The discovery that mutations in the human nuclear receptor gene DAX1
give rise to both X-linked AHC and HHG (1
) has provided new insight into the pathogenesis of this syndrome. Here, we report the remarkable case of a man with a novel missense mutation in DAX1
who presented with late-onset adrenal insufficiency, incomplete HHG, and severe oligospermia that was unresponsive to gonadotropin therapy. This case extends the clinical phenotype of DAX1
mutations to include patients with a milder disorder and delayed onset of symptoms.
The presentation of adrenal failure at 28 years of age in this patient contrasts markedly with classic cases of AHC. Boys with this condition typically develop acute adrenocortical failure shortly after birth or during early childhood, with a median age at presentation of 3 weeks (9
). Rare cases of delayed onset adrenal failure (26
), or progressive deterioration of adrenal function after an asymptomatic period during infancy have been described (31
). However, in all other cases reported to date, unequivocal symptoms of adrenal failure appeared before the age of 10 years (13
). The clinical picture described here, including the slow progression of symptoms in adulthood, absence of family history, and subclinical and undiagnosed HHG, might otherwise point to a diagnosis of autoimmune adrenal failure. Mutations in DAX1
should now be considered in the differential diagnosis of such patients.
Although the pituitary-gonadal axis may be intact in early infancy in boys with AHC (32
), failure to undergo puberty due to hypogonadotropic hypogonadism is a hallmark of this condition (9
). Recently, spontaneous onset of puberty has been described in 3 boys with DAX1
). Nevertheless, gonadotropin deficiency developed rapidly between 15 and 18 years in these individuals, resulting in failure of further pubertal development and low testosterone concentrations (35
). The patient presented here demonstrates that DAX1
mutations may result in even milder forms of HHG. Serum testosterone concentrations were sufficient to allow significant masculinization to occur at the time of puberty, and from the patient’s point of view, an acceptable level of sexual activity during adulthood.
It remains debatable whether HHG associated with DAX1
mutations results from hypothalamic or pituitary dysfunction (9
). DAX-1 is expressed at both these levels (2
), and recent studies suggest that they may both be involved (29
). Our patient’s response to pulsatile GnRH administration was less than might be expected for someone with a selective hypothalamic GnRH deficiency (e.g., Kallmann syndrome) (20
), suggesting at least a partial pituitary component to the defect in gonadotropin production. However, most of our results favor a predominant hypothalamic defect in this case, including: (a) the normalization of serum testosterone concentration after pulsatile administration of GnRH for 5 days; (b) the dramatic and sustained increase of FSH, LH, FAS, and testosterone after administration of a GnRH agonist analogue (36
); (c) the erratic and asynchronous pattern of pulsatile LH and FAS secretion, which is assumed to reflect the activity of GnRH-secreting hypothalamic neurons (20
); and (d) the low serum LH/FSH ratio (20
Although HHG in this patient was incomplete, he had severe oligospermia, raising the possibility that DAX-1 may affect spermatogenesis directly. DAX-1 is known to be expressed in Sertoli cells in rats (39
), and targeted disruption of Ahch
) in mice results in infertility despite apparently normal gonadotropin and adrenal steroid production (10
). Indeed, progressive epithelial dysgenesis and loss of germ cells is seen after birth in these animals, consistent with a primary Sertoli cell defect (10
). Exogenous gonadotropin therapy did not correct the oligospermia in this patient, indicating that the impaired spermatogenesis results from mechanisms other than HHG. In addition, the low serum inhibin B concentration, despite a slightly elevated serum immunoreactive FSH concentration (41
), provides further evidence that DAX-1 mutations cause primary defects in Sertoli cell function (10
). Taken together, these data suggest that abnormalities of spermatogenesis may also comprise part of the clinical spectrum of AHC.
The coexpression of DAX-1 with SF-1 in the gonadal and adrenal axes (2
), and the adrenal failure seen in patients with mutations in these genes (11
), suggest that DAX-1 and SF-1 interact in a common genetic pathway. An SF-1 response element has been identified in the DAX1
), and SF-1 activates Ahch
) expression (8
), while in vitro studies have consistently shown that DAX-1 actually represses
SF-1–mediated transactivation. Indeed, DAX-1 also inhibits transcription of SF-1 target genes involved in adrenal steroidogenesis, such as steroidogenic acute regulatory protein (StAR
, and 3β-hydroxysteroid dehydrogenase (43
). This repression is compatible with the XY sex reversal seen in association with overexpression of Ahch/Dax1
in mice (45
) and humans (46
), where DAX-1 is thought to antagonize the actions of the testis-determination factor, SRY, in gonadal development. However, a repressor role for DAX-1 in the adrenal and reproductive axes is more difficult to understand. Nevertheless, functional studies have shown that the transcriptional silencing activity of the DAX-1 protein is localized to the carboxy terminus, corresponding to the putative LBD (6
Diseases caused by natural mutations provide insight into the relationship between the structure and function of the proteins encoded by the mutant genes. Remarkably, all mutations associated with AHC reported to date alter the structure of the carboxy terminus of the DAX-1 protein (1
). The majority of these are frameshift or nonsense (stop codon) mutations that result in a truncated protein. There is no obvious correlation between the putative structural consequences of these mutations and the clinical phenotype (13
). Indeed, the age at onset of adrenal insufficiency can vary within the same family, suggesting that other epigenetic or nongenetic factors influence the clinical course of AHC (11
). Analysis of phenotypes associated with missense mutations that result in single amino acid substitutions might be more helpful in revealing the relationships with genotypes and identifying important functional domains in the DAX-1 protein. About 10 different missense mutations in DAX-1 have been reported to date (11
). These are all located within the putative LBD of DAX-1, as is the novel I439S mutant described here (Figure a). The I439S mutation appears to represent an example of a DAX-1 mutation associated with a mild phenotype.
Functional studies were undertaken, therefore, to assess the effects of the mutant I439S DAX-1 protein on transcriptional repression. The naturally occurring DAX-1 mutations, R267P and ΔV269, and a deletion mutant, Δ448–470, were included as positive controls because these are associated with clinically severe phenotypes and have been shown to reduce the inhibitory activity of DAX-1 in transient gene expression assays (5
). As expected, wild-type DAX-1 exerted strong repression of basal transcriptional activity (6
), SF-1 mediated transcriptional activation (5
), and SF-1/Egr-1 synergistic activation of the LHβ gene promoter (25; LHβ
is a natural DAX-1 target gene). A significant reduction in repressor activity was seen with the R267P, ΔV269, and Δ448–470 mutants, whereas the I439S mutant had less effect on DAX-1 repressor activity. The partial loss of function seen with the I439S mutant is consistent with the mild clinical phenotype described in the patient. In addition, these data provide the first evidence that naturally occurring DAX-1 mutations affect the ability of DAX-1 to repress LHβ
, a natural target gene in the reproductive axis.
In conclusion, this case extends the spectrum of X-linked AHC to include delayed onset of adrenocortical insufficiency in adulthood and subclinical HHG. The diagnosis of AHC should be considered in men with apparent idiopathic Addison’s disease. After steroid replacement, careful assessment of the reproductive axis and gonadal function should be undertaken, and mutational analysis of DAX1 should be considered. Similarly, DAX1 should be considered a candidate gene in young adults presenting with mild “idiopathic” HHG. Additional studies of the spermatogenic response to gonadotropin therapy are required to confirm the probable AHC-associated infertility in these patients.