Page 272 - Textbook of Pathology, 6th Edition

256
Genetic and
Chapter 10
Chapter 10
Paediatric Diseases

This chapter deals with the group of disorders affecting the Classification
SECTION I
foetus during intrauterine life (genetic as well as Various developmental anomalies resulting from teratogenic
developmental) and paediatric age group. In the western effects are categorised as under:
countries, developmental and genetic birth defects constitute
about 50% of total mortality in infancy and childhood, while Agenesis means the complete absence of an organ e.g.
in the developing and underdeveloped countries 95% of unilateral or bilateral agenesis of kidney.
infant mortality is attributed to environmental factors such Aplasia is the absence of development of an organ with
as poor sanitation and undernutrition. presence of rudiment or anlage e.g. aplasia of lung with
For the purpose of convenience of discussion, genetic and rudimentary bronchus.
paediatric diseases are covered under the following headings: Hypoplasia is incomplete development of an organ not
1 Developmental defects: Errors in morphogenesis reaching the normal adult size e.g. microglossia.
2. Cytogenetic (Karyotypic) defects: chromosomal abnor- Atresia refers to incomplete formation of lumen in hollow
malities viscus e.g. oesophageal atresia.
3. Single-gene defects: Mendelian disorders
4. Multifactorial inheritance disorders Developmental dysplasia is defective development of cells
5. Other paediatric diseases and tissues resulting in abnormal or primitive histogenetic
Though many of diseases included in the groups above structures e.g. renal dysplasia (Developmental dysplasia is quite
have been discussed along with relevant chapters later, broad different from cellular dysplasia in relation to precancerous
overview of these disorders is presented below. lesions discussed earlier on page 58).
Dystraphic anomalies are the defects resulting from failure
of fusion e.g. spina bifida.
DEVELOPMENTAL DEFECTS
Ectopia or heterotopia refers to abnormal location of tissue
General Pathology and Basic Techniques
at ectopic site e.g. pancreatic heterotopia in the wall of
Developmental defects are a group of abnormalities during
foetal life due to errors in morphogenesis. The branch of stomach.
science dealing with the study of developmental anomalies
is called teratology. Certain chemicals, drugs, physical and Examples of Developmental Defects
biologic agents are known to induce such birth defects and A few common clinically important examples are given
are called teratogens. The morphologic abnormality or defect below:
in an organ or anatomic region of the body so produced is 1. Anencephaly-spina bifida complex. This is the group of
called malformation. anomalies resulting from failure to fuse (dystraphy). While
anencephaly results from failure of neural tube closure, spina
Pathogenesis
bifida occurs from incomplete closure of the spinal cord and
The teratogens may result in one of the following outcomes: vertebral column, often in the lumbar region. The latter
i) Intrauterine death results in meningocele or meningomyelocele.
ii) Intrauterine growth retardation (IUGR) 2. Thalidomide malformations. Thalidomide is the best
iii) Functional defects known example of teratogenic drug which was used as a
iv) Malformation sedative by pregnant women in 1960s in England and
The effects of teratogens in inducing developmental
defects are related to the following factors: Germany and resulted in high incidence of limb-reduction
anomalies (phocomelia) in the newborns.
Variable individual susceptibility to teratogen: All patients
exposed to the same teratogen do not develop birth defect. 3. Foetal hydantoin syndrome. Babies born to mothers on
Intrauterine stage at which patient is exposed to teratogen: anti-epileptic treatment with hydantoin have characteristic
Most teratogens induce birth defects during the first trimester facial features and congenital heart defects.
of pregnancy. 4. Foetal alcohol syndrome. Ethanol is another potent
Dose of teratogen: Higher the exposure dose of teratogen, teratogen. Consumption of alcohol by pregnant mother in
greater the chances of inducing birth defects. first trimester increases the risk of miscarriages, stillbirths,
Specificity of developmental defect for specific teratogen: A growth retardation and mental retardation in the newborn.
particular teratogen acts in a particular way and induces the 5. TORCH complex. Infection with TORCH group of
same specific developmental defect. organisms (Toxoplasma, Others, Rubella, Cytomegalovirus,