RESUMO
Cohen syndrome is a rare, clinically variable autosomal recessive disorder characterized by mental retardation, postnatal microcephaly, facial dysmorphisms, ocular abnormalities and intermittent neutropenia. Mutations in the COH1 gene have been found in patients from different ethnic origins. However, a high percentage of patients have only one or no mutated allele. To investigate whether COH1 copy number changes account for missed mutations, we used multiplex ligation-dependent probe amplification (MLPA) to test a group of 14 patients with Cohen syndrome. This analysis has allowed us to identify multi-exonic deletions in 11 alleles and duplications in 4 alleles. Considering our previous study, COH1 copy number variations represent 42% of total mutated alleles. To our knowledge, COH1 intragenic duplications have never been reported in Cohen syndrome. The three duplications encompassed exons 4-13, 20-30 and 57-60, respectively. Interestingly, four deletions showed the same exon coverage (exons 6-16) with respect to a deletion recently reported in a large Greek consanguineous family. Haplotype analysis suggested a possible founder effect in the Mediterranean basin. The use of MLPA was therefore crucial in identifying mutated alleles undetected by traditional techniques and in defining the extent of the deletions/duplications. Given the high percentage of identified copy number variations, we suggest that this technique could be used as the initial screening method for molecular diagnosis of Cohen syndrome.
Assuntos
Deleção de Genes , Duplicação Gênica , Proteínas de Transporte Vesicular/genética , Adolescente , Adulto , Sequência de Bases , Criança , Pré-Escolar , Variações do Número de Cópias de DNA , Análise Mutacional de DNA , Deficiências do Desenvolvimento/genética , Dedos/anormalidades , Dosagem de Genes , Genes Recessivos , Haplótipos , Humanos , Lactente , Deficiência Intelectual/genética , Microcefalia/genética , Pessoa de Meia-Idade , Técnicas de Sonda Molecular , Hipotonia Muscular/genética , Miopia/genética , Obesidade/genética , Reação em Cadeia da Polimerase , Degeneração RetinianaRESUMO
BACKGROUND: Coffin-Lowry syndrome is a semi-dominant condition characterized by severe psychomotor retardation with facial, hand and skeletal malformations resulting from mutations in RSK2 gene, encoding for a serine/threonine kinase. More than 100 different mutations have been identified to date; however, about 50% of clinically diagnosed patients apparently do not have mutations. In order to exclude that these patients have RSK2 mutations missed by standard mutation detection techniques, a rapid and sensitive assay allowing evaluation of RSK2 activity was needed. METHODS: RSK2 capacity to phosphorylate a synthetic CREB-peptide in basal and PMA-stimulated conditions was evaluated in lymphoblasts from 3 patients with RSK2 mutations and normal controls. RESULTS: Patients RSK2 activity is normal in nonstimulated conditions but fails to grow following stimulation. The evaluation of the stimulated/non-stimulated activity ratio demonstrated a statistically significant impairment in patients. CONCLUSIONS: We have set up an assay which allows the identification of even partial alterations of RSK2 activity and seems to give good results also in females with a balanced X-chromosome inactivation and thus with a presumably normal enzymatic activity in about 50% of cells. Moreover, our data seem to confirm previous reports of a potential direct correlation between the level of RSK2 activity and the severity of cognitive impairment.
