RESUMO
Mutations in the gene encoding the neural cell adhesion molecule L1CAM cause several neurological disorders collectively referred to as L1 syndrome. We report here a family case of X-linked hydrocephalus in which an obligate female carrier has two exonic L1CAM missense mutations in trans substituting amino acids in the first (p.W635C) or second (p.V768I) fibronectin-type III domains. We performed various biochemical and cell biological in vitro assays to evaluate the pathogenicity of these variants. Mutant L1-W635C protein accumulates in the endoplasmic reticulum (ER), is not transported into axons, and fails to promote L1CAM-mediated cell-cell adhesion as well as neurite growth. Immunoprecipitation experiments show that L1-W635C associates with the molecular ER chaperone calnexin and is modified by poly-ubiquitination. The mutant L1-V768I protein localizes at the cell surface, is not retained in the ER, and promotes neurite growth similar to wild-type L1CAM. However, the p.V768I mutation impairs L1CAM-mediated cell-cell adhesion albeit less severe than L1-W635C. These data indicate that p.W635C is a novel loss-of-function L1 syndrome mutation. The p.V768I mutation may represent a non-pathogenic variant or a variant associated with low penetrance. The poly-ubiquitination of L1-W635C and its association with the ER chaperone calnexin provide further insights into the molecular mechanisms underlying defective cell surface trafficking of L1CAM in L1 syndrome.
Assuntos
Éxons , Doenças Genéticas Ligadas ao Cromossomo X/genética , Variação Genética , Hidrocefalia/genética , Molécula L1 de Adesão de Célula Nervosa/genética , Adulto , Linhagem Celular , Aqueduto do Mesencéfalo/anormalidades , Aqueduto do Mesencéfalo/metabolismo , Aqueduto do Mesencéfalo/patologia , Análise Mutacional de DNA , Feminino , Doenças Genéticas Ligadas ao Cromossomo X/metabolismo , Doenças Genéticas Ligadas ao Cromossomo X/patologia , Humanos , Hidrocefalia/metabolismo , Hidrocefalia/patologia , Masculino , Pessoa de Meia-Idade , Mutação , Neurônios/citologia , Neurônios/fisiologia , LinhagemRESUMO
OBJECTIVE: To study pericentric inversion segregation and interchromosomal effect on sperm for men heterozygous for inv(2)(p11q13), to assess the risk of miscarriage. DESIGN: Case report. SETTING: Department of reproductive biology, cytogenetics, gynecology, and obstetrics. PATIENT(S): Seven patients heterozygous for inv(2)(p11q13) and five patients with normal karyotype with experience of recurrent spontaneous miscarriage. INTERVENTION(S): Fluorescence in situ hybridization on sperm with 2 p and 2q subtelomeric probes to screen for inversion segregation, and X, Y, and 18 centromeric probes to study interchromosomal effects. One thousand sperm were analyzed per experiment and per patient. MAIN OUTCOME MEASURE(S): Rate of unbalanced chromosomes and aneuploid sperm. RESULT(S): The inv(2)(p11q13) patients showed a 0.3% rate of sperm with unbalanced chromosomes. For interchromosomal effects, a 0.6% aneuploid sperm rate was observed for patients heterozygous for inv(2)(p11q13). This is similar to the 0.5% rate observed for control patients. CONCLUSION(S): Inv(2)(p11q13) seems not to increase miscarriage for couples with men heterozygous for this inversion.