Expanding our concepts of mosaic disorders of skin

Two new patients with focal dermal hypoplasia: A novel PORCN variant and insights on the diagnostic considerations

Mutations in the PORCN gene cause an X-linked dominant condition; focal dermal hypoplasia (FDH), characterized by atrophic skin, pigmented skin lesions in addition to several ocular and skeletal malformations. FDH is rare with around 275 cases reported so far from diverse ethnic groups. Herein, we provide a report of two new patients with FDH from Egypt. In addition to the typical clinical manifestations of the disease, infrequently reported clinical findings in the form of broad metaphysis, bilateral short broad femurs, and dermal sinus over the sacrum were seen in Patient 1 and partial fusion of labia majora, ventral hernia, and bladder extrophy were present in Patient 2. Two heterozygous protein-truncating PORCN mutations were identified in our patients, a known nonsense c.370C>T p.(Arg124Ter) and a novel frameshift c.375delG p.(Ala126HisfsTer3). Segregation analyses confirmed that the two mutations were "de novo" and not inherited from any of the parents. Our study expands the clinical and mutational spectrum of focal dermal hypoplasia and emphasizes the importance of investigating the different body systems and organs for the early management of patients.

Inherited ichthyoses/generalized Mendelian disorders of cornification

Inherited ichthyoses, defined as the generalized form of Mendelian disorders of cornification, are characterized by visible scaling and/or hyperkeratosis of most or all of the skin. This etiologically and phenotypically heterogenous group of conditions is caused by mutations in various different genes important for keratinocyte differentiation and epidermal barrier function. Diagnosing a specific entity is a particular challenge for the nonspecialist presented with the common clinical scaling. For the clinician, this review outlines an algorithmic approach for utilizing diagnostic clues to narrow down the differential diagnosis and to guide further testing and treatment options.

Syndromic nevoid hypermelanosis: description of seven cases with a 10-year follow up

Skin lesions can often be the only sign of an underlying systemic abnormality which will require further investigation. Several syndromic conditions are diagnosed after their cutaneous marker, which is in most cases a nevus. We report a neurocutaneous condition which we named "syndromic nevoid hypermelanosis" (SNH). We studied seven patients who presented with hyperpigmented disseminated macules (melanotic or pigmented nevi) as a cardinal sign. Neurological abnormalities were detected in all cases and skeletal dysmorphism in four. In spite of the genetic alteration that may be the cause of this disease, dermatologists should be able to diagnose it based on its semiological features and distinguish it from other neurocutaneous conditions. We consider SNH to be a distinct clinical entity that has not been clearly defined until now.

A case of hypermelanosis in a phylloid pattern

Pigmentary anomalies display a variety of different patterns. The phylloid pattern is characterized by a leaf-shaped arrangement reminiscent of floral ornaments. We describe a 20-year-old Korean man with hyperpigmented oblong patches and atypically short, thick hairs in a phylloid pattern on the face, the left shoulder, and the left side of the trunk. Associated musculoskeletal anomalies included equinovarus deformities, bilateral club foot, lumbar lordosis, spina bifida, and relative hypertrophy of the right thigh muscles.

Squamous cell carcinoma in a linear epidermal nevus

An 81-year-old African American female presented with a 3-year history of a slow, persistently enlarging mass on the medial aspect of her left thigh. Her past history was remarkable for a congenital linear epidermal naevus that was present on the inner aspect of her left thigh. A biopsy of the mass was performed and histology results confirmed the diagnosis of a well differentiated squamous cell carcinoma. Such an occurrence is extremely rare and less than 10 cases have been reported in the literature.

Two squamous cell carcinomas arising in a linear epidermal naevus in a 28-year-old female

The development of a squamous cell carcinoma (SCC) in a linear epidermal naevus is a rare event previously reported in long-standing and often extensive lesions of middle-aged to elderly patients. To the best of our knowledge, this case appears to be only the second report of an SCC arising in a linear epidermal naevus in a young patient and the first report of two SCCs developing in a small epidermal naevus, over a short time, in a young patient with no other risk factors.

Congenital curvilinear palpable hyperpigmentation

We report two cases of congenital curvilinear palpable hyperpigmentation on the posterior aspect of bilateral legs in male infants. These lesions appeared shortly after birth and mimicked child abuse with looped cord or postinflammatory hyperpigmentation. Histopathologic features showed lentiginous melanocytic hyperplasia. One of the boys also had severe global developmental delay with abnormal findings from magnetic resonance imaging of the brain. We believe that these lesions represent a new type of congenital hyperpigmentation that we termed "congenital curvilinear palpable hyperpigmentation." Although these lesions do not follow the lines of Blaschko, they may also be associated with neurologic and developmental abnormalities.

Linear nevus comedonicus with epidermolytic hyperkeratosis

BACKGROUND

Nevus comedonicus (NC) is rarely associated with the histopathologic pattern of follicular epidermolytic hyperkeratosis (EHK). We found eight cases reported. In one case, the condition was transmitted to the offspring in the form of generalized EHK.

METHODS

We describe a case of linear NC with EHK in a 46-year-old woman.

RESULTS

Histopathologic examination revealed the typical features of NC. Additionally, the follicular epithelial walls showed EHK with characteristic perinuclear vacuolization in the stratum spinosum and stratum granulosum and large, irregular keratohyalin granules in the granular cell layer.

CONCLUSIONS

The clinical and histopathologic features of this case are consistent with a diagnosis of linear NC with EHK. Lesions of NC suspected by clinical exam should be examined microscopically to look for features of EHK. If present, patients should be educated about the risk, albeit rare, of passing on a more severe form of the disorder to subsequent generations.

Costs and benefits of genetic heterogeneity within organisms

An increasing number of studies have recently detected within-organism genetic heterogeneity suggesting that genetically homogeneous organisms may be rare. In this review, we examine the potential costs and benefits of such intraorganismal genetic heterogeneity (IGH) on the fitness of the individual. The costs of IGH include cancerous growth, parasitism, competitive interactions and developmental instability, all of which threaten the integrity of the individual while the potential benefits are increased genetic variability, size-specific processes, and synergistic interactions between genetic variants. The particular cost or benefit of IGH in a specific case depends on the organism type and the origin of the IGH. While mosaicism easily arise by genetic changes in an individual, and will be the more common type of IGH, chimerism originates by the fusion of genetically distinct entities, and is expected to be substantially rare in most organisms. Potential conflicts and synergistic effects between different genetic lineages within an individual provide an interesting example for theoretical and empirical studies of multilevel selection.

Agminated acquired melanocytic nevi of the common and dysplastic type

We previously reported a single case of agminated acquired melanocytic nevi, consisting of a localized clustering of banal and atypical moles. We now report 4 more cases, confirming that the initial case was not an isolated finding. We examined the lesions clinically, with a dermoscope, with a Wood's light, and in 3 cases with UV photography so as to exclude nevus spilus from the differential diagnosis. The presence of an underlying dysplastic nevus syndrome phenotype in 4 of the 5 cases raises the possibility that agminated nevi arise as a consequence of postzygotic loss of heterozygosity and, thus, may represent a type 2 segmental manifestation of the atypical mole syndrome phenotype. Further studies of similar cases using microdissection techniques for analysis of loss of heterozygosity pattern are warranted.

Epidermolytic hyperkeratosis: a keratin 1 or 10 mutational event

Epidermolytic hyperkeratosis is an unusual type of ichthyosis. This inherited keratinization disorder is characterized clinically by erythema, blistering, and peeling shortly after birth. It may resolve and be replaced with thick scaling. It can lead to life-threatening complications, such as sepsis. Histologically, there is a hyperkeratosis and vacuolar degeneration. Genetically, this is an autosomal dominant disease with complete penetrance; however, 50% are spontaneous mutations. The clinical phenotype is a result of alterations in the gene(s) for keratin 1 and/or 10. We review this disorder and its therapy, which is mainly symptomatic with emollients and retinoids.

Somatic mosaicism and cancer: inference based on a conditional Luria-Delbrück distribution

Somatic mosaicism for mutations in disease-causing genes has been reported in several recent studies. Examples include hemophilia A, many skin disorders, and several cancers such as retinoblastoma and familial adenomatous polyposis. Many of these disorders require multiple mutations in order to express the disease phenotype. For example, two recessive mutations to the retinoblastoma locus are required to initiate retinoblastomal tumors. I develop a mathematical framework for somatic mosaicism in which two recessive mutations cause disease. With my framework, I analyse the following question: Given an observed frequency of cells with two mutations and an easily scored aberrant phenotype, what is the conditional frequency distribution of cells carrying one mutation and therefore susceptible to transformation by a second mutation? This question is important because a high frequency of carrier cells can cause genetic counselors to misdiagnose a mosaic as an inherited heterozygote carrier and because widespread mosaicism can lead to some germline transmission. As more data accumulate, the observed distribution of mosaics can be compared against my predicted distribution. These sorts of studies will contribute to a broader understanding of the distribution of somatic mutations, a central topic in the study of cancer.