Six year old with autoimmune polyglandular syndrome: can genetics tell us the story?

Children who have diabetes mellitus type 1 (DMT1) are at increased risk of developing other autoimmune diseases. These associated diseases include Hashimoto's thyroiditis, Graves' disease, Celiac disease, and Addison's disease. Since Addison's disease is potentially fatal if undiagnosed and untreated, it would be prudent to effectively screen individuals to determine if they are at risk of developing this disease. We present a case of a 6 year old male with a history of DMT1, who presented in adrenal crisis and was subsequently diagnosed with Addison's disease. HLA-DRB1 404/DR4 is one of the genes involved in the development of Addison's disease in children with DMT1. Our patient later tested positive for this haplotype. Genetic testing is not routinely done in patients with (DMT1) to determine if they will potentially develop other associated conditions. We propose using genetic testing of associated HLA haplotypes to screen children with DMT1 for Addison's disease.

Atypical GH insensitivity syndrome and severe insulin-like growth factor-I deficiency resulting from compound heterozygous mutations of the GH receptor, including a novel frameshift mutation affecting the intracellular domain.

BACKGROUND/AIMS: GH insensitivity and IGF deficiency may result from aberrations of the GH receptor (GHR). We describe a 4-year-old child with modest growth failure and normal serum concentrations of GH-binding protein (GHBP), but clinical evidence of GH insensitivity. METHOD: Serum and DNA samples from the proband and his parents were analyzed. RESULTS: The child had a height of -4 SD, elevated serum GH concentrations, abnormally low serum IGF-I and IGFBP-3 concentrations and normal GHBP concentrations. DNA analysis revealed compound heterozygosity for mutations of GHR, including a previously reported R211H mutation and a novel duplication of a nucleotide in exon 9 (899dupC), the latter resulting in a frameshift and a premature stop codon. Treatment with recombinant DNA-derived IGF-I resulted in growth acceleration. CONCLUSION: Mutations affecting the intracellular domain of the GHR can result in GH insensitivity and IGF deficiency, despite normal serum concentrations of GHBP. The presence of clinical and biochemical evidence of GH resistance is sufficient to consider the possibility of aberrations of the GHR, even in the presence of normal serum GHBP concentrations.

Leucine restriction inhibits chondrocyte proliferation and differentiation through mechanisms both dependent and independent of mTOR signaling.

Linear growth in children is sensitive to nutritional status. Amino acids, in particular leucine, have been shown to regulate cell growth, proliferation, and differentiation through the mammalian target of rapamycin (mTOR), a nutrient-sensing protein kinase. Having recently demonstrated a role for mTOR in chondrogenesis, we hypothesized that leucine restriction, acting through mTOR, would inhibit growth plate chondrocyte proliferation and differentiation. The effect of leucine restriction was compared with that of the specific mTOR inhibitor, rapamycin. Leucine restriction produced a dose-dependent inhibition of fetal rat metatarsal explant growth. This was accounted by reduced cell proliferation and hypertrophy but not apoptosis. mTOR activity, as reflected by ribosomal protein S6 phosphorylation, was only partially inhibited by leucine restriction, whereas rapamycin abolished S6 phosphorylation. In chondrogenic ATDC5 cells, leucine restriction inhibited cell number, proteoglycan accumulation, and collagen X expression despite minimal inhibition of mTOR. Microarray analysis demonstrated that the effect of leucine restriction on ATDC5 cell gene expression differed from that of rapamycin. Out of 1,571 genes affected by leucine restriction and 535 genes affected by rapamycin, only 176 genes were affected by both. These findings indicate that the decreased chondrocyte growth and differentiation associated with leucine restriction is only partly attributable to inhibition of mTOR signaling. Thus nutrient restriction appears to directly modulate bone growth through unidentified mTOR-independent mechanisms in addition to the well-characterized mTOR nutrient-sensing pathway.

mTOR signaling contributes to chondrocyte differentiation.

The mammalian Target Of Rapamycin (mTOR) is a nutrient-sensing protein kinase that regulates numerous cellular processes. Fetal rat metatarsal explants were used as a physiological model to study the effect of mTOR inhibition on chondrogenesis. Insulin significantly enhanced their growth. Rapamycin significantly diminished this response to insulin through a selective effect on the hypertrophic zone. Cell proliferation (bromodeoxyuridine incorporation) was unaffected by rapamycin. Similar observations were made when rapamycin was injected to embryonic day (E) 19 fetal rats in situ. In the ATDC5 chondrogenic cell line, rapamycin inhibited proteoglycan accumulation and collagen X expression. Rapamycin decreased content of Indian Hedgehog (Ihh), a regulator of chondrocyte differentiation. Addition of Ihh to culture medium reversed the effect of rapamycin. We conclude that modulation of mTOR signaling contributes to chondrocyte differentiation, perhaps through its ability to regulate Ihh. Our findings support the hypothesis that nutrients, acting through mTOR, directly influence chondrocyte differentiation and long bone growth.