Pachyonychia congenita

What is pachyonychia congenita?

Pachyonychia congenita is a rare, inherited disorder of keratinisation. This is the process by which keratin is formed and deposited in the outer most layer of the skin. It occurs due to mutation in the genes encoding keratin 6a, 6b, 16 and 17.

How is it inherited?

Pachyonychia congenita is most often autosomal dominantly inherited. That means the defective gene comes from one parent. An affected person has a 50% chance of passing on the disease to his or her offspring at each pregnancy.

A few cases of autosomal recessive pachyonychia congenita have also been reported, in which a family history may not be known as the abnormal gene is inherited from both parents. In this case, on average, one in every four of the offspring are affected.

Sporadic cases may also arise, due to mutations during conception.

What are the features of pachyonychia congenita?

Pachyonychia congenita affects the skin (especially palms and soles), nails, hair and mucous membranes.

Pachyonychia congenita

Clinical feature of pachyonychia congenita
Palms and soles	Painful thickened palms and soles (palmoplantar hyperkeratosis or keratoderma), resulting in difficulty walking Hyperhidrosis (excessive sweating) Blisters precipitated by friction and warm weather
Nails	Abnormal nails apparent early in life Nails are thickened with brownish discolouration All finger nails are commonly involved; toe nails to a lesser degree
Hair	Coarse unruly hair Sometimes loss of hair (alopecia)
Eyes	Corneal opacities Cataracts
Larynx	Hoarseness may occur Rarely, respiratory obstruction and death in infancy

Classification of pachyonychia congenita

Pachyonychia congenita is classified into at least two types according to the clinical features,. Particular features may be more prominent in some patients than in others.

Pachyonychia congenita type 1

Type 1 (MIM# 167200) is also known as the Jadassohn-Lewandowsky type of pachyonychia congenita. Features are:

• Nail changes
• Palmoplantar hyperkeratosis
• Follicular hyperkeratosis (thickened horny plugs) on the face & extensor surfaces of the limbs
• Oral leukokeratosis (whitish areas inside the mouth)

Pachyonychia congenita type 2

Type 2 (MIM# 167201) or the Jackson-Lawler type of pachyonychia congenita includes the features of type 1 plus:

• Natal (birth) teeth
• Steatocystoma multiplex
• Epidermoid cysts
• Hair abnormalities

How is Pachyonychia congenita diagnosed?

Pachyonychia congenita is diagnosed by its clinical appearance.

Skin biopsies of the affected tissues will only show nonspecific changes.

Molecular genetic studies can be done by specialist laboratories to detect mutations in the affected keratin genes.

Treatment

Unfortunately there is no cure for pachyonychia congenita. The effectiveness of treatment depends on the severity of the specific problem.

Treatment might include:

• Emollients
• Keratolytics e.g. salicylic acid ointment
• Mechanical debridement
• Oral retinoids e.g. acitretin