Questions and Answers
What is a common behavioral characteristic of children with Angelman syndrome?
Which syndrome is primarily associated with obesity due to extreme overeating and hoarding behaviors?
What genetic abnormality is associated with both Prader-Willi and Angelman syndromes?
What distinguishes the outcomes of genetic material absence from the mother versus the father in these syndromes?
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Children with Angelman syndrome are typically expected to have which level of intellectual disability?
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What is the estimated occurrence rate of fetal alcohol syndrome among live births?
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In terms of prenatal alcohol exposure, what time period is considered especially harmful?
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Fetal alcohol syndrome is mainly characterized by which of the following features?
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Which population groups have a higher incidence of fetal alcohol syndrome compared to majority populations?
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What is believed to be a contributing mechanism for the abnormalities seen in fetal alcohol spectrum disorders?
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Study Notes
Chromosomal Basis of Intellectual Disabilities
- Down syndrome's chromosomal cause is linked to chromosome 21, but the definitive cause of intellectual disability remains unclear.
- Gene mapping indicates that specific genes may influence brain development, which could contribute to learning and language acquisition difficulties.
- Differences in hippocampal function have been observed, as the hippocampus is crucial for long-term memory, affecting language skill development in children with Down syndrome.
Fragile-X Syndrome
- Fragile-X syndrome is the most prevalent inherited intellectual disability, affecting approximately 1 in 4,000 males and 1 in 8,000 females.
- Physical characteristics can include a large forehead, prominent jaw, and low, protruding ears, although these features are more subtle than those seen in Down syndrome.
- Intellectual disability severity ranges from mild to moderate; some individuals may be profoundly affected while others may have normal intelligence.
- Males are more severely impacted than females, with most males exhibiting intellectual disability compared to about half of females.
Prader-Willi Syndrome
- Prader-Willi syndrome is a rare genetic disorder affecting 5 to 10 per 100,000 births, characterized by short stature, learning disabilities, incomplete sexual development, low muscle tone, and an insatiable urge to eat.
- Children typically develop severe overeating behaviors between ages 2 to 6, leading to obesity due to lower caloric needs relative to size.
Angelman Syndrome
- Angelman syndrome is associated with moderate to severe intellectual disability, characterized by ataxia, jerky movements, hand-flapping, seizures, and an absence of speech.
- Distinctive facial features include a large jaw and an open-mouthed expression.
Genetic Characteristics
- Both Prader-Willi and Angelman syndromes involve abnormalities on chromosome 15 but are spontaneous genetic defects rather than inherited conditions.
- The dysfunction is due to non-expression of genes on the affected mother's chromosome 15, leading to phenotypic variations based on whether the absent genetic material is maternal or paternal.
- There is ongoing research into the genetic factors influencing intelligence and adaptive abilities, highlighting the complexity of accounting for variations in phenotypic expression.
Inborn Errors of Metabolism
- Genetically based metabolic defects lead to inborn errors of metabolism, causing imbalances of essential chemicals during development.
- These errors account for 3% to 7% of severe intellectual disability cases.
Phenylketonuria (PKU)
- PKU is a well-known single-gene disorder occurring in roughly 1 in 15,000 individuals.
- The condition results from a recessive gene passed from both parents, leading to a lack of liver enzymes needed to convert phenylalanine into tyrosine.
- Accumulation of phenylalanine leads to brain damage, intellectual disability, musty body odor, hyperactivity, seizures, and dry skin and hair.
Risk Factors for Intellectual Disability
- Pregnancy and delivery complications contribute to about 10% of intellectual disabilities.
- General medical conditions during infancy and childhood, like infections and accidental poisonings, account for around 5% of cases.
Fetal Alcohol Spectrum Disorder (FASD)
- FASD is the leading preventable cause of intellectual disability related to prenatal alcohol consumption.
- Even minimal alcohol intake can adversely affect fetal growth and cognitive abilities, particularly during the first trimester.
- The most severe form, fetal alcohol syndrome, is linked to significant intellectual impairment and occurs in 0.5 to 2.0 per 1,000 live births, though it may be underdiagnosed.
Demographic Disparities
- Fetal alcohol syndrome incidence is notably higher among African Americans (4 times) and Native Americans (16 times) compared to the majority population.
Ongoing Public Health Challenges
- Public health campaigns advocating for abstinence from alcohol during pregnancy haven't led to a decrease in FASD incidences.
- Key features of fetal alcohol syndrome include central nervous system dysfunction, distinct facial abnormalities, and growth retardation, with affected children often below the 10th percentile in growth measures.
- The physiological mechanisms behind these abnormalities are not fully understood but involve both teratogenic effects of alcohol and associated nutritional issues from alcoholism.
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Description
Explore the chromosomal underpinnings of intellectual disabilities, particularly focusing on Down syndrome and chromosome 21. Delve into gene mapping that highlights how specific genes may influence brain development and learning abilities, including language acquisition. This quiz will guide you through the complexities of how hippocampal function affects memory and language skills in affected individuals.
