A neuropatia auditiva consiste no acometimento do nervo auditivo, que gera uma dessincronia na condução nervosa, provavelmente relacionada com alterações de mielinização dessas fibras. Clinicamente, há uma perda auditiva e alteração na discriminação vocal. As otoemissões acústicas se apresentam normais com BERA não responsivo. Pode haver correlação com algumas patologias que cursam com neuropatia periférica. Os autores fazem uma revisão da literatura e relatam um caso de uma paciente portadora de neuropatia auditiva associada à retinose pigmentar com discussão das possíveis etiologias.
Mauro
Mitochondrial mutations are responsible for at least 1% of the cases of hereditary deafness, but the contribution of each mutation has not yet been defined in African-derived or native American genetic backgrounds. A total of 203 unselected hearing-impaired patients were screened for the presence of the mitochondrial mutation A1555G in the 12S rRNA gene and mutations in the tRNA Ser(UCN) gene in order to assess their frequency in the ethnically admixed Brazilian population. We found four individuals with A1555G mutation (2%), which is a frequency similar to those reported for European-derived populations in unselected samples. On the other hand, complete sequencing of the tRNA Ser(UCN) did not reveal reported pathogenic substitutions, namely A7445G, 7472insC, T7510C, or T7511C. Instead, other rare substitutions were found such as T1291C, A7569G, and G7444A. To evaluate the significance of these findings, 110 "European-Brazilians" and 190 "African-Brazilians" unrelated hearing controls were screened. The T1291C, A7569G and G7444A substitutions were each found in about 1% (2/190) of individuals of African ancestry, suggesting that they are probably polymorphic. Our results indicate that screening for the A1555G mutation is recommended among all Brazilian deaf patients, while testing for mutations in the tRNA Ser(UCN) gene should be considered only when other frequent deafness-causing mutations have been excluded or in the presence of a maternal transmission pattern.
Speech/language disorders are common in the fragile X syndrome. [Howard-Peebles, 1979: Am J Hom Genet 31:214-222; Renier et al., 1983: J Ment Defic Res 27:51-59; Sparks, 1984: Birth Defects and Speech-Language Disorders, pp. 39-43; Hanson et al., 1986: Am J Med Genet 23:195-206]. Verbal paraphasias have been considered a rare feature and word-finding difficulties have seldom been reported. Here we report on ten Brazilian patients who were evaluated for speech/language disturbances and found that word-finding difficulties were present in 50% of the cases, which is a slightly higher frequency than that of clear dyspraxia. We suggest, therefore, that word-finding difficulties and verbal dyspraxia can be a common feature within the spectrum of this syndrome. Additional speech findings are discussed.
Hearing impairment is frequently found associated with pigmentary disorders in many syndromes. However, total oculocutaneous albinism (OCA) associated with deafness has been described only once, by Ziprkowski and Adam (Arch Dermatol 89:151-155, 1964) in an inbred family. A syndrome associating deafness and OCA was suggested by the authors, but two separate recessive genes segregating in this inbred group were also proposed later by Fraser (OMIM # 220900). Combined deafness and total OCA were also observed by us in a family originally reported to be nonconsanguineous but in which haplotyping showed evidence of a common ancestry: the proband was affected by both diseases, one of his sisters had only OCA and another sister had only deafness. Both the proband and his deaf sister were found to be homozygotes for the 35delG mutation (GJB2 gene), the most frequent cause of hereditary deafness. Linkage analysis with markers close to the four known OCA loci excluded linkage to OCA1, OCA2, and OCA3, and homozygosity in markers near OCA4 locus was observed. Sequencing of the corresponding gene (MATP) revealed a c.1121delT mutation, which leads to a stop codon at position 397 (L374fsX397). Clearly, the combined occurrence of deafness and albinism in this pedigree was due to mutations in two different genes, showing autosomal recessive inheritance. We speculate that the putative syndrome reported by Ziprkowski and Adam might have resulted from the co-occurrence of autosomal recessive deafness and albinism in the same pedigree, as suggested by Fraser.
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