Context: Familial glucocorticoid deficiency (FGD) is an autosomal recessive disorder characterized by distinct clinical, biochemical and genetic abnormalities. The prevalence of FGD is unknown with the likelihood that cases remain undiagnosed. We noted a significant proportion of our FGD cases are Irish Travelers. Irish Travelers are an endogamous nomadic group ethnically and genetically distinct from Roma gypsies.

Aims: To describe the clinical features and assess the prevalence of FGD amongst Irish Travelers in the Republic of Ireland and describe their phenotype.

Methods: Diagnosis of FGD was based on clinical features, high ACTH and low cortisol concentrations with normal renin and aldosterone concentrations and exclusion of other causes of adrenal failure. Data from the Republic of Ireland Census 2006 were used.

Results: We identified 21 cases of FGD generating an overall prevalence of 1 in 201,898. We report 9 Irish Travelers, (5 female) with FGD related to a new gene negative for MC2R and MRAP mutations. Out of a total population of 22,557 Travelers: this yields a disease prevalence of 1 in 2506 with a carrier frequency of 1 in 25 in this group and represents a prevalence of 1 in 665 and a carrier frequency of 1 in 13 in the 4–15year Traveler age group. All 9 children had a later onset of FGD due to the fact that their initial investigations revealed normal cortisol (422–575nmol/L) and ACTH (<34ng/L) concentrations.

Conclusion: We report a high prevalence of FGD amongst Irish Travelers. Their subtle phenotype and initial normal biochemistry may delay the early diagnosis of FGD.