or younger who have had a child with nondisjunction trisomy 21, the recurrence risk in a subsequent pregnancy is approximately 1%.
If the mother is older than 35 years, the risk is only slightly increased over her baseline age-dependent frequency.
In cases of translocation, karyotyping of both parents is mandatory to determine if either parent is a balanced translocation carrier.
If the mother is a carrier of a balanced translocation, the recurrence risk is approximately 10%.
If the father is a carrier of a balanced translocation, the recurrence risk is 4% to 5%.
A parental balanced translocation involving two copies of chromosome 21, t(21q;21q), carries a 100% recurrence risk for Down syndrome in all viable fetuses.

Counseling must include information regarding options for prenatal screening and diagnosis in future pregnancies.
Maternal serum screening (PAPP-A and free hCG in the first trimester; alpha-fetoprotein, hCG, estriol, and inhibin A in the second trimester) and fetal ultrasonography (evaluating nuchal translucency and absent nasal bone) are effective non-invasive screening tools to assess risk.
Non-invasive prenatal screening (NIPS) using cell-free fetal DNA from maternal blood after 10 weeks of gestation is highly reliable with a negative predictive value of 98–99%.
Definitive prenatal diagnosis can be achieved via fetal karyotyping using chorionic villus sampling at 11–12 weeks of gestation or amniocentesis at 16–18 weeks.