A father who says his son has no teeth

Correct answer: D. Hypohidrotic ectodermal dysplasia

• A. Cleidocranial dysplasia gives the opposite dental picture: retained primary teeth and multiple supernumeraries, along with hypoplastic or absent clavicles and open fontanelles.
• B. Ellis-van Creveld syndrome, which is chondroectodermal dysplasia, features polydactyly, short-limbed dwarfism, natal teeth and a fused upper labial frenum.
• C. Papillon-Lefevre syndrome causes palmoplantar hyperkeratosis with aggressive periodontitis and premature loss of teeth that did erupt, not failure of teeth to form.
• D. Correct. The triad of hypodontia or anodontia, hypotrichosis and hypohidrosis, presenting with dry skin, periorbital wrinkling, frontal bossing and a saddle nose, defines hypohidrotic ectodermal dysplasia, also called Christ-Siemens-Touraine syndrome. All the affected structures are ectodermal derivatives.

Correct answer: C. Refer for coordinated multidisciplinary care including paediatrics and genetics

• A. Implants are contraindicated in a growing child. Placed before jaw growth completes, they behave like ankylosed teeth and end up in infraocclusion as the alveolus develops around them.
• B. Passive observation misses the thermoregulatory risk and delays the speech, nutrition and psychosocial benefits of early prosthetic care. Overdentures can be provided from around age three.
• C. Correct. The dental findings are one part of a systemic condition. The most urgent issue is thermoregulation, since a child who cannot sweat is at genuine risk of hyperthermia. Paediatrics, genetics, dermatology and dentistry need to coordinate, and prosthetic rehabilitation is staged within that framework.
• D. The conical teeth are valuable. They are retained as overdenture abutments to preserve alveolar bone and improve retention and proprioception.

Note: Removable overdentures are the usual first prosthesis, remade periodically as the child grows. Implants wait until growth is complete, roughly 17 to 18 years in males.

Correct answer: B. Dry eyes from deficient lacrimal secretion

• A. Bifid ribs are a feature of Gorlin-Goltz syndrome, alongside multiple odontogenic keratocysts and basal cell carcinomas.
• B. Correct. Lacrimal glands are ectodermal derivatives, so they are hypoplastic in this condition. Reduced tear production causes dry eyes and photophobia. Nail dystrophy, absent or hypoplastic salivary and mucous glands, and a hoarse voice from dry respiratory mucosa follow the same logic.
• C. Palmoplantar hyperkeratosis belongs to Papillon-Lefevre syndrome. This distractor has appeared as a miskeyed answer in earlier files in the series, so it is worth fixing in memory.
• D. The adrenal cortex arises from intermediate mesoderm, not ectoderm, so adrenal function is unaffected. This is the reasoning behind the 'all except' version of this question.

Correct answer: C. It follows a Y-linked pattern of inheritance

• A. This is true. Skin glands and hair follicles are ectodermal, so the skin is dry and the hair sparse, fine and light in colour.
• B. This is true. Periorbital wrinkling with hyperpigmentation, frontal bossing, a depressed nasal bridge and everted lips give the recognisable facies.
• C. Correct, and this is the exception. The classic form is X-linked recessive, caused by mutations in the EDA gene at Xq12-13. It is not Y-linked. A Y-linked condition would pass only father to son and would never appear in females, which is not the pattern seen.
• D. This is true and follows from X-linked recessive inheritance. Males, being hemizygous, are fully affected, while carrier females show milder patchy signs such as a few missing or conical teeth and reduced sweating in a mosaic distribution.

Note: An autosomal recessive form also exists and affects both sexes equally, but the X-linked form is the one tested.

Correct answer: B. Oral mucosal epithelium

• A. Cementum arises from the dental follicle, another ectomesenchymal derivative, as do the periodontal ligament and alveolar bone proper.
• B. Correct, and this is the exception. Oral mucosal epithelium arises from surface ectoderm directly, not from ectomesenchyme. Enamel likewise comes from ectodermally derived ameloblasts of the enamel organ.
• C. Dentin is produced by odontoblasts, which differentiate from the dental papilla, an ectomesenchymal tissue derived from migrating neural crest cells.
• D. The dental pulp is the mature dental papilla and is therefore ectomesenchymal.