Embryo Week 11 Limbs and Skin Defects

Defects!

T/F Minor birth defects of the limbs are relatively common and can be corrected surgically

True

T/F Birth defects of limbs are almost never part of a recognizable syndrome/pattern

False

When is the critical period of limb development?

24 -36 days after fertilization

What is the incidence of major defects of the limbs in neonates?

1:500

An Amelia limb defect arises at what stage of development?

Suppression of limb bud at 4th week

A meromelia limb defect arises at what stage of development?

Arrest/disturbance of differentiation/growth at 5th week

What 6 factors can cause limb defects?

Chromosomal abnormalities, single gene disorders, environmental factors, ischemia, mechanical influences, or multifactorial (most common)

What category of limb defect does thalidomide cause?

Most have amelia (absence of limbs), some had meromelia (Partial absence of limbs) 

Failure of development of the digital rays leads to what limb defect?

Ectrodactyly

What is the incidence and inheritance mode of ectrodactyly

1:20,000 live births, AD with incomplete penetrance

When does Ectrodactyly occur?

During 5th to 6th week of development

What causes cogenital absence of the radius 

Failure of mesenchymal primordium of radius to form during wk 5 of development

TAR syndrome stands for

Thrombocytopenia-absent radius

T/F Congenital absence of the radius is more often genetic than sporadic

False, it is more often sporadic

Name three syndromes that can include congenital absence of the radius

Holt-Oram, VACTERL, Fanconi Anemia

T/F Anomalies of the digits are all autosomal dominant traits

True

Brachydactyly definition

Short digits

Polydactyly definition

Supernumerary digits

Post axial polydactyly

On the outside of the hand (pinky side)

Pre axial polydactyly

On the inside of the hand (thumb side)

Syndactyly definition

Fused digits

The common name for Talipes equinovarus

Congenital clubfoot

Incidence of clubfoot

1:1000 births 

What is the most common musculoskeletal deformation

Congenital clubfoot

T/F Clubfoot is bilateral in 80% of cases

False, 50%

T/F Congenital clubfoot is 2x more common in males than females.

True

T/F Congenital clubfoot is associated with NTDs

True

What is the incidence of developmental hip dysplasia, is it more common in males or females

1:1500 neonates

What is the vernix formed from

Exfoliated peridermal cells

What is responsible for the formation of fingerprints

Epidermal ridges producing grooves

T/F 50% of down syndrome patients have distinct fingerprint patterns that can be used to help make a clinical diagnosis

True

Neural crest cells become the ____ of the developing ___

Neural crest cells become the mesenchyme of the developing dermis

Epidermis includes

Hair follicles, arrector muscles of hairs, sebaceous glands, sweat glands

Where does the dermis develop from?

Mesenchyme

When is the major vascular organization of the fetal dermis established?

End of 1st trimester

What is sebum?

Broken down central cells of hair follicles

Eccrine sweat glands shape

Coiled/tubular, function shortly after birth to control temp

Apocrine sweat glands function

Scent glands, armpits, groin, areolae, secretions don’t begin until puberty

When does mammary gland development begin?

Wk 4

Milk secretion is carried out via ? and ?

lactiferous ducts and alveoli

What period does hair develop in?

Fetal period

Name of the fine hair that covers the fetal skin

Lanugo

Do the hairs forming eyebrows and cilia of eyelashes have arrector muscles?

No

When do toenails and fingernails appear?

Week 10 gestation

Ectoderm forms what part of teeth?

Tooth enamel

When do the tooth buds appear

6th week of embryonic development

T/F Mandibular teeth usually erupt before maxillary

True

T/F boys teeth usually erupt sooner than girls

False

Most limb defects are a result of ? inheritance

Multifactorial

Ichthyosis definition

A general term for skin disorders resulting from excessive keratinization

Harlequin ichthyosis inheritance and symptoms

AR, thickened, ridged, and cracked skin. >50% of neonates die

Collodian infant symptoms

Covered by thick taut membrane that resembles parchment

Lamellar ichthyosis inheritance and symptoms

AR, persistant scaling, no sweat glands, less hair if any

Congenital Ectodermal Dysplasia definition

Rare, hereditary disorders involving tissues derived from the ectoderm

Lymphatic angioma

Cystic hygroma

True angioma

Benign tumors of endothelial cells

Nevus flammeus definition

Flat pink/red flame like blotch that often appears on posterior surface of the neck

T/F hemangioma is a larger, darker version of an angioma 

True

Sturge-Weber syndrome

A hemangioma in area of distribution of the trigeminal nerve which can be associated with a hemangioma of the brain seizures at birth

T/F It is rare that a hemangioma is a benign neoplasm

False

Albinism inheritance and gene

AR, TYR gene

Gynecomastia definition

Enlarged breast tissue in males due to development of rudimentary lactiferous ducts (more common in XXY males)

Chromosomal notation of Turner syndrome

45, X

Do people with turner syndrome have secondary sexual characteristics

No

Poland syndrome definition

Absent pectoral major muscle which can lead to hypoplasia/aplasia of breast tissue and nipple. 

Polymastia

Extra breast

Polythelia

Extra nipple

T/F Polythelia is isolated and not usually associated with other defects

False

Alopecia

Absence or loss of scalp hairs

? % of men and ?% of women have a scalp that is wholly or partially hairless at some point

70% of men and 40% of women have a scalp that is wholly or partially hairless at some point

Pili torti

Familial disorder where hairs are twisted and bent

Hypertrichosis

Excessive hairiness

Natal teeth inheritance and incidence

AD, 1:2000 neonates