PTEN mutations as a cause of constitutive insulin sensitivity and obesity.

BACKGROUND: Epidemiologic and genetic evidence links type 2 diabetes, obesity, and cancer. The tumor-suppressor phosphatase and tensin homologue (PTEN) has roles in both cellular growth and metabolic signaling. Germline PTEN mutations cause a cancer-predisposition syndrome, providing an opportunity to study the effect of PTEN haploinsufficiency in humans. METHODS: We measured insulin sensitivity and beta-cell function in 15 PTEN mutation carriers and 15 matched controls. Insulin signaling was measured in muscle and adipose-tissue biopsy specimens from 5 mutation carriers and 5 well-matched controls. We also assessed the effect of PTEN haploinsufficiency on obesity by comparing anthropometric indexes between the 15 patients and 2097 controls from a population-based study of healthy adults. Body composition was evaluated by means of dual-emission x-ray absorptiometry and skinfold thickness. RESULTS: Measures of insulin resistance were lower in the patients with a PTEN mutation than in controls (e.g., mean fasting plasma insulin level, 29 pmol per liter [range, 9 to 99] vs. 74 pmol per liter [range, 22 to 185]; P=0.001). This finding was confirmed with the use of hyperinsulinemic euglycemic clamping, showing a glucose infusion rate among carriers 2 times that among controls (P=0.009). The patients' insulin sensitivity could be explained by the presence of enhanced insulin signaling through the PI3K-AKT pathway, as evidenced by increased AKT phosphorylation. The PTEN mutation carriers were obese as compared with population-based controls (mean body-mass index [the weight in kilograms divided by the square of the height in meters], 32 [range, 23 to 42] vs. 26 [range, 15 to 48]; P<0.001). This increased body mass in the patients was due to augmented adiposity without corresponding changes in fat distribution. CONCLUSIONS: PTEN haploinsufficiency is a monogenic cause of profound constitutive insulin sensitization that is apparently obesogenic. We demonstrate an apparently divergent effect of PTEN mutations: increased risks of obesity and cancer but a decreased risk of type 2 diabetes owing to enhanced insulin sensitivity. (Funded by the Wellcome Trust and others.).

Ulnar Mammary syndrome and TBX3: expanding the phenotype.

We present a patient with features of Ulnar Mammary syndrome (UMS) consisting of bilateral ulnar defects, inverted nipples, short stature with associated growth hormone deficiency, and cryptorchidism. Our patient also had a hypoplastic anterior pituitary and an ectopic posterior pituitary gland, ventricular septal defect (VSD), and cardiac conduction defects consistent with Wolff-Parkinson-White (WPW) syndrome. Although TBX3 is known to be expressed in both the developing heart and the pituitary gland, conduction defects and anatomical pituitary abnormalities have not been previously described in UMS. This may, in part, be due to the fact that these features are not actively sought in individuals with UMS. Because these new findings have important clinical implications, we suggest that clinicians caring for individuals with UMS offer brain imaging, growth hormone testing, and cardiac arrhythmia screening. The diagnosis of UMS was confirmed on mutation analysis of TBX3. The mother of the propositus was also found to carry the same mutation, although she did not show the classical features of UMS. Therefore, our report also supports the variable expressivity of UMS within the same family.