15 Questions
What is the average life span of an individual with a specific genetic condition?
25yrs. To 50 yrs.
What is the mortality risk if the mother is a carrier of 14q:21q translocation?
10-15%
What is the most common cause of death in older children with a certain condition?
Accidents due to MR
What is the mortality risk if the mother is a carrier of 21q:21q translocation?
100%
Why has there been an improvement in survival rates for individuals with a certain condition?
Increased placements of infants in rehabilitation homes and changes in treatment for common causes of death.
What is the genetic basis of Down syndrome, and who is it named after?
Down syndrome is caused by the presence of all, or part of a third copy of chromosome 21, and it is named after physician John Down.
What is the incidence of Down syndrome in the general population, and what is the most common genetic type?
The incidence of Down syndrome is 1/600 - 1/800 births, and the most common genetic type is nondisjunction (trisomy 21), accounting for 95% of cases.
What is the effect of advancing maternal age on the risk of Down syndrome?
Advancing maternal age, typically above 35, increases the risk of Down syndrome.
What is the characteristic feature of translocation of chromosome 21 in Down syndrome?
Translocation of chromosome 21 involves the breaking and attaching of chromosome 21 to other chromosomes (usually 14) during cell division, resulting in a functional trisomy 21.
What is the difference between mosaicism and nondisjunction in Down syndrome?
Nondisjunction occurs during meiosis, resulting in a zygote with 3 copies of chromosome 21, while mosaicism occurs after zygote formation, resulting in two cell lines (normal and trisomic).
What are the characteristic physical features associated with Down syndrome?
Down syndrome is typically associated with physical growth delays and characteristic facial features.
What is the relationship between Down syndrome and intellectual disability?
Down syndrome is associated with mild to moderate intellectual disability.
What is the significance of trisomic mothers in the context of Down syndrome?
Trisomic mothers have a higher risk of having a child with Down syndrome.
What is the impact of Down syndrome on an individual's developmental milestones?
Down syndrome is associated with physical growth delays and developmental delays.
What types of health complications are associated with Down syndrome?
Down syndrome is associated with an increased risk of various health complications, including physical growth delays and intellectual disability.
Study Notes
Down Syndrome
- Parents who are carriers of the genetic translocation for Down syndrome have a higher risk of having a child with the condition.
Clinical Features
- Mental retardation, hypotonia, and delayed developmental milestones
- Craniofacial features: fine silky hair, mild microcephaly, flat occiput, small dysplastic ears, upward slanting palpebral fissures, epicanthic folds, and speckled irides (Brushfield spots)
- Small nose, flat nasal bridge, protruding tongue, open mouth, and high-arched palate
- Hand and feet features: simian crease, short and broad hands, hypoplasia of middle phalanx of 5th finger, and gap between 1st and 2nd toes
Health-related Problems
- Cardiovascular problems (50%): AVSD, VSD, ASD, and PDA
- Endocrine problems (1-4%): congenital or acquired hypothyroidism, diabetes mellitus
- Gastrointestinal problems (5%): duodenal, esophageal, and anal atresia, Hirschprung's disease, and celiac disease
- Haematological problems: acute leukemia, transient myeloproliferative disease
- Neurological problems: epilepsy, severe behavioral problems, Alzheimer's disease, memory problems, and autism
Management
- Eye exam should be performed in the newborn period or at least before 6 months of age to detect strabismus, nystagmus, and cataracts
- Thyroid function tests should be done in the newborn period and repeated at 6 and 12 months, and then annually
- Celiac disease screening should begin at 2 years and repeated if signs develop
- Hematology: CBC with DLC at birth to evaluate for leukemia
- Atlanto-axial instability: X-ray at 3 to 5 years of age
- Alzheimer's disease: adult with Down syndrome has an earlier onset of symptoms
Counseling
- Recurrence risk: 1-4% for trisomy 21, increased by 1% to maternal age-related risk
- New translocation (mutation): random risk as the general population
- If the mother is a carrier of 14q:21q translocation (45 xx): 10-15% recurrence risk
- If the mother is a carrier of 21q:21q translocation (45 xx): 100% recurrence risk
Mortality
- Average life span: 25-50 years
- Most likely cause of death: CHD, recurrent infections (in infancy), accidents due to mental retardation (in older children), atlanto-axial instability, and leukemia
- Improved survival due to increased placements of infants in rehabilitation homes and changes in treatment for common causes of death
- Survival is better for males
Down Syndrome
- Also known as "trisomy 21", a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.
- Typically associated with physical growth delays, characteristic facial features, and mild to moderate intellectual disability.
Clinical Features
- Mental retardation
- Hypotonia
- Delayed developmental milestones
- Cranio-facial features:
- Fine silky hair
- Mild microcephaly
- Flat occiput
- Small dysplastic ears
- Upward slanting palpebral fissures
- Epicanthic folds
- Speckled irides (Brushfield spots)
- Hands and feet:
- Simian crease
- Short, broad hands
- Hypoplasia of middle phalanx of 5th finger
- Gap between 1st and 2nd toes
Health-Related Problems
- Cardiovascular problems (50% of DS): AVSD, VSD, ASD, and PDA
- Endocrine problems:
- Thyroid problems (1% congenital, 4% acquired hypothyroidism)
- Diabetes mellitus
- Gastrointestinal problems (5%):
- Duodenal, esophageal, and anal atresia
- Hirschsprung's disease
- Celiac disease
- Haematological problems:
- Acute leukemia
- Transient myeloproliferative disease
- Neurological problems:
- Epilepsy
- Severe behavioral problems
- Alzheimer's
- Memory problems
- Autism
- Sleep problems:
- Sleep apnoea
- Other sleep disturbances
- Skeletal problems:
- Flat foot
- Atlantoaxial subluxation
- Visual problems:
- Refractive disorder
- Squint
- Nystagmus
- Cataract
- Hearing problems:
- Hearing loss
- Conductive hearing loss
- Chronic otitis media
Feeding Problems
- Chocking with feeds
- Recurrent pneumonia
- Unexplained failure to thrive (celiac disease)
- Constipation:
- Restricted diet
- Decreased fluid intake
- Hypotonia
- Hypothyroidism
- Hirschsprung disease
Reproduction
- Women with DS are fertile and may become pregnant
Incidence and Genetic Types
- Incidence in the general population: 1/600 - 1/800 births
- Genetic types of DS:
- Nondisjunction (trisomy 21): 95%
- Translocation of chromosome 21: 4%
- Mosaicism: 1%
Risk Factors
- Advancing maternal age (usually women of age 35 and above)
- Trisomic mothers
This quiz covers the clinical features of Down syndrome, including mental retardation, hypotonia, and delayed developmental milestones. It also explores the physical characteristics of the condition.
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