Teratology Lecture 1: History of Conjoined Twins

History of Teratology

• Conjoined twins have been reported to exhibit functional and emotional behavior, with cases showing differences in emotions, affections, and appetites.
• Thompson (1930) reported a case of dicephalic twins that showed emotional dissociation, where one head would cry while the other laughed, and one would eat while the other slept.

Conjoined Twins

• Craniopagus twins are rare, with an estimated occurrence of 1 in 3,000,000 births, or 1 in 58 conjoined twins.
• Types of conjoined twins include frontal, parietal, and occipital unions.
• Historical cases of conjoined twins include the twin girls born in 1495 in Worms, Germany, who were united by their foreheads.

Single Malformations

• Historical illustrations of single malformations include a tricephalic creature, a fetus with one phocomelic arm, a man with reduction malformation, an epigastric parasite, and a man with a defect of the anterior abdominal wall.

Biological Theories

• Aristotle (1943) had knowledge of teratologic facts, including redundance and reduction of fingers, toes, hands, and feet, as well as imperforate anus, and absence of the gallbladder, spleen, or kidney.
• Reduction malformations, osteogenesis imperfecta, and kleeblattschadel (cloverleaf skull) have been documented in historical literature.

Teratology

• Teratology is the science that studies the causes, mechanisms, and patterns of abnormal development.
• Congenital anomalies present at birth are classified into four types: malformation, disruption, deformation, and dysplasia.
• Malformation is a structural defect present at birth, which may be gross or microscopic, on the surface or within the body, and hereditary or non-hereditary.

Prevalence of Congenital Anomalies

• 3% of all live-born infants have a major congenital anomaly.
• Single minor anomalies are present in about 14% of newborns.
• Most severely malformed embryos are spontaneously aborted during the first 6-8 weeks of pregnancy.

Principles of Teratology

• Susceptibility to teratogenesis depends on the genotype of the conceptus and the interaction with adverse environmental factors.
• Susceptibility to teratogenesis varies with the developmental stage at the time of exposure.
• Teratogenic agents act in specific ways on developing cells and tissues to initiate sequences of abnormal developmental events.

Manifestations of Deviant Development

• There are four manifestations of deviant development: death, malformation, growth retardation, and functional defect.
• Manifestations of malformation increase in frequency and degree as dosage increases from the no observable adverse effect level to a dose producing 100% lethality.

Teratology Terms

• Malformation is a primary structural defect resulting from a localized error of morphogenesis.
• Disruption is a specific abnormality that results from disruption of normal developmental processes.
• Deformation is an alteration in shape or structure of a previously normally formed part.
• Syndrome is a recognized pattern of malformations with a given etiology.

Causes of Congenital Anomalies

• Genetic factors: chromosomal aberrations, numerical chromosomal abnormalities, structural chromosomal abnormalities, and mutant genes.
• Environmental factors: teratogens, including drugs, radiation, and other exogenous agents.