Teratology is the study of abnormalities of physiological development in organisms during their life span. It is a sub-discipline in medical genetics which focuses on the classification of congenital abnormalities in dysmorphology caused by teratogens. Teratogens are substances that may cause non-heritable birth defects via a toxic effect on an embryo or fetus. Defects include malformations, disruptions, deformations, and dysplasia that may cause stunted growth, delayed mental development, or other congenital disorders that lack structural malformations. The related term developmental toxicity includes all manifestations of abnormal development that are caused by environmental insult. The extent to which teratogens will impact an embryo is dependent on several factors, such as how long the embryo has been exposed, the stage of development the embryo was in when exposed, the genetic makeup of the embryo, and the transfer rate of the teratogen.
A birth defect is an abnormal condition that is present at birth, regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can range from mild to severe. Birth defects are divided into two main types: structural disorders in which problems are seen with the shape of a body part and functional disorders in which problems exist with how a body part works. Functional disorders include metabolic and degenerative disorders. Some birth defects include both structural and functional disorders.
Weissenbacher–Zweymuller syndrome (WZS), also called Pierre-Robin syndrome with fetal chondrodysplasia, is an autosomal recessive congenital disorder, linked to mutations in the COL11A2 gene, which codes for the α2 strand of collagen type XI. It is a collagenopathy, types II and XI disorder. The condition was first characterized in 1964 by G. Weissenbacher and Ernst Zweymüller.
A deformity, dysmorphism, or dysmorphic feature is a major abnormality of an organism that makes a part of the body appear or function differently than how it is supposed to.
Primrose syndrome is a rare, slowly progressive genetic disorder that can vary symptomatically between individual cases, but is generally characterised by ossification of the external ears, learning difficulties, and facial abnormalities. It was first described in 1982 in Scotland's Royal National Larbert Institution by Dr D.A.A. Primrose.
The VACTERL association refers to a recognized group of birth defects which tend to co-occur. This pattern is a recognized association, as opposed to a syndrome, because there is no known pathogenetic cause to explain the grouped incidence.
Caudal regression syndrome, or sacral agenesis, is a rare birth defect. It is a congenital disorder in which the fetal development of the lower spine—the caudal partition of the spine—is abnormal. It occurs at a rate of approximately one per 60,000 live births.
Simpson–Golabi–Behmel syndrome (SGBS) is a rare inherited congenital disorder that can cause craniofacial, skeletal, vascular, cardiac, and renal abnormalities. There is a high prevalence of cancer associated in those with SGBS which includes wilms tumors, neuroblastoma, tumors of the adrenal gland, liver, lungs and abdominal organs. The syndrome is inherited in an X-linked recessive manner. Females that possess one copy of the mutation are considered to be carriers of the syndrome but may still express varying degrees of the phenotype, suffering mild to severe malady. Males experience a higher likelihood of fetal death.
Monosomy 9p is a rare chromosomal disorder in which some DNA is missing or has been deleted on the short arm region, "p", of one copy of chromosome 9 (9p22.2-p23). This deletion either happens de novo or as a result of a parent having the chromosome abnormality. This rare chromosomal abnormality is often diagnosed after birth when developmental delay, irregular facial features, structural irregularities within the heart, and genital defects are observed. Treatments for this syndrome usually focus on fixing the malformations that are commonly associated with it. The cause of the syndrome was first discovered by Dr. Omar Alfi in 1973, when an analysis of the chromosomes of three infants with similar clinical abnormalities revealed that they all had a partial deletion of the short arm of Chromosome 9. Symptoms include micro genitalia, intellectual disability with microcephaly and dysmorphic features.
Holt–Oram syndrome is an autosomal dominant disorder that affects bones in the arms and hands and often causes heart problems. The syndrome may include an absent radial bone in the forearm, an atrial septal defect in the heart, or heart block. It affects approximately 1 in 100,000 people.
Duane-radial ray syndrome, also known as Okihiro syndrome, is a rare autosomal dominant disorder that primarily affects the eyes and causes abnormalities of bones in the arms and hands. This disorder is considered to be a SALL4-related disorder due to the SALL4 gene mutations leading to these abnormalities. It is diagnosed by clinical findings on a physical exam as well as genetic testing and imaging. After being diagnosed, there are other evaluations that one may go through in order to determine the extent of the disease. There are various treatments for the symptoms of this disorder.
Amelia is the birth defect of lacking one or more limbs. The term may be modified to indicate the number of legs or arms missing at birth, such as tetra-amelia for the absence of all four limbs. The term is from Ancient Greek ἀ- 'lack of' and μέλος 'limb'.
Dysmelia is a congenital disorder of a limb resulting from a disturbance in embryonic development.
Congenital amputation is birth without a limb or limbs, or without a part of a limb or limbs.
Renal dysplasia-limb defects syndrome, also known as Ulbright–Hodes syndrome, is a very rare autosomal recessive congenital disorder. It has been described in three infants, all of whom died shortly after birth.
Congenital hemidysplasia with ichthyosiform erythroderma and limb defects is a genetic disorder with onset at birth seen almost exclusively in females. The disorder is related to CPDX2, and also has skin and skeletal abnormalities, distinguished by a sharp midline demarcation of the ichthyosis with minimal linear or segmental contralateral involvement.
Roberts syndrome, or sometimes called pseudothalidomide syndrome, is an extremely rare autosomal recessive genetic disorder that is characterized by mild to severe prenatal retardation or disruption of cell division, leading to malformation of the bones in the skull, face, arms, and legs.
Constriction ring syndrome (CRS) is a congenital disorder with unknown cause. Because of the unknown cause there are many different, and sometimes incorrect, names. It is a malformation due to intrauterine bands or rings that produce deep grooves in extremities such as fingers and toes. In rare cases the constriction ring can form around other parts of the fetus and cause amputation or even intrauterine death. The anatomy proximal to the site of constriction is developmentally normal. CRS can be associated with other malformations, with club foot being most common. The precise configuration of the bands, lymphedema, and character of the amputations are not predictable and vary with each individual patient. Also, more than one extremity is usually affected, and it is rare for only one ring to present as an isolated malformation with no other manifestation of this syndrome.
XK aprosencephaly is an extremely rare congenital disorder characterized by the absence of the embryonic forebrain. Because the prosencephalon gives way to the cerebral cortex, survival with aprosencephaly is not possible outside utero. The external symptoms are similar to holoprosencephaly, a related disorder, including a smaller than normal head (microcephaly), small eyeballs (microphthalmia), a small mouth (microstomia), anal atresia, and abnormalities of the external genitalia, radius, nostrils, and pharynx (throat).
Hecht Scott syndrome is a rare genetic disease that causes congenital limb formation. The main characterisation is the aplasia or hypoplasia of bones of the limb. It is currently presenting in less than 1 in 1,000,000 newborns. It has been known to be more commonly present in males. It was first diagnosed in 2005 by Courtens et al. who recognised the malformations with his present case and four others that were similarly described in literature.
