Characteristic skin lesion in Peutz-Jeghers syndrome is
**Core Concept**
Peutz-Jeghers syndrome is a genetic disorder characterized by the development of benign hamartomatous polyps in the gastrointestinal tract, accompanied by distinctive mucocutaneous melanin deposits. These skin lesions are a hallmark of the disease, resulting from an abnormal increase in melanin production.
**Why the Correct Answer is Right**
The characteristic skin lesion in Peutz-Jeghers syndrome is a bluish or dark brown macule, often located on the lips, oral mucosa, hands, and feet. These lesions are caused by an accumulation of melanin in the basal layer of the epidermis, due to the increased activity of the enzyme tyrosinase, which is responsible for converting the amino acid tyrosine into melanin. The melanin then accumulates in the keratinocytes, leading to the formation of the characteristic skin lesions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the characteristic skin lesion in Peutz-Jeghers syndrome. While melanocytic nevi are common skin lesions, they are not associated with Peutz-Jeghers syndrome.
**Option B:** This option is incorrect because the skin lesions in Peutz-Jeghers syndrome are not caused by an abnormal increase in keratin production. Instead, they result from an abnormal increase in melanin production.
**Option C:** This option is not a characteristic skin lesion in Peutz-Jeghers syndrome. While dermatofibromas are common skin lesions, they are not associated with Peutz-Jeghers syndrome.
**Clinical Pearl / High-Yield Fact**
The skin lesions in Peutz-Jeghers syndrome are often referred to as "labial melanotic macules." These lesions can appear as early as infancy and are often a key diagnostic feature of the disease.
**Correct Answer: A. Melanotic macules.**