Reduction of palmoplantar keratoderma Buschke-Fischer-Brauer locus to only 0.967 Mb

Is punctate palmoplantar keratoderma type 1 associated with malignancy? A systematic review of the literature

BACKGROUND

An association between punctate palmoplantar keratoderma type 1 (PPPK1) and malignancy has been proposed for decades. Some authors suggest that individuals with PPPK1 should undergo screening for various types of malignancies while others caution that an association is not well-established. In this systematic review, we summarized and evaluated the current evidence for a possible association between PPPK1 and malignancy.

METHODS

The review was conducted along PRISMA guidelines. The search used Embase, MEDLINE, Scopus, and the Human Gene Mutation Database up to March 2022. All studies reporting on individuals with the diagnosis of PPPK1 with or without history of malignancy were included. Two authors screened for eligible studies, extracted predefined data, and performed a quality assessment.

RESULTS

Of 773 studies identified, 45 were included. Most studies were reports on single families (24 of 45 studies) or multiple families (10 of 45 studies). The number of index cases with PPPK1 across all included studies was 280, and when family members reported with PPPK1 were added, a total of 817 individuals were identified. Overall, 23 studies reported on individuals with PPPK1 with a history of malignancy, whereas 22 studies reported on individuals with PPPK1 without a history of malignancy. Although the extracted data were not considered to be of sufficient quality to synthesize and answer our research question, the review did not confirm an association between PPPK1 and malignancy.

CONCLUSION

This review shows that there is a lack of well-designed studies on this topic to conclude whether individuals with PPPK1 have an increased risk of malignancy. Based on the present literature, however, we could not confirm an association between PPPK1 and malignancy and find it highly questionable if patients with PPPK1 should be offered surveillance for malignancies.

Nonsense mutations in AAGAB cause punctate palmoplantar keratoderma type Buschke-Fischer-Brauer

Punctate palmoplantar keratodermas (PPKPs) are rare autosomal-dominant inherited skin diseases that are characterized by multiple hyperkeratotic plaques distributed on the palms and soles. To date, two different loci in chromosomal regions 15q22-15q24 and 8q24.13-8q24.21 have been reported. Pathogenic mutations, however, have yet to be identified. In order to elucidate the genetic cause of PPKP type Buschke-Fischer-Brauer (PPKP1), we performed exome sequencing in five affected individuals from three families, and we identified in chromosomal region 15q22.33-q23 two heterozygous nonsense mutations-c.370C>T (p.Arg124(∗)) and c.481C>T (p.Arg161(∗))-in AAGAB in all affected individuals. Using immunoblot analysis, we showed that both mutations result in premature termination of translation and truncated protein products. Analyses of mRNA of affected individuals revealed that the disease allele is either not detectable or only detectable at low levels. To assess the consequences of the mutations in skin, we performed immunofluorescence analyses. Notably, the amount of granular staining in the keratinocytes of affected individuals was lower in the cytoplasm but higher around the nucleus than it was in the keratinocytes of control individuals. AAGAB encodes the alpha-and gamma-adaptin-binding protein p34 and might play a role in membrane traffic as a chaperone. The identification of mutations, along with the results from additional studies, defines the genetic basis of PPKP1 and provides evidence that AAGAB plays an important role in skin integrity.