Prolidase deficiency, a rare inborn error of immunity, clinical phenotypes, immunological features, and proposed treatments in twins

Abstract

Background Prolidase deficiency (PD) is an autosomal recessive inborn multisystemic disease caused by mutations in the PEPD gene encoding the enzyme prolidase D, leading to defects in turnover of proline-containing proteins, such as collagen. PD is categorized as a metabolic disease, but also as an inborn error of immunity. PD presents with a range of findings including dysmorphic features, intellectual disabilities, recurrent infections, intractable skin ulceration, autoimmunity, and splenomegaly. Despite symptoms of immune dysregulation, only very limited immunologic assessments have been reported and standard therapies for PD have not been described. We report twin females with PD, including comprehensive immunologic profiles and treatment modalities used. Case presentation Patient 1 had recurrent infections in childhood. At age 13, she presented with telangiectasia, followed by painful, refractory skin ulcerations on her lower limbs, where skin biopsy excluded vasculitis. She had typical dysmorphic features of PD. Next-generation sequencing revealed pathogenic compound heterozygous mutations (premature stop codons) in the PEPD gene. Patient 2 had the same mutations, typical PD facial features, atopy, and telangiectasias, but no skin ulceration. Both patients had imidodipeptiduria. Lymphocyte subset analysis revealed low-normal frequency of Treg cells and decreased frequency of expression of the checkpoint molecule CTLA-4 in CD4+ TEM cells. Analysis of Th1, Th2, and Th17 profiles revealed increased inflammatory IL-17+ CD8+ TEM cells in both patients and overexpression of the activation marker HLA-DR on CD4+ TEM cells, reflecting a highly activated proinflammatory state. Neither PD patient had specific antibody deficiencies despite low CD4+CXCR5+ Tfh cells and low class-switched memory B cells. Plasma IL-18 levels were exceptionally high. Conclusions Immunologic abnormalities including skewed frequencies of activated inflammatory CD4+ and CD8+ TEM cells, decreased CTLA-4 expression, and defects in memory B cells may be a feature of immune dysregulation associated with PD; however, a larger sample size is required to validate these findings. The high IL-18 plasma levels suggest underlying autoinflammatory processes.

Prolidase Deficiency Causes Spontaneous T Cell Activation and Lupus-like Autoimmunity

“…In the absence of prolidase, both CD4 and CD8 effector T cells accumulate, whereas peripheral B cell numbers are normal. Consistent with our findings in the Pepd −/− mice, immune profiling of two prolidase-deficient patients has described normal B cell numbers, accompanied by an increase in CD8 effector T cells with an inflammatory phenotype in one of these patients ( 48 ).…”

Genetic/Environmental Contributions and Immune Dysregulation in Children with Atopic Dermatitis

“… 144 PEPD encodes prolidase, which metabolizes proline-containing proteins including collagen. 124 SPINK5 encodes the SP inhibitor LEKTI, thereby modulating skin desquamation. 145 , 146 Finally, DSG1 and DSP encode desmosome components that contribute to epidermal structure and integrity.…”

“…These conditions and their known culprit genes include Hyper IgE syndrome (STAT3, DOCK8), CARMIL2 deficiency (CARMIL2), Omenn syndrome (RAG1, RAG2), Netherton syndrome (SPINK5), Wiskott-Aldrich syndrome (WAS), adenosine deaminase severe combined immunodeficiency (ADA-SCID) (ADA), immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome (FOXP3), CARD11-associated atopy with dominant interference of NF-κB signaling (CADINS) disease (CARD11), congenital disorders of glycosylation (PGM3), prolidase deficiency (PEPD), severe dermatitis, multiple allergies, and metabolic wasting (SAM) syndrome (DSG1, DSP), and growth hormone insensitivity (GHI) syndrome with immunodeficiency (STAT5B). [116][117][118][119][120][121][122][123][124][125][126][127][128][129] Recently, GoF STAT6 variants have been associated with a novel autosomal dominant allergic disorder featuring early-onset allergic immune dysregulation with widespread refractory AD, hypereosinophilia with eosinophilic esophagitis, high serum IgE, food allergies, and brain vascular anomalies. 130 Although rare, these genetic disorders should be considered in the differential diagnosis of AD, especially in patients where the constellation of findings exceeds atopy.…”

Atopic manifestations of inborn errors of immunity

“…FLG and DSG1 are marked in italics, as they are not necessarily associated with IEI but are monogenic defects supporting the pathogenic category. We have grouped thymic development disorders and decreased T cell repertoire diversity [4 ▪ ,5,6 ▪ ,26,28–41].…”