SummaryGenetic alterations of the FOXN1 transcription factor, selectively expressed in thymic epithelia and skin, are responsible in both mice and humans for the Nude/SCID phenotype. The first described human FOXN1 mutation was a C792T transition in exon 5 resulting in the nonsense mutation R255X, and was detected in two probands originated from a small community in southern Italy. In this community, four additional children affected with congenital alopecia died in early childhood because of severe infections. In this study, we report on the screening for this mutation in 30% of the village population. This analysis led us to identify 55 heterozygous carriers (6.52%) of the R255X mutation out of 843 inhabitants screened. A genealogical study revealed that these subjects, belonging to 39 families, were linked in an extended 7-generational pedigree comprising 483 individuals. Through the archival database a single ancestral couple, born at the beginning of the 19th century, was identified. To confirm the ancestral origin of the mutation we genotyped two microsatellite markers, D17S2187 and D17S1880, flanking the FOXN1 gene on chromosome 17. The three haplotypes identified, 3/R255X/3, 3/R255X/2 and 3/R255X/1, are consistent with a single ancestral origin for the mutation R255X.

Human Nude/SCID (severe combined immunodeficiency) is the first severe combined immunodeficiency caused by mutation of the winged-helix-nude (WHN) gene, which is expressed in the thymus but not in the hematopoietic lineage. The disease is characterized by a T-cell defect, congenital alopecia, and nail dystrophy. A Nude/SCID patient who underwent bone marrow transplantation from the human leukocyte antigen-identical heterozygote brother was studied to investigate, in this unique model, the role of the thymus in immunologic reconstitution. Despite an increase in CD3(+), CD4(+), and CD8(+) cells, CD4(+) CD45 RA naive lymphocytes were not regenerated. Conversely, naive CD8(+) cells were normal. After an initial recovery, lymphocyte proliferation to mitogens progressively declined compared with controls and genotypically identical donor cells grown in the WHN(+/-) environment. Analysis of the T-cell receptor (TCR) repertoire of CD4(+) cells revealed that only 3 of 18 Vbeta families had an altered CDR3 heterogeneity length profile. Conversely, CD8(+) lymphocytes showed an abnormal distribution in most Vbeta families. These data indicate that the thymus is differentially required in the reconstitution of CD4(+) and CD8(+) naive subsets and in the maintenance of their TCR repertoire complexity. Taken together, these findings suggest that bone marrow transplantation is ineffective in the long-term cure of this form of SCID.

SUMMARY Severe combined immunodeficiency (SCID) is a heterogeneous group of disorders characterized by defect of T‐ and B‐cell immunity. In many cases of autosomal recessive SCID, thus far described, the molecular alteration involves genes encoding for molecules that participate in the signal transduction. We report on a patient affected by a combined immunodeficiency, characterized by severe T‐cell functional impairment, in spite of a close to normal number of circulating mature type T and B cells. NK cells were absent. Associated with the immunodeficiency, this patient also showed short stature characterized by very low growth velocity, delayed bone age and absence of increase of the plasma levels of Insulin growth factor‐I (IGF‐I) after growth hormone (GH) in vivo stimulation indicating peripheral hyporesponsiveness to GH. Evaluation of the protein tyrosine phosphorylation events occurring following either T‐cell receptor (TCR) or GH receptor (GHR) triggering revealed striking abnormalities. No molecular alteration of GHR gene was found, thus suggesting the presence of postreceptorial blockage. Mutational screening and expression analysis failed to reveal any molecular alteration of JAK2 and STAT 5 A/B genes thus ruling out the involvement of these genes in the pathogenesis of this form of SCID. Mutational analysis of IL2Rγ chain gene revealed the presence of a L183S missense mutation, thus indicating an atypical and a more complex clinical presentation of this X‐linked form of SCID. At our knowledge, this is the first report on the GH hyporesponsiveness in this disease.

Peripheral GH insensitivity may underlie idiopathic short stature in children. As the clinical and biochemical hallmarks of partial GH insensitivity have not yet been clearly elucidated, the identification of such patients is still difficult. We integrated functional, biochemical, and molecular studies to define the more reliable marker(s) of GH insensitivity. In particular, we measured GH receptor transducing properties through GH-induced protein tyrosine phosphorylation in patients' peripheral blood mononuclear cells and performed direct sequencing analysis of GH receptor-coding exons. Five of 14 idiopathic short stature patients with low basal IGF-I levels showed low or absent IGF-I increment after 4 d of GH administration. However, a prolonged GH stimulation induced in 3 of them an increase in IGF-I 40% above the baseline value. The IGF-binding protein-3 behavior paralleled that of IGF-I. The 2 GH-unresponsive subjects showed an abnormal tyrosine phosphorylation pattern after GH challenge. Sequence analysis of the GH receptor gene revealed a heterozygous mutation resulting in an Arg to Cys change (R161C) in exon 6 in only 1 patient, who had normal GH receptor responsiveness. Our findings indicate that abnormal GH receptor signaling may underlie idiopathic short stature even in the absence of GH receptor mutations. Thus, combining the 4-d IGF-I generation test and the analysis of GH-induced protein tyrosine phosphorylation is a useful tool to help identify idiopathic short stature patients with partial GH insensitivity.