A Polygenic Risk Score for Predicting Racial and Genetic Susceptibility to Prurigo Nodularis

Prurigo nodularis (PN) is an understudied inflammatory skin disease characterized by pruritic, hyperkeratotic nodules. Identifying the genetic factors underlying PN could help to better understand its etiology and guide the development of therapies. In this study, we developed a polygenic risk score that predicts a diagnosis of PN (OR = 1.41, P = 1.6 × 10-5) in two independent and continentally distinct populations. We also performed GWASs, which uncovered genetic variants associated with PN, including one near PLCB4 (rs6039266: OR = 3.15, P = 4.8 × 10-8) and others near TXNRD1 (rs34217906: OR = 1.71, P = 6.4 × 10-7; rs7134193: OR = 1.57, P = 1.1 × 10-6). Finally, we discovered that Black patients have over a two-times greater genetic risk of developing PN (OR = 2.63, P = 7.8 × 10-4). Combining the polygenic risk score and self-reported race together was significantly predictive of PN (OR = 1.32, P = 4.7 × 10-3). Strikingly, this association was more significant with race than after adjusting for genetic ancestry. Because race is a sociocultural construct and not a genetically bound category, our findings suggest that genetics, environmental influence, and social determinants of health likely affect the development of PN and may contribute to clinically observed racial disparities.

Treatment of idiopathic prurigo nodularis in Taiwanese patients with low-dose thalidomide

Prurigo nodularis is an intensely pruritic dermatosis characterized by lichenified and excoriated papules and nodules. The course of prurigo nodularis is often chronic, and some patients respond very poorly to the standard therapeutic modalities. Because the pathogenesis of this disease remains obscure, the treatment of prurigo nodularis can be disappointing and frustrating for both the patients and physicians. Thalidomide, a tumor necrosis factor-alpha antagonist, has been suggested as an alternative treatment option for recalcitrant prurigo nodularis. In the past, the regimen for treatment of prurigo nodularis often required thalidomide at 200 mg/day. We recruited patients with intractable prurigo nodularis and treated them with low-dose thalidomide. Six patients with idiopathic prurigo nodularis were successfully treated with low-dose thalidomide (50-100 mg/day) without clinical development of peripheral neuropathy. In summary, our preliminary results suggest that low-dose thalidomide may be a safe and effective treatment option for patients with recalcitrant idiopathic prurigo nodularis.

Evidence that thalidomide modifies the immune response of patients suffering from actinic prurigo

BACKGROUND

Actinic prurigo (AP) is a photodermatosis with a restricted ethnic distribution, mainly affecting Mestizo women (mixed Indian and European). The lesions are polymorphic and include macules, papules, crusts, hyperpigmentation and lichenification. Thalidomide, an effective immunomodulatory drug, was first used successfully to treat AP in 1973. In this work we describe the effect that thalidomide had on TNF-alpha sera levels and on IL-4- and IFN gamma (IFNgamma)-producing lymphocytes of actinic prurigo (AP) patients.

METHODS

Actinic prurigo patients were analyzed before and after thalidomide treatment. The percentage of IL-4+ or IFNgamma+ CD3+ lymphocytes was analyzed in eight of them by flow cytometry. TNFalpha in sera was measured by ELISA in 11 patients.

RESULTS

A direct correlation was observed between resolution of AP lesions and an increase in IFNgamma+ CD3+ peripheral blood mononuclear cells (P < or = 0.001) and a decrease in TNFalpha serum levels (no statistical difference). No IL-4+ CD3+ cells were detected.

CONCLUSIONS

Our findings confirm that AP is a disease that has an immunological component and that thalidomide clinical efficacy is exerted not only through inhibition of TNFalpha synthesis, but also through modulation of INFgamma-producing CD3+ cells. These cells could be used as clinical markers for recovery.

Actinic prurigo: Clinical features and HLA associations in a Canadian Inuit population

BACKGROUND

Actinic prurigo (AP) is an idiopathic familial photodermatitis. AP of the Inuit is rarely reported and poorly characterized.

OBJECTIVE

Our purpose was to examine the clinical features and HLA associations of AP in an Inuit population.

METHODS

Thirty-seven Inuit subjects with AP were administered a questionnaire and underwent a cutaneous examination. Other causes of photosensitivity were excluded. HLA class I typing was performed by polymerase chain reaction and sequence-specific primers and class II typing by polymerase chain reaction and sequence-specific oligonucleotide probes.

RESULTS

Subjects were 81.1% female, 67.6% had a family history of photosensitivity, and all experienced seasonal variation. The average age at onset of photosensitivity was 29 years, and only 27% had a trend toward improvement in photosensitivity. Involvement of eyes and nonexposed skin was reported in 62.2% and 18.9% of subjects, respectively. Physical examination revealed involvement of the face (64.9%), lip (32.4%), ear (13.5%), and dorsal aspect of the hand (24.3%). HLA-DRB1*14 was present in 51.2% of subjects and 26.2% of controls (P =.022, odds ratio = 2.975). This is a previously unreported HLA association.

CONCLUSION

AP in the Inuit is a seasonal, pruritic photodermatitis, often commencing in adulthood and worsening over time. A novel association with HLA-DRB1*14 has been discovered. Overall, this novel HLA association, the absence of HLA associations previously reported in non-Inuit populations, and clinical distinguishing features support the concept that AP in the Inuit may have a distinct immunopathogenic basis that translates into a different phenotype. It also raises the question of whether AP in the Inuit is a distinct photosensitivity disorder specific to this group that has been genetically isolated because of geographic and cultural seclusion.

Major gene segregation of actinic prurigo among North American Indians in Saskatchewan

Actinic prurigo is an idiopathic, familial photodermatosis seen especially in American Indians. Segregation analysis was performed on 12 Saskatchewan pedigrees with American Indian ancestry, comprising a total of 1,148 individuals, ascertained via probands diagnosed with actinic prurigo. Although a high degree of familial aggregation has been noted in the past and dominant inheritance has been suggested, no formal segregation analysis has been attempted. Actinic prurigo has a variable age of onset and, therefore, age at the time of censoring must be taken into account in the analysis. However, as these ages of 57% of the unaffected individuals were missing, an algorithm was devised to impute the missing ages from known birth years in the family based on the age differences among relatives and spouses. Using these imputed ages, simple dominant inheritance with incomplete penetrance and a single age of onset distribution was found. The method for imputing the ages at examination was evaluated, as was the correction for ascertainment, by using alternative methods and comparing the results. Regardless of the method used, a dominant mode of inheritance without any multifactorial component remained the best hypothesis.

A case of actinic prurigo in Thailand

Actinic prurigo is a separate entity from the polymorphous light eruption that affects American Indians. It has been reported mainly from North and South America, with only few reported cases from Britain or Asia. We report a case of actinic prurigo in a Thai girl who showed cheilitis and pruritic papules on exposed areas for three years. We were able to induce populovesicular lesions by three consecutive irradiations with 100 J/cm2 UVA and 2 minimal erythematous dose of UVB. However, three weeks after irradiation, a prurigo papule developed at the UVB irradiated site.

Further evidence of the role of HLA-DR4 in the genetic susceptibility to actinic prurigo

BACKGROUND

Actinic prurigo (AP) is triggered by sun exposure. Its prevalence in Mexicans seems to be particularly high, which suggests a genetic susceptibility.

OBJECTIVE

Our purpose was to determine the role of major histocompatibility complex (MHC) genes in the genetic susceptibility to AP.

METHODS

Fifty-six Mexican Mestizo patients with AP underwent serologic typing for HLA class I and class II antigens. Class II MHC genes were also studied by DNA analysis. Findings in patients were compared with 100 ethnically matched healthy controls.

RESULTS

We found that 92.8% of patients with AP were HLA-DR4 positive (corrected p = 0.002; odds ratio [OR] = 10.1). The class I antigens HLA-A28 and HLA-B39 (B16) were also significantly increased (p < or = 0.000001, OR = 20.9 and p = 0.0001, OR = 6.7, respectively) compared with normal controls. Allele-specific oligonucleotide DR4 subtyping showed that 80.7% of HLA-DR4+ patients with AP were also positive for the DRB1*0407 allele.

CONCLUSION

These results confirm the role of HLA-DR4 (DRB1*0407) in the genetic susceptibility to AP and raise the possibility of a role for class I MHC antigens HLA-A28 and B16 in Mexican patients.

Treatment of actinic prurigo in Chimila Indians

BACKGROUND

Actinic prurigo has a high prevalence in women of child-bearing age. Its treatment has been, among others, with thalidomide. To avoid the deleterious effects of this drug on the embryo, therapeutic alternatives have been sought. Among these, tetracycline and vitamin E have been investigated as to their influence on the symptoms of actinic prurigo. Both these drugs affect superoxide radicals that are thought to be involved in the pathogenesis of actinic prurigo.

MATERIALS AND METHODS

Patients (Chimila Indians with a high prevalence of actinic prurigo) received either (a) tetracycline, 500 mg three times daily, for 6 months, or (b) vitamin E, 100 IU daily, for 6 months. The patients were seen once monthly. There were eight patients in each group.

RESULTS

Both drugs used were effective. Pruritus was remarkably improved by either treatment. None of the side effects were severe enough to lead to interruption of treatment, but the observation period posttreatment was relatively short, 4 months for tetracycline and 2 months for vitamin E. The improvement occurred in spite of the continuation of extensive exposure to the sun.

CONCLUSIONS

Tetracycline and vitamin E are efficacious in relieving the pruritus of actinic prurigo. Preliminary trials of a combination treatment with these two drugs is a new avenue which has shown in preliminary trials to yield synergistic effects which might allow the dosage of tetracycline to be reduced.

HLA-DR4 may determine expression of actinic prurigo in British patients

Human leukocyte antigen (HLA) associations have been reported in Amerindian patients with actinic prurigo. To determine if similar associations are present in the British Caucasoid population with actinic prurigo, 26 patients underwent serological typing for HLC Class I and II antigens. DNA analysis by both sequence-specific priming and group-specific amplification with single-stranded oligonucleotide probe hybridization was used to confirm the DR and DQ typing and to perform DR4 subtyping. All patients were DR4 positive, and 25 of 26 patients were DQ7 positive. DR4 subtyping revealed 12 of 20 patients tested to be DRB1*0407. A nonsignificant association was also found with HLA B55 that is in linkage disequilibrium with DRB1*0407. No HLA associations were found in 25 British Caucasoid patients with polymorphic light eruption. DRB1*0407 is rare in European Caucasoids without actinic prurigo, and HLA-DR4 may have an important role in determining expression of this disease.

Follicular cheilitis. A distinctive histopathologic finding in actinic prurigo

Actinic prurigo (AP), a chronic skin disease caused by an abnormal reaction to sunlight, is commonly associated with cheilitis and conjunctivitis. Characteristic ethnic, genetic, environmental (occurs at high altitudes, above 1,500 m), clinical, and histopathologic features have been reported. AP occurs in American Indians of Canada and the United States and most commonly in Latin American countries, where Mestizos (mixed ancestry) are predominantly affected. The present study investigates AP involving the lips, where it is characterized by a dense lymphocytic infiltrate, often with well-formed lymphoid follicles; the latter feature we refer to as "follicular cheilitis" (FC). The histopathologic findings of FC are characteristic of and helpful in diagnosing actinic prurigo involving the lips.

Histopathology of actinic prurigo

Actinic prurigo (AP) is an idiopathic familial photodermatosis seen in American Indians. We report on 17 patients; 16 had dermatitis and one had actinic cheilitis. Ten patients had acute dermatitis and six had chronic dermatitis. The histologies of acute AP and polymorphous light eruption (PLE; limited concept) are eczematous and indistinguishable. Both show spongiosis, superficial (and sometimes deep) perivascular lymphocytic infiltrates, and papillary dermal edema. Both also show vacuolar degeneration of the basal layer. In contrast, the chronic lichenified AP lesions are associated with marked hyperkeratosis, acanthosis, elongation of the rete ridges, and tissue repair. The large lymphoid germinal centers in the lamina propria are the main features of the lip histology. Seven biopsies were positive in the basal membrane zone on direct immunofluorescent testing, four were negative, and one was inconclusive. IgM was present in six and C3 in two. These immunofluorescent results are probably not significant. Immunofluorescent testing of the lip was negative. Although it is not possible to distinguish acute AP from PLE histologically, it is possible to differentiate the two conditions when chronic AP changes are present.

Patch testing in actinic prurigo

42 out of 93 Saskatchewan Indians (32 female (F) and 10 male (M] with actinic prurigo were patch tested to standard series allergens between 1983 and 1987. Positive reactions were most frequently seen with nickel (3F:2M) and colophony. All 3 positive patch tests to colophony were in males. The same patients were also patch tested to extracts of 21 Saskatchewan plants and 3 Hollister-Stier plant extracts. Only 1 male and 2 females had positive patch tests. None of these 3 had rashes on the eyelids, behind the ears or under the chin. We conclude that plant contact dermatitis is unlikely to be mistaken for actinic prurigo in Saskatchewan.

Actinic prurigo of the lower lip. Review of the literature and report of five cases

Actinic prurigo (AP) is a chronic, familial, photodermatitis that primarily affects American Indians. It is more prevalent in young females and may be evident clinically as a pruritic lower lip cheilitis that typically does not respond to conventional therapy. Other clinical features associated with AP include conjunctivitis, alopecia of the eyebrows, and formation of pterygia. The histologic features of AP have been described as nonspecific. We are presenting five cases of AP in which the major clinical manifestation was a pruritic, unsightly lower lip cheilitis. All of our patients were American Indians. Three patients were from the same family. The youngest patient was 10 years old and the oldest was 69 years old. All five cases were characterized histologically by numerous germinal centers within the lamina propria and a dense perivascular plasma cell infiltrate. In four of the five cases, there was a moderate to dense infiltrate of eosinophils. All five patients had been generally unresponsive to conventional therapy. With the exception of the youngest patient, all had had the disease for at least several years. One patient, now deceased, had the lower lip lesion surgically removed for cosmetic reasons. To our knowledge, this is the first report in the dental literature that describes the clinical and histologic features of AP of lower lip.