Important Concepts and Definitions Flashcards
Define dysmorphology
The study of genetic syndromes and congenital birth defects that alter the shape or form of one or more parts of the body of a newborn child.
What is the importance of making an accurate genetic diagnosis?
A confirmed diagnosis may provide closure.
This will allow the geneticist to have clear discussions with the family about:
- Prognosis,
- Natural history,
- Recommended surveillance and monitoring,
- Additional investigations that may be required,
- Referrals to specialists who may need to be involved
And provide accurate counseling around:
- Mode of inheritance,
- Recurrence risk,
- Health implications on other family members,
- Prenatal screening and diagnostic options.
The family can be given details of support groups and are empowered to access further information.
Define malformation with example(s).
Primary error of morphogenesis; NON-PROGRESSIVE, congenital MORPHOLOGICAL ANOMALY of a single organ or body part that results from intrinsic abnormalities in one or more genetic programs OPERATING in development.
Eg. cleft lip, cleft palate, polydactyly.
MNEMONIC: When something isn’t formed properly.
Define deformation with example(s).
DEFECTS which are caused by EXTRINSIC factors which cause an ABERRANT mechanical force that DISTORTS the otherwise normal structure.
Eg. flat nasal bridge (oligohydramnios); arthrogryposis (twin pregnancy or oligohydramnios).
NB: Most resolve spontaneously or can be treated by external fixation devices to reverse the effects of the instigating cause.
Define disruption with example(s).
NON-PROGRESSIVE, congenital MORPHOLOGICAL ANOMALY of a body part that results from destruction of irreplaceable NORMAL fetal tissue which had NORMAL developmental potential.
Eg. vascular insufficiency, trauma, teratogens, amniotic disruption/bands.
Define dysplasia with example(s).
MORPHOLOGICAL ANOMALY arising either prenatally or postnatally from DYNAMIC or ongoing alteration of cellular constitution, tissue organization, or function within a specific organ or a specific tissue type.
E.g. within cartilage and bone in skeletal dysplasias.
Define syndrome with example(s).
A characteristic PATTERN of ANOMALIES, ONE of which is morphologic, presumed to be causally related.
E.g. Marfan syndrome
Define sequence with example(s).
One or more SECONDARY morphologic anomalies, known or presumed to CASCADE from a SINGLE primary malformation, disruption, dysplasia, or deformation.
E.g. Pierre Robin sequence
Define association with example(s).
A PATTERN of ANOMALIES, at least TWO of which are morphologic, that occur together more often than would be expected by chance and where a causal relationship has not been identified.
E.g. VACTERL
— % of singleton neonates have an obvious major congenital anomaly?
— % of MZ twins are born with a congenital anomaly?
— % of children with a difficult-to-diagnose developmental disorder will have a composite phenotype caused by the co-occurrence of two distinct genetic disorders.
2-3%
~ 10%
~ 5%
Why is it important to determine the mechanism by which a birth defect has arisen?
This has important implications on prognosis, recurrence risk, and decision making around genetic testing as only malformations and dysplasias are genetic.
