Developmental disorders Flashcards
What happens during fertilisation?
- The sperm meets the ovum usually in the ampulla 12-24 hours after ovulation
- The sperm penetrates the corona radiate and zona pellucida and they fuse
- The acrosome reaction makes the ovum impermeable to other sperm
What happens at day 2-3 of development?
- Cleavage occurs
- First mitotic division is about 30 hours after fertilisation
By day 3, there is a 16 cell embryo. Each cells is called a blastomere and the solid sphere is known as a morula
What happens at say 4-5 of development?
The morula develops a cavity and becomes known as a blastocyst. The outer layer of cells of the blastocyst becomes the trophoblast
The blastocyst reaches the uterine lumen and becomes ready for implantation
What happens at day 6-7 of development?
- A bilaminar disc forms as the embryo implants
- The inner cell mass differentiates into the epiblast and hypoblast
What forms from the hypoblast?
The extraembryonic membranes
What forms from the epiblast?
The embryo and amniotic cavity
What happens at day 6-8 of development?
The exocoelomic membrane forms from the hypoblast and creates the yolk sac which contains nutrients that supply the embryo before the placenta functions
What happens at 3 weeks+ of development?
Gastrulation
- The epiblast becomes the ectoderm, hypoblast becomes the endoderm, and the mesoderm forms
The hypoblast degenerates and the epiblast gives rise to all the 3 layers
What happens at week 4+ of development?
The flat disc folds in 2 directions
What do dermomyotomes form?
Connective tissue and skeletal muscle
What do Sclerotomes form?
Bone and cartilage
How do dermomyotomes and sclerotomes form?
Somites are paired blocks of tissue that differentiate from the paraxial mesoderm. The somites will undergo further differentiation to form dermomyotomes and sclerotomes
What is a LTRA?
A leukotriene receptor antagonist
What are the effects of a filaggrin gene defect?
About 15% of children in the UK have it.
It causes eczema, allergic rhinitis, and food allergies because the defect causes hypersensitivity of the skin barrier
What are single birth defects?
The most common group of defects with multifactorial causation and a low recurrence risk
Eg. Cleft palate, cardiac defects, and congenital hip dysplasia
What is the difference between a syndrome and an association?
Syndrome: present in a consistent pattern with common cause and recurrence rate Eg. Chromosomal abnormalities
Association: Two or more congenital anomalies occur together more often than expected but with no well-defined aetiology
What is a sequence in developmet?
Multiple anomalies related to a single primary anomaly or mechanical factor
Eg. Amniotic band syndrome, Potter’s syndrome
What is amniotic band sequence?
When the inner layer (amnion) of the amniotic sac ruptures or tears, exposing the foetus to strands of fibrous tissue that may float freely in the amniotic fluid or remain partially attached to the amniotic sac
If it wraps around limbs, is can cause growth restriction or malformations
What is Potter’s sequence?
It describes the typical physical appearance caused by pressure in utero due to oligohydramnios
It can occur in conditions such as infantile polycystic kidney disease, renal hypoplasia, and obstructive uropathy
What is the definition of a teratogen?
Environmental agents with potential to induce a structural anomaly in the developing foetus
What are the consequences of a congenital infection (TORCH)?
Growth restriction Cataracts Hearing impairment Microcephaly Learning difficulties
Rubella used to be the most common cause before vaccines. Now it’s CMV
What is foetal alcohol syndrome?
Caused when the mother drinks alcohol during pregnancy
Causes a smooth filtrum, thin upper lip, short palpebral fissures, growth restriction, learning difficulties
Which conditions are more common if the mother has diabetes?
Cardiac and neural tube defects
What is imprinting in genetics?
The ability of a gene to be expressed depends upon the sex of the parent who passed on the gene
What are some dysmorphic features of down syndrome?
Flat nasal bridge, epicanthic folds, protruding tongue, clinodactyly, single palmar crease, sandal-toe gap
What are some clinical feature of Turner syndrome?
Short stature Wide carrying angle Neck webbing Widely-spaced nipple Streak ovaries/ ovarian failure Learning difficulties Cardiac anomalies
What is neurofibromatosis type 1?
Causes tumours to grow along nerves
Clinical features: Cafe-au-lait spots, neurofibromas, freckling, Lisch nodules, optic gliomas, learning difficulties, pheochromocytomas
What is Duchenne’s muscular dystrophy?
Most common X-linked disorder affecting the DMD gene coding for dystrophin
Causes delayed motor milestones, progressive proximal muscle weakness, hypertrophy of calf muscles
What is fragile X syndrome?
Affects mostly Males and is caused by a trinucleotide repeat disorder
It causes a broad forehead, elongated face, large prominent ears, pectus excavatum, mitral valve prolapse, hypotonia, flat feet, seizures
What is Prader-Willi/Angleman’s syndrome?
Caused by de novo deletions on chromosome 15 and in a phenomenon of imprinting
PWS: caused when there is a deletion of paternally inherited copy. It causes problems with eating habits
Angleman’s: deletion of the maternally inherited copy. Causes learning difficulties
