Developmental Genetics Terminology

Question 1

What are malformations?

Answer 1

Malformation: this is an abnormality that arises because of a primary error in morphogenesis – due to an abnormal developmental process

• In other words: due to errors occurring in the initial formation of structures; a primary structural defect of an organ or part of an organ.

• Examples include:
‒ Congenital heart abnormalities
‒ Cleft lip / cleft palate ‒ Polydactyly.
• Many are multifactorial.

Question 2

What is a malformation sequence?

Answer 2

• Sometimes called “Malformation sequence:”
• A cascade of effect resulting from a single primary malformation ‒ Creates a recognizable pattern of multiple defects

• An example is the Pierre Robin sequence of head and facial abnormalities
‒ Micrognathia (formation of a small lower jaw) is the initial event
‒ Causes the tongue to form further back than normal (glossoptosis)
‒ Leads to obstruction of the airways; feeding difficulties
‒ High risk for cleft palate

Question 3

What is malformation syndrome?

Answer 3

A pattern of features that are known to have a unifying underlying cause.

‒Manifestations arise from several different points during morphogenesis
‒Syndrome is from the Greek: running together

• Example: Down syndrome (trisomy 21) ‒Not all features need to be present to
make the diagnosis
‒People with some of the features might not have the disorder

Question 4

What are disruptions?

Answer 4

Disruptions are due to destruction of a tissue or organ after it has been formed.

• Results in an abnormal structure of a tissue or organ or as a result of external forces

• Usually this is not a genetically controlled event ‒ Example: amniotic band disruption
‒ Caused by fibrous amniotic bands while in utero
‒ Each is different - may result in finger amputation, or fusion of digits

Question 5

What are deformations?

Answer 5

Deformations might be thought of as mechanical distortions by a physical force upon an otherwise normal structure

• This is occurring while the tissue is forming
‒ e.g.clubfoot that is caused by lack of amniotic fluid or intra-uterine crowding. ‒

Deformations might be surgically correctable, or they might resolve after
birth.

Question 6

What are dysplasias?

Answer 6

Dysplasia is an abnormality in a tissue structure caused by abnormal cellular organization.

• Example, disorders caused by FGFR3 mutation such as achondroplasia which affects many aspects of skeletal structure.

Question 7

What are associations?

Answer 7

Associations are where traits coincide more often than expected by chance.

‒ Traits are seemingly unconnected
‒ A single genetic cause is not known.

• Only a subset of conditions are needed to fit
• Some affected patients might have additional defects