Developmental disorders

Question 1

What happens during fertilisation?

Answer 1

• 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

Question 2

What happens at day 2-3 of development?

Answer 2

• 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

Question 3

What happens at say 4-5 of development?

Answer 3

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

Question 4

What happens at day 6-7 of development?

Answer 4

• A bilaminar disc forms as the embryo implants

- The inner cell mass differentiates into the epiblast and hypoblast

Question 5

What forms from the hypoblast?

Answer 5

The extraembryonic membranes

Question 6

What forms from the epiblast?

Answer 6

The embryo and amniotic cavity

Question 7

What happens at day 6-8 of development?

Answer 7

The exocoelomic membrane forms from the hypoblast and creates the yolk sac which contains nutrients that supply the embryo before the placenta functions

Question 8

What happens at 3 weeks+ of development?

Answer 8

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

Question 9

What happens at week 4+ of development?

Answer 9

The flat disc folds in 2 directions

Question 10

What do dermomyotomes form?

Answer 10

Connective tissue and skeletal muscle

Question 11

What do Sclerotomes form?

Answer 11

Bone and cartilage

Question 12

How do dermomyotomes and sclerotomes form?

Answer 12

Somites are paired blocks of tissue that differentiate from the paraxial mesoderm. The somites will undergo further differentiation to form dermomyotomes and sclerotomes

Question 13

What is a LTRA?

Answer 13

A leukotriene receptor antagonist

Question 14

What are the effects of a filaggrin gene defect?

Answer 14

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

Question 15

What are single birth defects?

Answer 15

The most common group of defects with multifactorial causation and a low recurrence risk
Eg. Cleft palate, cardiac defects, and congenital hip dysplasia

Question 16

What is the difference between a syndrome and an association?

Answer 16

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

Question 17

What is a sequence in developmet?

Answer 17

Multiple anomalies related to a single primary anomaly or mechanical factor
Eg. Amniotic band syndrome, Potter’s syndrome

Question 18

What is amniotic band sequence?

Answer 18

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

Question 19

What is Potter’s sequence?

Answer 19

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

Question 20

What is the definition of a teratogen?

Answer 20

Environmental agents with potential to induce a structural anomaly in the developing foetus

Question 21

What are the consequences of a congenital infection (TORCH)?

Answer 21

Growth restriction
Cataracts
Hearing impairment
Microcephaly
Learning difficulties

Rubella used to be the most common cause before vaccines. Now it’s CMV

Question 22

What is foetal alcohol syndrome?

Answer 22

Caused when the mother drinks alcohol during pregnancy

Causes a smooth filtrum, thin upper lip, short palpebral fissures, growth restriction, learning difficulties

Question 23

Which conditions are more common if the mother has diabetes?

Answer 23

Cardiac and neural tube defects

Question 24

What is imprinting in genetics?

Answer 24

The ability of a gene to be expressed depends upon the sex of the parent who passed on the gene

Question 25

What are some dysmorphic features of down syndrome?

Answer 25

Flat nasal bridge, epicanthic folds, protruding tongue, clinodactyly, single palmar crease, sandal-toe gap

Question 26

What are some clinical feature of Turner syndrome?

Answer 26

Short stature
Wide carrying angle
Neck webbing
Widely-spaced nipple
Streak ovaries/ ovarian failure
Learning difficulties
Cardiac anomalies

Question 27

What is neurofibromatosis type 1?

Answer 27

Causes tumours to grow along nerves

Clinical features: Cafe-au-lait spots, neurofibromas, freckling, Lisch nodules, optic gliomas, learning difficulties, pheochromocytomas

Question 28

What is Duchenne’s muscular dystrophy?

Answer 28

Most common X-linked disorder affecting the DMD gene coding for dystrophin

Causes delayed motor milestones, progressive proximal muscle weakness, hypertrophy of calf muscles

Question 29

What is fragile X syndrome?

Answer 29

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

Question 30

What is Prader-Willi/Angleman’s syndrome?

Answer 30

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