Dysmorphology/ Terminology

Question 1

Malformation

Answer 1

● Structural difference arising from a primary localized error in morphogenesis
● Due to inherent abnormal development
● Examples:
o Congenital heart defect
o Polydactyly
o Cleft palate in Van der Woude syndrome/as a result of a genetic mutation

Question 2

VACTERL

Answer 2

● Vertebral anomalies
● Anal atresia
● Cardiac defects
● Tracheoesophageal fistula
● Esophageal atresia
● Renal and radial anomalies
● Limb defects

Question 3

Sequence

Answer 3

A pattern of multiple defects resulting from a single primary malformation

Question 4

Pierre-Robin Sequence

Answer 4

Micrognathia leads to cleft palate and glossoptosis (tongue placed further back in the
mouth/throat than usual) and subsequent respiratory distress

Question 5

Potter Sequence

Answer 5

Distinct physical appearance caused by oligohydramnios (not enough amniotic fluid),
which itself is often secondary to renal agenesis or other renal malformations

Question 6

Deformation

Answer 6

An alteration in the shape or structure of a body part, that is otherwise differentiating
normally, as the result of non-disruptive mechanical forces
● Examples:
o Potter sequence (oligohydramnios)
o Pierre-Robin sequence (cleft-lip and palate due to micrognathia)

Question 7

Disruption

Answer 7

Structural defect resulting from destruction of a body part that has already
differentiated normally
● Example:
o Amniotic bands

Question 8

Arthrogryposis

Answer 8

Congenital joint contracture in two or more areas of the body

Question 9

Amyoplasia

Answer 9

● Literally “no muscle growth”
● Form of arthrogryposis
● Internally rotated shoulders, ulna deviation, extended elbows and knees, equinovarus
contractures
● Replacement of skeletal muscle by dense fibrous tissue and fat
● May also include vascular compromise
● Occurs sporadically due to lack of fetal movement which may be due to an
external/environmental factor (oligohydramnios/bicornuate uterus)

Question 10

Klippel-Feil Anomaly

Answer 10

● Congenital fusion of any two of the seven cervical vertebrae
● May be caused by mutations in GDF3 and GDF6
● Autosomal dominant form at 8q22.2 also associated with laryngeal malformation

Question 11

Locus Heterogeneity

Answer 11

Mutations in different genes can cause the same disorder/phenotypic presentation
o Ex. Autism, retinitis pigmentosa

Question 12

Allelic Heterogeneity

Answer 12

Different mutations/alleles on the same gene can cause the same disorder
o Ex. Cystic fibrosis

Question 13

Phenotypic Heterogeneity

Answer 13

Different mutations in the same gene can cause different phenotypes
o Ex. RET, FGFR3

Question 14

Pleiotropy

Answer 14

● One gene mutation influences many unrelated phenotypic traits
o Ex. PKU, Sickle-cell, affect multiple body systems

Question 15

Variable Expressivity

Answer 15

● One condition can have many different phenotypic presentations/exist on a spectrum
● Individuals with the condition may present with some or all of these features and it can
vary between relatives with the same mutation
● Ex. NF1

Question 16

Penetrance

Answer 16

How likely a mutation in a gene is to lead to disease
● Reduced penetrance results in mutation carriers who may not ever present with disease