Type I Polyglandular Autoimmune Syndrome 

Polyglandular autoimmune (PGA) syndromes (otherwise known as polyglandular failure syndromes) are constellations of multiple endocrine gland insufficiencies. Other descriptive terminologies, such as autoimmune polyendocrine syndrome (APS), also are used in the literature. In the classification of these syndromes, Roman numerals (eg, I and II) and Arabic numbers (eg, 1 and 2) have been variably used in the literature. For the purpose of consistency in this article, the term PGA and Roman numerals will be used.

Essentially, 2 types of PGA exist, type I and the more common type II, also known as Schmidt syndrome. A third type (type III), which occurs in adults, has been described. Type III does not involve the adrenal cortex, but it includes 2 of the following: thyroid deficiency, pernicious anemia, type 1A diabetes mellitus, vitiligo, and alopecia. Other disorders also have been described in association with the PGA syndromes; pulmonary hypertension in association with PGA syndrome type II (PGA-II) is one example.^[1]

Historically, the interest in these syndromes began in the 19th century and essentially focused on the adrenal cortex. In 1849, Thomas Addison first described the clinical and pathologic features of adrenocortical failure in patients who also appeared to have coexisting pernicious anemia. Between 1849 and 1980, geneticists, immunologists, and endocrinologists generated a wealth of new information concerning the pathogenesis of the PGA syndromes and their component disorders.

In 1929, Thorpe and Handley recognized the association of mucocutaneous candidiasis with glandular failure, and case reports and case series have since appeared in the international literature. In 1981, Neufeld and colleagues distinguished 2 major PGA syndromes, and other authors subsequently began to add to our knowledge of these conditions.^[2] In 2004, Eisenbarth and Gottlieb extended the discussion on the classification of these syndromes.^[3] While they acknowledged the system that was adopted by the so-called splitters, dividing the syndromes into 4 subtypes (I, II, III, IV), Eisenbarth and Gottlieb recommended the system adapted by the "lumpers." The latter system "lumps" the syndromes into just 2 types, I and II. Finally, according to Eisenbarth and Gottlieb, the term polyendocrine is a misnomer, because these syndromes include a number of nonendocrine disorders.

PGA-I, also known as autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) or as Whitaker syndrome, is associated with candidiasis, hypoparathyroidism, and adrenal failure^[4] (although PGA-I without mucocutaneous candidiasis has been reported in an adolescent^[5] ). A syndrome with these features was first described in 1946. It is a rare disorder, with sporadic autosomal recessive inheritance.

The evidence supporting the autoimmune etiology of polyglandular autoimmune (PGA) syndrome, type I, is based on the presence of chronic inflammatory infiltrates composed mainly of lymphocytes in the affected organs and on the presence of autoantibodies reacting to target tissue – specific antigens. The antibodies are believed to occur as a result of a breakdown in normal immunologic tolerogenesis or as a consequence of immunization with an environmental agent that has a similar antigenic molecular structure to a self-antigen.

The 3 main types of autoantibodies are directed to the surface receptor molecules, intracellular enzymes, and secreted proteins, such as hormones. Their pathogenic relevance is still unclear, and even measuring levels of these autoantibodies against endocrine glands or their components does not appear to be useful, because such antibodies may persist for years without the patient developing endocrine failure. Their primary function is to differentiate autoimmune causes and infectious/iatrogenic causes of endocrine insufficiency.

With regard to genetic susceptibility, PGA-I is unique among autoimmune endocrine disorders, because it has no HLA antigen association. However, an increased frequency of HLA-A28 and HLA-A3 has been documented in PGA-I, more so than in normal controls. The genetic locus responsible for the disease has been localized to the short arm of chromosome 21 near markers D21s49 and D21s171 on band 21p22.3. A Finnish study concluded that the mutation R257X is responsible for 82% of cases.^[6]

A monogenic mutation of AIRE (autoimmune regulator), which codes for a putative transcription factor featuring 2 zinc motifs, is believed to be the likely pathogenic paradigm for PGA-I.^[7]

Studies on young, thymectomized mice have contributed significantly to the understanding of the pathophysiology of PGA-I, as neatly illustrated by Eisenbarth and Gottlieb in a 2004 review article.^[3]

Frequency

United States

In North America, polyglandular autoimmune (PGA) syndrome, type I, is extremely rare, and only scattered US case reports have been published. Most of the published literature has come from Europe, where the disease clusters in certain populations (see International frequency, below). Frequency, therefore, is not well documented in the United States; the mixed ethnic makeup of the US population may explain the low rate of case clustering. The 2 largest case series from North America were published by Neufeld and colleagues in 1981 and by Heino and coauthors in 1999.^{[2, 8]} In the latter report, 16 patients were described, including 13 white patients, 1 Hispanic individual, 1 Middle Eastern patient, and 1 Asian person.

International

Polyglandular autoimmune (PGA) syndrome, type I, is a very rare disorder; it clusters in certain homogeneous ethnic populations due to consanguineous marriages and/or clustering of descendants of common family founders. These populations include special groups of Finns, Sardinians, and Iranian Jews. Less frequent clustering has been reported from northern Italy, northern Britain, Norway, and Germany. Scattered case reports from various countries around the world have been published. The highest number of patient groups has notably been reported in Finland, in successive case series over the last few decades. The prevalence of PGA-I in Finland has been estimated to be 1 case per 25,000.^[6] Known frequencies in other ethnic groups include 1 case per 14,400 in Sardinians and 1 case per 9,000 in Iranian Jews.^{[9, 10]}

Mortality/Morbidity

The mortality and morbidity associated with polyglandular autoimmune (PGA) syndrome, type I, appear to be equivalent to the individual components of the syndrome. Certainly morbidity and mortality can be reduced with improved case findings in relatives of index cases. In individual cases, early detection of life-threatening complications, such as adrenal crisis, hypocalcemia, and sepsis, is prudent.

Race

As discussed in Frequency, ethnic clustering of polyglandular autoimmune (PGA) syndrome, type I, has been observed in certain ethnic populations. Sporadic cases reported around the world have most likely been caused by various isolated mutations, many of which have been identified.

Sex

The female-to-male ratio for polyglandular autoimmune (PGA) syndrome, type I, ranges from 0.8:1 to 1.5:1, as reported in earlier case series. Figures from 2003 indicate that this ratio is between 0.8:1 and 2.4:1, indicating some tendency toward female preponderance.^[11] A sporadic report from Italy, by Iannello and colleagues, showed a rather exclusive female preponderance in an X-linked inheritance fashion.^[12] In reports from around the world, however, autosomal recessive inheritance has been found to be the genetic mode of transmission in most families.

Age

Polyglandular autoimmune (PGA) syndrome, type I, usually occurs in children aged 3-5 years or in early adolescence, but it always occurs by the early part of the third decade of life. A general trend has been noted in the order of appearance of the 3 major systemic manifestations, eg, candidiasis, hypoparathyroidism, and Addison disease. However, that is not always the case, and decades may pass before the appearance of newer syndromic components. Therefore, lifelong follow-up is prudent for early detection of additional components. This cannot be overemphasized, because unrecognized hypoparathyroidism or adrenal insufficiency can be life-threatening.