A rare, genetic, chronic, recurrent, slowly progressive, epidermal disease characterized by small, sterile, pustular eruptions, involving the nails and surrounding skin of the fingers and/or toes, which coalesce and burst, leaving erythematous, atrophic skin where new pustules develop. Onychodystrophy is frequently associated and anonychia and osteolysis are reported in severe cases. Local expansion (to involve the hands, forearms and/or feet) and involvement of mucosal surfaces (e.g. conjunctiva, tongue, urethra) may be observed.

Familial periodic fever (FPF) is an autoinflammatory disorder characterized by recurrent fever with localized myalgia and painful erythema. Febrile attacks may last 1 or 2 days but often last longer than 1 week. Arthralgia of large joints, abdominal pain, conjunctivitis, and periorbital edema are common features. During attacks, painless cutaneous lesions may develop on the trunk or extremities and may migrate distally (review by Drenth and van der Meer, 2001).

Spondyloarthropathy (SpA), one of the commonest chronic rheumatic diseases, includes a spectrum of related disorders comprising the prototype ankylosing spondylitis (AS), a subset of psoriatic arthritis (PsA), reactive arthritis (ReA), arthritis associated with inflammatory bowel disease, and undifferentiated spondyloarthropathy (Miceli-Richard et al., 2004). These phenotypes are difficult to differentiate because they may occur simultaneously or sequentially in the same patient. Studies have suggested that a predominant shared component, including HLA-B27, predisposes to all phenotypic subsets, and that these subsets should be considered as various phenotypic expressions of the same disease (Said-Nahal et al., 2000, Said-Nahal et al., 2001). Braun and Sieper (2007) provided a detailed review of ankylosing spondylitis, including clinical features, pathogenesis, and management. Genetic Heterogeneity of Susceptibility to Spondyloarthropathy Additional susceptibility loci for spondyloarthropathy have been identified on chromosome 9q31-q34 (SPDA2; 183840) and chromosome 2q36 (SPDA3; 613238).

Immunodeficiency-85 and autoimmunity (IMD85) is an autosomal dominant immunologic disorder characterized by onset of atopic eczema and recurrent respiratory infections in the first decade of life. Affected individuals also develop autoimmune enteropathy with vomiting, diarrhea, and poor overall growth. More variable features may include autoimmune oligoarthritis, interstitial pneumonitis, and EBV viremia. Laboratory studies show hypogammaglobulinemia and abnormal T-cell function, consistent with a combined immunodeficiency (Keskitalo et al., 2019).