The ciliopathy Joubert syndrome is marked by cerebellar vermis hypoplasia, a phenotype for which the pathogenic mechanism is unclear1–3. In order to investigate Joubert syndrome pathogenesis, we have examined mice with mutated Ahi1, the first identified Joubert syndrome gene4,5. These mice exhibit cerebellar hypoplasia with a vermis/midline fusion defect early in development. This defect is concomitant with expansion of the roof plate and is also evident in a mouse mutant for another Joubert syndrome gene, Cep2906,7. Further, fetal magnetic resonance imaging (MRI) from human subjects with Joubert syndrome reveals a similar midline cleft suggesting parallel pathogenic mechanisms. Previous evidence has suggested a role for Jouberin (Jbn), the protein encoded by Ahi1, in canonical Wnt signaling8. Consistent with this, we found decreased Wnt reporter activity at the site of hemisphere fusion in the developing cerebellum of Ahi1 mutant mice. This decrease was accompanied by reduced proliferation at the site of fusion. Finally, treatment with lithium, a Wnt pathway agonist9, partially rescued this phenotype. Our findings implicate a defect in Wnt signaling in the cerebellar midline phenotype seen in Joubert syndrome, which can be overcome with Wnt stimulation.

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MRI of the fetal heart with a steady-state free precession sequence in multiple planes and image analysis with an anatomic segmental approach to congenital heart disease are possible in situations that limit echocardiography.

Fetal MRI is an important adjunct to US in assessing NTD. It can identify topography and contents of sacs, add CNS and non-CNS findings, and influence management decision.

The hypothalamus is susceptible to involvement by a variety of processes, including developmental abnormalities, primary tumors of the central nervous system (CNS), vascular tumors, systemic tumors affecting the CNS, and inflammatory and granulomatous diseases. The hypothalamus may also be involved by lesions arising from surrounding structures such as the pituitary gland. Magnetic resonance (MR) imaging is the modality of choice for evaluating the anatomy and pathologic conditions of the hypothalamus. The MR imaging differential diagnosis depends on accurate anatomic localization and tissue characterization of hypothalamic lesions through the recognition of their signal intensity and contrast material enhancement patterns. Diffusion-weighted imaging and proton MR spectroscopy can be helpful in differentiating among various types of hypothalamic lesions. Key MR imaging features, in addition to the patient's age and clinical findings at presentation, may be helpful in developing the differential diagnosis for lesions involving the hypothalamic region.