Novel TMEM67 mutations and genotype-phenotype correlates in meckelin-related ciliopathies.

Human ciliopathies are hereditary conditions caused by defects of proteins expressed at the primary cilium. Among ciliopathies, Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS) and nephronophthisis (NPH) present clinical and genetic overlap, being allelic at several loci. One of the most interesting gene is TMEM67, encoding the transmembrane protein meckelin. We performed mutation analysis of TMEM67 in 341 probands, including 265 JSRD representative of all clinical subgroups and 76 MKS fetuses. We identified 33 distinct mutations, of which 20 were novel, in 8/10 (80%) JS with liver involvement (COACH phenotype) and 12/76 (16%) MKS fetuses. No mutations were found in other JSRD subtypes, confirming the strong association between TMEM67 mutations and liver involvement. Literature review of all published TMEM67 mutated cases was performed to delineate genotype-phenotype correlates. In particular, comparison of the types of mutations and their distribution along the gene in lethal versus non lethal phenotypes showed in MKS patients a significant enrichment of missense mutations falling in TMEM67 exons 8 to 15, especially when in combination with a truncating mutation. These exons encode for a region of unknown function in the extracellular domain of meckelin

Stress-induced unfolded protein response contributes to Zika virus-associated microcephaly.

Accumulating evidence support a causal link between Zika virus (ZIKV) infection during gestation and congenital microcephaly. However, the mechanism of ZIKV-associated microcephaly remains unclear. We combined analyses of ZIKV-infected human fetuses, cultured human neural stem cells and mouse embryos to understand how ZIKV induces microcephaly. We show that ZIKV triggers endoplasmic reticulum stress and unfolded protein response in the cerebral cortex of infected postmortem human fetuses as well as in cultured human neural stem cells. After intracerebral and intraplacental inoculation of ZIKV in mouse embryos, we show that it triggers endoplasmic reticulum stress in embryonic brains in vivo. This perturbs a physiological unfolded protein response within cortical progenitors that controls neurogenesis. Thus, ZIKV-infected progenitors generate fewer projection neurons that eventually settle in the cerebral cortex, whereupon sustained endoplasmic reticulum stress leads to apoptosis. Furthermore, we demonstrate that administration of pharmacological inhibitors of unfolded protein response counteracts these pathophysiological mechanisms and prevents microcephaly in ZIKV-infected mouse embryos. Such defects are specific to ZIKV, as they are not observed upon intraplacental injection of other related flaviviruses in mice

Novel TMEM67 mutations and genotype-phenotype correlates in meckelin-related ciliopathies

Human ciliopathies are hereditary conditions caused by defects of proteins expressed at the primary cilium. Among ciliopathies, Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS) and nephronophthisis (NPH) present clinical and genetic overlap, being allelic at several loci. One of the most interesting gene is TMEM67, encoding the transmembrane protein meckelin. We performed mutation analysis of TMEM67 in 341 probands, including 265 JSRD representative of all clinical subgroups and 76 MKS fetuses. We identified 33 distinct mutations, of which 20 were novel, in 8/10 (80%) JS with liver involvement (COACH phenotype) and 12/76 (16%) MKS fetuses. No mutations were found in other JSRD subtypes, confirming the strong association between TMEM67 mutations and liver involvement. Literature review of all published TMEM67 mutated cases was performed to delineate genotype-phenotype correlates. In particular, comparison of the types of mutations and their distribution along the gene in lethal versus non lethal phenotypes showed in MKS patients a significant enrichment of missense mutations falling in TMEM67 exons 8 to 15, especially when in combination with a truncating mutation. These exons encode for a region of unknown function in the extracellular domain of meckelin