Various mechanisms cause RET-mediated signaling defects in Hirschsprung's disease.

Hirschsprung's disease (HSCR) is a common congenital malformation characterized by the absence of intramural ganglion cells of the hindgut. Recently, mutations of the RET tyrosine kinase receptor have been identified in 50 and 15-20% of familial and sporadic HSCR, respectively. These mutations include deletion, insertion, frameshift, nonsense, and missense mutations dispersed throughout the RET coding sequence. To investigate their effects on RET function, seven HSCR missense mutations were introduced into either a 1114-amino acid wild-type RET isoform (RET51) or a constitutively activated form of RET51 (RET-MEN 2A). Here, we report that one mutation affecting the extracytoplasmic cadherin domain (R231H) and two mutations located in the tyrosine kinase domain (K907E, E921K) impaired the biological activity of RET-MEN 2A when tested in Rat1 fibroblasts and pheochromocytoma PC12 cells. However, the mechanisms resulting in RET inactivation differed since the receptor bearing R231H extracellular mutation resulted in an absent RET protein at the cell surface while the E921K mutation located within the catalytic domain abolished its enzymatic activity. In contrast, three mutations mapping into the intracytoplasmic domain neither modified the transforming capacity of RET-MEN 2A nor stimulated the catalytic activity of RET in our ligand-independent system (S767R, P1039L, M1064T). Finally, the C609W HSCR mutation exerts a dual effect on RET since it leads to a decrease of the receptor at the cell surface and converted RET51 into a constitutively activated kinase due to the formation of disulfide-linked homodimers. Taken together, our data show that allelic heterogeneity at the RET locus in HSCR is associated with various molecular mechanisms responsible for RET dysfunction.

Persistence of nuchal edema and distended jugular lymphatic sacs in Noonan syndrome.

OBJECTIVE: Noonan syndrome is one of the most common genetic syndromes manifesting at birth. Still, it is diagnosed late, often during infancy. Diagnosis is difficult because prenatal ultrasound findings are unspecific and the dysmorphias after birth can be subtle. CASES: Two women were referred to our university hospital because of an increased nuchal translucency in the first trimester of pregnancy. Further ultrasound examination showed the bilateral presence of distended jugular lymph sacs. Karyotyping revealed euploidy in both fetuses. The second trimester ultrasound scan showed a persistence of the jugular lymph sacs together with a nuchal fold, indicating a disturbed lymphatic development. There were no other anomalies. In 1 case the jugular lymph sacs containing newly formed lymph node tissue remained visible until 35 weeks' gestation. Both newborns were diagnosed with Noonan syndrome after birth. Postnatal echocardiography revealed a mild pulmonary stenosis. CONCLUSION: Distension of the jugular lymph sacs is known to cause nuchal edema and normally resolves after the first trimester. In case of persistence of the jugular lymphatic sacs beyond the second trimester of pregnancy, the diagnosis of Noonan syndrome and subsequent DNA testing should be considered.

[Echo-guided percutaneous alcohol injections of cold non-neoplastic thyroid nodules. Preliminary experience]. / Alcolizzazione percutanea ecoguidata dei noduli tiroidei freddi non neoplastici. Esperienza preliminare.

Percutaneous ethanol injection (PEI) has been recently used with excellent results to treat toxic and pretoxic thyroid adenomas. We investigated PEI efficacy also in the treatment of "cold" thyroid nodules in 31 patients with nodular goiter. All nodules were proved to be cold on thyroid scintigraphy. There was no clinical or cytologic suspicion of cancer. Informed consent to the experimental study was always obtained. Each patient received 24 +/- 4.1 ml of ethanol, injected once or twice a week. No significant side-effects were observed during treatment. All nodules shrank 66-97.6% (mean: 85.5%, p < 0.001 vs pretreatment volume). US-guided cytologic sampling was repeated at 3 months' follow-up. PEI was precautionally repeated in 4 patients exhibiting sparse follicular cells. Further data about this group are not available yet. These preliminary results prove PEI to be an effective and safe technique to treat thyroid nodules and to make a valuable alternative to surgery and L-thyroxine.