autoimmune polyendocrinopathy candidiasis ectodermal dystrophy ( apeced ) is a rare autosomal recessive disease ( omim 240300 ) with a complex clinical phenotype discovered over decades . apeced is the first multiple autoimmune disease that has been shown to be caused by mutations of a single gene named autoimmune regulator gene ( aire ) , which maps to 21q22.3   and encodes a 55-kda protein that acts as a transcription regulator expressed in immune - related organs . immunologically , the disorder is characterized by lymphocytic infiltrate of target organs and appearance of serum autoantibodies against several defined tissue - restricted antigens , predicting or correlating with functional failure [ 3 , 4 ] . the variability of its clinical expression implies that diagnosis can often be challenging . since a prompt diagnosis is essential to prevent severe complications , clinicians should be aware of all symptoms and signs of suspicion . aim of this paper is to give an overview on the clinical presentation and diagnostic criteria of apeced . moreover , attention will be paid to the current knowledge on genotype - phenotype correlation . apeced usually presents in childhood , but new disease components may appear even in the fifth decade of life . clinical picture is generally characterized by a wide heterogeneity and the phenotype widely varies in the severity and in the number of components among affected subjects . this variability reflects the highly variable pattern of destructive autoimmune reactions toward different endocrine and non endocrine organs . chronic mucocutaneous candidiasis ( cmc ) , chronic hypoparathyroidism ( ch ) and addison 's disease ( ad ) , represent the clinical hallmark of the syndrome and the clinical diagnosis of apeced requires the presence of at least two of these three major components . cmc has been reported as the first sign to appear in most but not all series of reported patients . in fact , in a series of 23 iranian jewish patients only four had relatively mild oral , transient , candidiasis . it is often followed by ch , before the age of 10  yrs , and later by adrenal insufficiency . in addition to the classic triad ( cmc , ch , ad ) , the phenotype of apeced includes several endocrine and nonendocrine autoimmune manifestations , which in a few cases may also precede the classical triad . in fact , 10 of 91 finnish patients had one to three other components 0.114 years prior of the appearance of any of the major elements of the triad . within subjects with cmc , 21 patients had from one to six other components for 0.225 years before ch or ad appeared . cmc is a sign of the underlying immunodeficiency , thus being different in the pathogenesis from the multiple autoimmune manifestations of apeced . more severe cases include inflammation of most of the oral mucosa , hyperplastic cmc , and atrophic form with thin mucosa and leukoplakic areas . oesophageal and intestinal candidiasis may also occur and is characterized by abdominal pain , flatulence , and diarrhea . patients with long - lasting oral and/or esophageal candidiasis are at increased risk of esophageal squamous cell carcinoma . in the finnish series , 10.5% of patients over 25 years of age developed squamous cell carcinoma of the oral cavity or of the esophagus . this indicates that the carcinoma is not rare in these patients and , therefore , candidiasis should be aggressively treated with topical antifungals together with good oral hygiene . the critical mechanisms of the increased susceptibility to cmc in apeced patients are still poorly understood although autoantibodies to cytokines seem to be implicated in the pathogenesis . recently , a role of specific neutralizing autoantibodies against the th17-related cytokines il-22 and il-17f , and the concomitant loss of th17 and th22 cells , has been hypothesized in the pathogenesis of the cmc . on the other hand , it should be mentioned that it has been hypothesized that chronic candida infection may trigger an autoimmune disease by inducing a chronic inflammation with the persistence of high levels of cytokines . symptoms of hypocalcemia may be vague with muscle cramps , mild paraesthesia , and clumsiness for long - time before the diagnosis is made and , sometimes , hypocalcemia may precipitate during febrile illness presenting with grand - mal type seizures . candidate autoantigens previously linked to the development of hypoparathyroidism in apeced patients , as the calcium sensing receptor ( ca - s - r ) has not been confirmed as relevant autoantigen [ 4 , 1013 ] . recently , nalp5 ( natch leucine - rich repeat protein 5 ) has been identified as the target for autoimmune attack in the parathyroid cells   in the context of apeced but autoantibodies against this antigen are exceptionally rare in isolated hypoparathyroidism . adrenal insufficiency may be asymptomatic for long - time as well as patients can report fatigue , weight loss , and increased pigmentation of mucous membrane and skin . elevated plasma acth and/or renin together with low cortisol are the hallmarks of the disease . however , it should be highlighted that an increase in renin levels alone may be the first biochemical abnormality of ad , since the destructions of adrenal zona fascicualta and zona glomerulosa often are not simultaneous , the latter being the first layer targeted by the autoimmune attack . the majority of patients with apeced may display autoantibodies against 21-hydroxilase even years before the clinical onset of the disease . the detection of these antibodies calls for monitoring the adrenal function to prevent adrenal crisis . the spectrum of endocrinopathies associated with apeced in addition to ch and ad includes hypergonadotropic hypogonadism , which is generally present only in affected females , type 1 diabetes , autoimmune thyroid diseases , and pituitary defects . the occurrence of these manifestations is usually associated with a specific array of organ - specific autoantibodies that can appear quite before the overt clinical manifestation . the main ectodermal manifestations in apeced are dental enamel hypoplasia , pitted nail dystrophy , and alopecia . keratopathy , vitiligo , calcifications of the tympanic membranes , and rash with fever can also be present [ 7 , 17 ] . in young patients periodic maculopapular , morbilliform , or urticarial rash usually with fever can be part of the first manifestation and in most , appears before the age of 5 years . although the pathogenesis of ectodermal dystrophies seems to be autoimmune , no specific antibodies associated have been reported to date . ocular manifestations are keratopathy , dry eye , sublenticular cataract , iridocyclitis , retinal detachment and optic atrophy . among these , keratopathy can be a severe complication which , in the absence of appropriate treatment , may lead to blindness . furthermore , gastrointestinal autoimmunity in apeced may lead to autoimmune gastritis , autoimmune hepatitis , and intestinal disorders with chronic diarrhea alternating with obstipation . autoimmune hepatitis can vary from mild and self - limited to severe forms requiring treatment with immunosuppressants   and is characterized by the presence of peculiar immunological markers such as autoantibodies against cytochrome p450ia2 ( cyp ia2 ) , cyp2a6 , and aromatic l - aminoacid decarboxylase ( aadc ) [ 1921 ] . interestingly , the intestinal endocrine cells are also the targets of autoimmune attack , and , with this regard , it has been suggested that intestinal dysfunction can also be considered to be an endocrinopathy . gastrointestinal symptoms have been associated with the presence of autoantibodies against tryptophan hydroxylase ( tphabs ) . asplenia , tubulointerstitial nephritis , obstructive lung disease , vasculitis , sjgren 's syndrome , cutaneous vasculitis , hemolytic anemia , scleroderma , metaphyseal dysplasia , and celiac disease have also been reported to be associated with apeced [ 25 , 26 ] . autoantibodies directed against the potassium channel regulatory protein ( kcnrg ) , found in epithelial cells of terminal bronchioles , have been suggested as a marker for pulmonary disease in apeced patients . the autoimmune nature of renal destruction has been confirmed by examining biopsy samples and by determining antiproximal tubular autoantibodies [ 17 , 28 , 29 ] . acquired asplenia , presenting in up to 20% of apeced patients , results in impaired immune responses to encapsulated bacteria and is a serious risk factor for developing septicemia . asplenia can be suspected on the basis of the presence of peripheral blood smears of howell - jolly cells . six cases have been so far described with very similar clinical features of progressive limb - girdle myopathy in the context of apeced . myopathy with axial muscle involvement may also lead to a respiratory involvement and , eventually , life - threatening respiratory failure . to date , only 2 cases of encephalitis have been reported in the context of apeced one of them leading to a severe and life - threatening condition [ 32 , 33 ] . the overall mortality of patients with apeced varies widely on the basis of the clinical spectrum . the most dangerous autoimmune manifestations are fulminant necrotizing hepatitis , severe malabsorption , and tubulointerstitial nephritis . suboptimal hormonal substitution or inadequate management of addisonian crisis , may also increase the mortality risk . furthermore , patients with long - lasting oral candidiasis are at increased risk of esophageal squamous cell carcinoma . disease targeted therapy is not currently available and the treatment mainly relies on hormone replacement and caring for clinical symptoms . so far , immunosuppressive therapy has only been used for potentially fatal disease such as hepatitis , nephritis , or severe malabsorption . new examples of immunomodulatory treatment of aire knockout mouse both targeting t and b cells [ 34 , 35 ] lend hope that such strategies could also be useful in the future for these patients . more recently , a monoclonal antibody against b cells , rituximab , has been successfully used to treat pulmonary disease in apeced patients , raising the hope of applying it to all patients with apeced . the diagnosis of apeced is primarily based on the presence of two of the three most common clinical features : cmc , ch , and ad . the presence of only one component is sufficient for the diagnosis if a sibling is affected . however , the early clinical picture can be dominated by one of the minor components or the presence of only one major component and , in these circumstances , apeced can be misdiagnosed . therefore , in children the presence of a minor component should prompt to carefully investigate for other symptoms . candidiasis in childhood ( and even more in adolescence or adulthood ) is often underestimated as an initial symptom of a more complex disease . in a recent survey on 24 patients affected by apeced , mazza et al .   underlined the considerable delay between the appearance of the first symptoms of apeced and the time of diagnosis of the disease with a mean diagnostic delay of about 10 years . the identification of causal genetic mutations in aire can confirm the diagnosis and may be helpful in those cases with atypical presentation . in about 95% of patients , autoantibodies also constitute important diagnostic markers and may be in some cases predictive of a specific disease manifestation as detailed in table 1 [ 3 , 4 , 1315 , 1921 , 24 , 2628 , 3743 ] . recently , neutralizing autoantibodies for type 1 interferons ( inf ) ( ifn- and ifn- ) have been highly correlated with aire deficiency , regardless of the aire genotype , apeced features and duration . therefore , they appear as a precious diagnostic tool to screen patients with unusual clinical manifestations of apeced instead of a more expensive and unjustified aire sequencing [ 44 , 45 ] . in particular , anti - ifn- antibodies seem to appear very early in life and their presence virtually confirms the diagnosis [ 45 , 46 ] . therefore , these autoantibodies have been recently included in the new diagnostic criteria for the diagnosis of apeced as reported by husebye et al .   and shown in table 2 . as already mentioned , apeced is caused by mutations in the transcriptional regulator , aire . aire is a crucial factor in the central tolerance for the right development of self - tolerance promoting clonal - deletion of self - reactive thymocytes . within thymic medullary epithelial cells ( mtecs ) , aire induces the expression of a broad repertoire of peripheral tissue antigens ( ptas ) normally expressed in the periphery , eventually leading to the deletion of t - autoreactive cells [ 2 , 47 ] . therefore , the absence of aire results in impaired clonal deletion of self - reactive thymocytes , which attack a variety of organs . moreover , there is now strong evidence for aire expression in peripheral tissues even if these levels are significantly lower than in thymic stromal cells . the lineage of extrathymic aire expressing cells have been described as both myeloid [ 4852 ] and epithelial   in particular in lymph node , fetal liver , and appendix tissues . although apeced is rare , it is relatively more frequent in some populations ( 1  :  9000 in the iranian jews , 1  :  25000 in finns [ 5 , 54 ] , and 1  : 14.400 in sardinians ) . it is also quite frequent in norway ( 1  :  90.000 )   and other regions of italy . even though the most frequent mode of inheritance is autosomal recessive , an italian family with apeced harbored a missense ( g228w ) mutation in the exon 6 in heterozygosity , indicating a dominant pattern of inheritance . so far , over 70 different mutations of the aire gene have been documented in apeced patients   ( figure 1 ) . r257x is the most common mutation among finnish and other european patients [ 5961 ] , 10941106  del113 ( or 967979  del13  bp ) is the most common mutation in british , irish , north america [ 64 , 65 ] , and norwegian patients , and the y85c is the only mutation found among iranian jews . in italy apeced shows an increased prevalence in various regions , in particular in sardinia , apulia , and venetian area . moreover , both in sardinia and apulia peculiar mutations of aire have been identified : the mutation r139x on exon 3 in sardinia [ 21 , 67 ] and the mutations w78r and q358x on exon 2 and 9 , respectively , in apulia . in the veneto region , aire mutations ( r257x and 979  del-13  bp on exon 6 and 8 , respectively ) were different from the other italian regions but similar to that identified in finnish and anglo - saxon patients . among sicilian patients , the typical mutation is r203x on exon 5   but two novel mutations have been recently identified ( s107c and q108fs on exon 3 ) . although not showing a typical gene mutation , the patients from campania exhibit a high frequency of mutations in the exon / intron 1 junction . no aire gene mutation specific to calabria has been found in patients with the disease . apeced is characterized by a wide variability of the clinical expression . in the largest reported series of 91 finnish patients , a wide variation of the clinical phenotype and of the clinical course of apeced later on , many other authors confirmed this phenotypic heterogeneity among several populations [ 54 , 55 , 57 , 60 , 63 , 65 , 69 , 71 , 73 ] . in the majority of these studies , in fact , the iranian jewish patients ' phenotype and genotype are peculiar of their population and differ markedly from others . there is also evidence for a different sex prevalence of hypergonadotropic hypogonadism   and hypoparathyroidism . in fact , this mutation seems to elicit an unusually high risk of autoimmune thyroiditis ( at ) , while showing a lower penetrance for apeced . noteworthy , the clinical expression of the disease can be widely different even between siblings carrying the same mutation . such heterogeneity strongly suggests that disease - modifying genes , environmental factors , as well as immune system dynamics may play a role in modulating clinical expression of the syndrome . recent studies revealed effects of additional genetic loci , in particular the human leukocyte antigen ( hla ) complex on certain disease manifestations of apeced . associations with specific hla haplotypes have been found for components like alopecia , ad , and type 1 diabetes in patients with apeced [ 76 , 77 ] . these haplotypes are those associated with the common , non - apeced - related forms of that specific disorder . however , only a weak association has been observed between the hla type and autoantibody specificities in apeced patients , suggesting that in apeced the hla alleles do not have a strong influence on autoantibody formation per se .   along with the central tolerance network , which is primarily involved in pathogenesis of apeced , several other peripheral mechanisms are capable of contributing to the control and regulation of the immune system . these factors are involved in the maintenance of the homeostasis of peripheral tolerance of residual autoreactive clones , which escape negative selection within the thymus and play a significant role in preventing or minimizing reactivity to self - antigens . the peripheral tolerance recognizes , as possible mechanisms , the induction of functional anergy with inactivation of self - reactive t cells , deletion of autoreactive clones by apoptosis through interaction of fas / fasl , and the suppressive action of regulatory t lymphocytes ( treg ) . an additional mechanism involved in controlling reactivity to self engages in the periphery is natural killer ( nk ) cells activity . therefore , alterations dependant on one of the peripheral tolerance mechanisms   could contribute to the wide variability of apeced 's clinical expression . to date , there are only few studies on the functionality of these immunological tolerance mechanisms in patients with apeced . a decrease of cd4+cd25 + tregs in both adults and children with apeced has been reported [ 75 , 80 ] . however , the reduction in circulating tregs might also be secondary to the chronic fungal infection in these individuals and , therefore , their pathogenetic role in the disease still needs to be clarified . recently , several genetic , environmental , and molecular factors potentially implicated in the phenotypic variability of apeced have been investigated in two siblings affected with apeced . they were characterized by an extremely different phenotypic expression despite an identical aire ( ivs1 + 1 g > c ; ivs1 + 5delg ) . in particular , the younger sister had a mild form of the syndrome while the older male developed a severe phenotype exhibiting an accelerated phase involving parathyroid , thyroid , oral mucosa , skin , liver , adrenal glands , bowel , and stomach culminating in a life - threatening posterior encephalopathy syndrome ( pres ) . pres is a neurological condition characterized by acute encephalopathy with specific radiological findings , rarely reported in children . the pathogenesis is still unclear , however there is evidence relating pres with autoimmune diseases or use or use of immunosuppressants .   the exposure to infectious agents as rubella , epstein barr virus , cytomegalovirus , toxoplasma , varicella zoster virus , parvovirus b19 , herpes simplex virus , and parainfluenza virus was ruled out as trigger factor . mechanisms of peripheral tolerance ( fas - induced apoptosis , number of tcd4+cd25 + regulatory cells , and natural killer activity ) and hla haplotype were compared in the two sibs and any significant difference was found . however , the chance is large that the two sibs differ in their genetic make - up and this could explain the difference in clinical course despite the same aire mutation . as for other mendelian disorders , the interplay between multiple genetic , epigenetic , and environmental factors certainly play a role . diagnosis of apeced can be challenging and , although symptoms usually appear during the childhood , the diagnosis can be delayed up to the second decade of life . the reasons of difficulty in early recognition of these patients also rely on the heterogeneity of clinical spectrum which implies that genetic and environmental factors , other than aire , modulate the clinical expression . moreover , it should be mentioned that the timing of the appearance of the individual disorders profoundly varies during the childhood , thus implying that most patients may develop new disease components in the 3rd5th decade of life . a better understanding of these factors involved in the clinical expression of the disease could certainly improve current knowledge on the pathogenesis of apeced and help in identifying novel therapeutic targets .
autoimmune polyendocrinopathy candidiasis ectodermal dystrophy ( apeced ) is a rare autosomal recessive disease , caused by mutations of a single gene named autoimmune regulator gene ( aire ) which results in a failure of t cell tolerance within the thymus . 
 chronic mucocutaneous candidiasis , chronic hypoparathyroidism , and addison 's disease are the hallmarks of the syndrome . 
 apeced is also characterized by several autoimmune endocrine and nonendocrine manifestations , and the phenotype is often complex . moreover , even though apeced is a monogenic disease , its clinical picture is generally dominated by a wide heterogeneity both in the severity and in the number of components even among siblings with the same aire genotype . 
 the variability of its clinical expression implies that diagnosis can be challenging , and a considerable delay often occurs between the appearance of symptoms and the diagnosis . since a prompt 
 diagnosis is essential to prevent severe complications , clinicians should be aware of all symptoms and signs of suspicion . 
 the aim of this paper is to give an overview on the clinical presentation and diagnostic criteria of apeced and to focus on current knowledge on genotype - phenotype correlation .