Clinical Cytogenetics and Syndromes

What physical features are commonly seen in patients with Down syndrome?

What percentage of spontaneous abortions have a demonstrable chromosomal abnormality?

What is the term for the phenomenon where chromosomally abnormal conceptuses are eliminated through abortion during pregnancy?

Which of the following syndromes has the highest rate of biological elimination?

What is the relationship between chromosome number and degree of biological elimination?

What is the approximate percentage of conceptuses with chromosomal abnormalities that are born alive?

What is the primary application of clinical cytogenetics?

In which of the following individuals can cytogenetic abnormalities be found?

What is the primary goal of prenatal cytogenetics?

What is the characteristic of a syndrome in clinical cytogenetics?

What is the significance of childhood and adult cytogenetics?

What is the primary advantage of clinical cytogenetics?

Clinical Cytogenetics

Cytogenetic abnormalities can be found in: • Apparently normal individuals • Patients with phenotypic anomalies (e.g. cleft lip/palate) • Patients with diagnosed genetic disorders
Diagnosis of cytogenetic disorders can be made at any stage of life: • Prenatal cytogenetics: genetic abnormalities diagnosed before birth • Postnatal cytogenetics: evidence of cytogenetic abnormalities sought after birth • Childhood and adult cytogenetics: genetic abnormalities manifest later in life

Syndromes

A syndrome is established when the same set of features are seen in several unrelated individuals, assumed to have a common basis of specific chromosomal abnormalities
These syndromes may occur in different degrees (mild, moderate, or severe manifestations)
Example: Down syndrome • Characterized by flat bridge of nose, slanted eyes, prominent palpebral fissures • Patients have intellectual disabilities and cardiovascular defects

Prenatal Cytogenetics

50%-60% of spontaneous abortions (miscarriages) during early pregnancy have a demonstrable chromosomal abnormality
52% of these are autosomal trisomies
1 in 3 conceptuses have chromosomal abnormality, but only 6:1000 live births due to biological elimination of recognized errors
Rate of biological elimination: • 95% of 45, X (Turner's Syndrome) • 90% of Trisomy 13 (Patau Syndrome) • 80% of Trisomy 18 (Edwards Syndrome) • 65% of Trisomy 21 (Down syndrome)
Biological elimination is inversely proportional to chromosome number, while survival is directly proportional

This quiz covers the basics of clinical cytogenetics, including cytogenetic abnormalities, diagnosis, and syndromes. Learn about prenatal cytogenetics, chromosomal abnormalities, and specific syndromes like Down syndrome.