Pachyonychia congenita

Author: Dr Sharnika Abeyakirthi, Dermatology Registrar, Waikato Hospital, Hamilton, New Zealand. Updated by Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. February 2014.

What is pachyonychia congenita?

Pachyonychia congenita is the name given to a group of rare, inherited disorders of keratinisation. Keratinisation is the process by which keratin (scale) is formed and deposited in the outer most layer of the skin. Pachyonychia congenita occurs when there is a mutation in the genes encoding keratin, K6a, K16, K17, K6b and, possibly, K6c (listed in decreasing frequency). Nearly 100 mutations have been described by the International Pachyonychia Congenita Research Registry (IPCRR, February 2014 [1]). The mutations cause the skin to be more fragile than usual.

Prior to genetic testing, some patients were diagnosed with pachyonychia congenita that actually did not have this disorder. Mutations in other keratin genes can lead to similar skin conditions.

How is pachyonychia congenita inherited?

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

No family history is present in many patients with pachyonychia congenita, due to sporadic mutations during conception.

Pachyonychia congenita is found in all ethnic groups and in equal numbers in males and females.

What are the features of pachyonychia congenita?

Pachyonychia congenita affects the skin (especially palms and soles), nails and mucous membranes. Specific features depend on which keratin gene is involved.

Pachyonychia congenita

Clinical features of pachyonychia congenita
Palms and soles	Thickened or calloused palms and soles (palmoplantar hyperkeratosis or keratoderma, particularly focal palmoplantar keratoderma), resulting in difficulty walking Focal palmoplantar keratoderma may be the only feature of pachyonychia congenital in patients with mutations of K6c. Pain is common and can be very severe, particularly in patients with mutations of K6a and K16 Hyperhidrosis (excessive sweating) Blisters precipitated by friction and warm weather
Nails	Nail changes are most severe with mutations of K6a and K16 Abnormalities of nails are apparent early in life Nails are thickened (pachyonychia), often with brownish discolouration All fingernails are commonly involved; toenails to a lesser degree. Specific K16 mutations do not affect fingernails
Cysts	Steatocystoma and pilosebaceous cysts are common, particularly in patients with mutations of K17 and to a lesser extent, K16a Cysts may or may not be painful
Dry skin	Friction sites such as knees and elbows may be dry due to scale around hair follicles (follicular hyperkeratosis) Tends to become less obvious in adult life
Mouth	White patches on tongue and inside cheeks (leukokeratosis) Sores at sides of mouth (angular cheilitis) Tooth abnormalities (natal or prenatal teeth)
Larynx	Hoarseness may occur

Classification of pachyonychia congenita

Pachyonychia congenita was traditionally classified into Type 1 and Type 2, according to the clinical features. Classification now depends on which keratin gene has the specific mutation.[2]

*IPCRR data summary as of December 2013
Clinical features	Percent affected with each genetic mutation
Clinical features	K6a	K6b	K6c	K16	K17
Thick toenails	99%	98%	56%	95%	99%
Thick fingernails	99%	51%	0	61%	87%
Plantar keratoderma	89%	98%	94%	100%	80%
Plantar pain	96%	100%	100%	97%	89%
Palmar keratoderma	54%	41%	19%	81%	51%
Cysts	68%	71%	25%	26%	92%
Follicular hyperkeratosis	62%	47%	0	14%	68%
Natal or prenatal teeth	2%	0	0	0	77%
Oral leukokeratosis	88%	31%	19%	41%	27%

*Data from 218, 49, 16, 150 and 90 patients with mutations of K6a, K6b, K6c, K16 and K17 respectively [2].

How is pachyonychia congenita diagnosed?

Pachyonychia congenita is usually diagnosed by its clinical appearance.

Skin biopsy 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. A genetic counsellor can advise whether the test is available in your area. Testing is available free of cost via Pachyonychia Congenita Project.

Prenatal testing is sometimes offered to pregnant women when they or a partner is affected by pachyonychia congenita. Pre-implantation diagnosis of ‘test-tube’ embryos has also been reported.

What is the treatment for pachyonychia congenita?

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

Treatment of keratoderma might include:

Emollients
Keratolytics, such as salicylic acid ointment, urea cream or other forms of heel balm
Mechanical debridement
Bleach baths to reduce infection
Pain relief
Oral retinoids, particularly acitretin.

Thickened nails should be regularly trimmed.

Experimental treatments are being offered to some patients with pachyonychia congenita as part of clinical trials of novel agents such as mTOR inhibitors (eg, sirolimus).

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