Identification of three novel mutations in the MYO7A gene

Three new mutations in the myosin VIIA gene involved in the pathogenesis of Usher syndrome type Ib are reported. These mutations are K1080X in exon 25, E1170K in exon 28, and Y1719C in exon 37. It is presumed that these mutations are involved in the Usher syndrome Ib phenotype.

Identification of three novel mutations in the MYO7A gene

Three new mutations in the myosin VIIA gene involved in the pathogenesis of Usher syndrome type Ib are reported. These mutations are K1080X in exon 25, E1170K in exon 28, and Y1719C in exon 37. It is presumed that these mutations are involved in the Usher syndrome Ib phenotype. Hum Mutat 14:181, 1999. Copyright 1999 Wiley-Liss, Inc.

Specific staining of nonpyramidal cell populations of the cerebral cortex by lectin cytochemistry on semithin sections

The pattern of lectin labeling in the cerebral cortex of the cat was studied using semithin sections. The labeling produced by some lectins (Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, wheat germ agglutinin, and succynilated-wheat germ) appeared inside every neuron as small cytoplasmic granules, probably corresponding to cisterns of endoplasmic reticulum and/or the Golgi complex. Lectins with affinity for alpha-mannosyl residues (Pisum sativum, Lens culinaris, and Concanavalin A) stained the cell surface of a subset of cortical neurons. The labeled cells were round or polygonal, medium to large neurons present in layers II-VI, exhibiting the morphological features of nonpyramidal cells. Previous lectin studies of perineuronal nets have shown that these extracellular specializations contain N-acetylgalactosamine and N-acetylglucosamine. Our results show that mannose is also a component of perineuronal nets and that lectins specific for alpha-mannose can be used as tools for the cytochemical detection of a separate class of cortical neurons, which have not yet been fully characterized. In addition, some lectins (Bandeiraea simplicifolia, Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, and succynilated-wheat germ agglutinin) specifically labeled a population of a type of microglia-related cells known as perivascular cells. The data presented here report for the first time the selective staining of perivascular cells and further support the hypothesis that they are different from typical microglial cells.

[Syndromic hereditary deafness. Usher's syndrome. Oto-neurologic and genetic factors]

Usher syndrome (USH) is an autosomal recessive hereditary disorder characterized by congenital bilateral sensorineural hearing loss and progressive loss of vision due to retinitis pigmentosa (RP). The prevalence of Usher syndrome is estimated to be 3-4.4 cases per 100.000 people. Several clinical types have been distinguished by age at onset, rate of progression, and severity of symptoms. Type I (USH1) is characterized by a congenital, severe-to-profound deafness and absent vestibular function. Type II (USH2) shows a congenital and moderate-to-severe hearing loss and normal vestibular response. It is also suggested a third type (USH3), clinically similar to USH2, but with progressive hearing loss. Genetic heterogeneity of USH is quite extensive. Up to now, seven different loci responsible for the defect are known: 14q, 11q, 11p, 10q and 21q for USH1; 1q for USH2 and 3q for USH3. Moreover, there are USH1 and USH2 families that fail to show linkage to these candidate regions demonstrating that should exist other loci causing USH, although their ubications are unknown. To date, only two genes involved in the USH pathology are known, although together they are responsibles of about the 80% of total USH cases: myosin VIIA, an unconventional myosin, involved in the USH1b phenotype and a protein similar to the laminina, responsible for the USH2a phenotype.

Detection of a novel Cys628STOP mutation of the myosin VIIA gene in Usher syndrome type Ib

A Spanish family with three Usher I syndrome-affected members was linked to markers located on chromosome 11q. A search for mutations on the myosin VIIA gene revealed a novel mutation (Cys628STOP) on exon 16 segregating with the disorder in a homozygous state. This nonsense mutation could be responsible for the disease since it leads to a truncated protein that presumably has no function.

Auditory connections and neurochemistry of the sagulum

We studied the cytoarchitecture, neurochemical organization, and connections of the sagulum. The goal was to clarify its role in midbrain, lateral tegmental, and thalamic auditory processing. On cytoarchitectonic grounds, ventrolateral (parvocellular) and dorsomedial (magnocellular) subdivisions were recognized. The patterns of immunostaining for gamma-aminobutyric acid (GABA) and glycine were distinct. Approximately 5-10% of the neurons were GABAergic, and more than one type was identified; GABAergic axon terminals were abundant in number and varied in form. Glycinergic neurons were much rarer, < 1% of the population, and glycinergic axon terminals were correspondingly sparse. Wheat germ agglutinin conjugated to horseradish peroxidase was used for purposes of connectional mapping, and biotinylated dextran amines revealed the structure of corticosagular axons. All nine cortical areas injected project to the ipsilateral sagulum. Five (areas AI, AII, SF, EPD, and Te) had heavier projections than the others. Areas AI and AII projected throughout the rostrocaudal sagulum. Labeling from AI was moderate in density and concentrated in the central sagulum, whereas the input from AII was heavier and ended more laterally. Suprasylvian fringe input was light, especially caudally, and was chiefly in the central sagulum. The projection from the dorsal region of the posterior ectosylvian gyrus was comparatively stronger and was in the dorsolateral sagulum. Finally, the temporal cortex sent axons to the most lateral sagulum, spanning the dorsoventral extent, whereas insular cortex axons ended diffusely in the dorsolateral sagulum. Corticofugal axons ranged from fine boutons en passant to larger globular terminals. The sagulum may represent the earliest significant opportunity in the ascending auditory pathway for corticofugal modulation. The most extensive input arises from the polymodal association areas. The sagulum then projects divergently to the dorsal cortex of the inferior colliculus and the dorsal division of the medial geniculate body. The projection from the dorsal division of the auditory thalamus to nonprimary auditory cortex completes this circuit between the forebrain and the midbrain and represents a nexus in the ascending and descending auditory systems. Such circuits could play a critical role in auditory-motor adjustments to sound.

Ala397Asp mutation of myosin VIIA gene segregating in a Spanish family with type-Ib Usher syndrome

In the current study, 12 Spanish families affected by type-I Usher syndrome, that was previously linked to chromosome 11q, were screened for the presence of mutations in the N-terminal coding portion of the motor domain of the myosin VIIA gene by single-strand conformation polymorphism analysis of the first 14 exons. A mutation (Ala397Asp) segregating with the disease was identified, and several polymorphisms were also detected. It is presumed that the other USHIB mutations in these families could be located in the unscreened regions of the gene.

Linkage analysis in Usher syndrome type I (USH1) families from Spain

Usher syndrome (USH) is an autosomal recessive hereditary disorder characterised by congenital sensorineural hearing loss and gradual visual impairment secondary to retinitis pigmentosa (RP). The disorder is clinically and genetically heterogeneous. With regard to Usher type I (USH1), several subtypes have been described, the most frequent being USH1B located on chromosome 11q13.5. Of 18 USH1 families studied by linkage analysis, 12 (67%) showed significant lod score values for locus D11S527 (Zmax=14.032, theta=0.000) situated on chromosome 11q. Our findings suggest considerable genetic heterogeneity in the Spanish USH1 population. It is important to note that one of our families linked to the USH1B locus shows interesting intrafamilial clinical variability. As regards the remaining six USH1 families, the linkage analysis did not provide conclusive data, although two of them show slight linkage to markers located on chromosome 3q (Zmax=1.880, theta=0.000 for D3S1279), the same location that had previously been assigned to some USH3 families.

Structure of glycogen particles in organ of Corti's outer hair cells in three rodent species

Organ of Corti's outer hair cells are one of the few cell types in mammals to contain large cytoplasmic glycogen stores, and the only one in the adult auditory receptor. Previous reports on the structure and distribution of glycogen in the adult organ of Corti were mainly based on light microscopy histo- and cytochemical methods, and the scare EM studies on the topic relied on techniques which were not sensitive or specific enough. Furthermore, it has been reported that glycogen particles are not present in outer hair cells of all species. A first goal of the present study was to describe the ultrastructure of glycogen stores in organ of Corti's outer hair cells in Guinea pig, rat, and mouse, using the periodic acid-thiocarbohydrazide-silver proteinate method. In addition, differences in the subcellular and cochleotopic distribution of this substance were analyzed. In the adult organ of Corti only the outer hair cells contain glycogen stores. Present throughout their cytoplasm, these deposits appear either as single beta particles, or as aggregates of these, forming alpha particles. Though most alpha particles are round, some appear long and conspicuously straight in longitudinal sections of those cells near the apex of the cochlea, and they seem to be apposed to some filamentous structure. On the other hand, when the cells are sectioned transversely the larger aggregates of glycogen particles follow a curved course. Since outer hair cells of the apical region of the cochlea contain a bundle of contractile microfilaments, our results suggest that glycogen is associated with the contractile apparatus of these cells. This hypothesis is in good accordance with previous experimental data which suggest that glycogen is used as energy source for the contractile movements of outer hair cells.

Putative association of a mutant ROM1 allele with retinitis pigmentosa

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous form of retinal degeneration. Several genes and loci have been shown to be involved in the disease, although each of them only accounts for a few cases. Mutations in the gene encoding ROM1, a rod-specific protein, have been putatively associated with several forms of RP. Here we describe a double-mutant allele of this gene, P60T and T108M, present in two affected sibs and also in two healthy members of a Spanish RP family. The same double-mutant allele was previously considered to be responsible for autosomal dominant RP in one family. We now report data that question the potential pathogenicity of these two ROM1 mutations.

Genetics of retinoblastoma: a study

We have analyzed 43 families with either familial retinoblastoma (RB) (four kindreds), bilateral sporadic RB (10 individuals), or unilateral sporadic RB (29 individuals). Genetic studies focused on karyotype analysis, loss of heterozygosity of intragenic polymorphisms, and search for point mutations. We have been able to identify the genetic defect underlying the disease in eight cases. Deletions have been found in three patients with sporadic RB, two bilateral in one of which karyotyping had previously detected an interstitial deletion of chromosome 13 affecting (q13-q31) and one unilateral. Five different point mutations were responsible for three cases of bilateral sporadic RB, one case of bilateral sporadic RB, and one case of bilateral familial RB. The low frequency of constitutional mutations found in our study has led us to review and evaluate the possibilities and limitations of the present genetic analyses on RB and to access the different factors influencing the detection of mutations causing the disease, because genetic counseling is mainly based on mutation identification.

Clinical and genetic aspects of two Spanish families with autosomal dominant retinitis pigmentosa (ADRP)

A study was made of two families with autosomal dominant retinitis pigmentosa (ADRP) from Valencia (Spain). One family (ADRP15) was found to have mutation in codon 114 of the rhodopsin gene that led to a substitution of a glycine for an aspartic acid. The second family (ADRP7) substituted an aspartic acid for valine in codon 173 of the peripherin-RDS gene. Rhodopsin is involved in 25% of ADRP cases and many mutations of this gene have been described as causing different forms of the disease, with variable severity and age at onset. ADRP has been classified as RP with a milder symptom evolution, a typical RP fundus pattern, and macular involvement occurring after the second decade of life. Peripherin-RDS gene mutations lead to RP or other retinopathies. Furthermore, two mutations in codon 172 have been described as causing macular dystrophy. In ADRP7, a mutation in neighboring codon 173 produced RP with an atypical fundus pattern and macular involvement within the first decade of life. These observations confirm the established clinical and genetic heterogeneity involved in this form of RP.

Factor VIII gene inversions in severe hemophilia A: results of an international consortium study

Twenty-two molecular diagnostic laboratories from 14 countries participated in a consortium study to estimate the impact of Factor VIII gene inversions in severe hemophilia A. A total of 2,093 patients with severe hemophilia A were studied; of those, 740 (35%) had a type 1 (distal) factor VIII inversion, and 140 (7%) showed a type 2 (proximal) inversion. In 25 cases, the molecular analysis showed additional abnormal or polymorphic patterns. Ninety-eight percent of 532 mothers of patients with inversions were carriers of the abnormal factor VIII gene; when only mothers of nonfamilial cases were studied, 9 de novo inversions in maternal germ cells were observed among 225 cases (approximately 1 de novo maternal origin of the inversion in 25 mothers of sporadic cases). When the maternal grandparental origin was examined, the inversions occurred de novo in male germ cells in 69 cases and female germ cells in 1 case. The presence of factor VIII inversions is not a major predisposing factor for the development of factor VIII inhibitors; however, slightly more patients with severe hemophilia A and factor VIII inversions develop inhibitors (130 of 642 [20%]) than patients with severe hemophilia A without inversions (131 of 821 [16%]).

An autosomal dominant retinitis pigmentosa family with close linkage to D7S480 on 7q

Retinitis pigmentosa is the most prevalent inherited disorder of the retina. It can be autosomal dominant (adRP), autosomal recessive (arRP) or X-linked (XLRP). A form of adRP mapping to chromosome 7q was reported in a large Spanish pedigree. We have typed DNA from the members of another Spanish family for polymorphic markers from the known candidate genes. Positive lod scores were obtained only for the markers located on 7q31-35, giving a maximum lod score of 2.98 (3.01 by multipoint analysis) at theta = 0.00 for D7S480. A brief clinical evaluation is given.

Evidence against involvement of recoverin in autosomal recessive retinitis pigmentosa in 42 Spanish families

Autosomal recessive retinitis pigmentosa (ARRP) is a degenerative disease of photoreceptors in which defects in the genes encoding rhodopsin, the beta subunit of rod phosphodiesterase (PDEB) and, recently, in the gene for rod cGMP-gated channel, have been reported. However, detailed genetic involvement has not been ascertained in the great majority of cases. Recoverin, another member of the light transduction pathway, is a candidate gene for ARRP. We report the first analyses of the involvement of the recoverin gene (RCV1) in 42 Spanish ARRP families. Linkage and homozygosity studies with an intragenic polymorphism and the close markers D17S945 and D17S786 ruled out RCV1 as the cause of ARRP in 38 pedigrees. In the four remaining families, single strand conformation polymorphism analysis of the recoverin-coding region detected no mutations in the parents or in the affected members. These results strongly suggest that mutations in the RCV1 gene are not responsible for ARRP in these families.

Epidemiology of retinitis pigmentosa in the Valencian community (Spain)

The purposes of this study are to determine the frequencies of the different genetic forms of retinitis pigmentosa and to perform segregation analysis in the different genetic subtypes. Retinitis pigmentosa was diagnosed in 263 persons from 132 families. The frequency of the autosomal recessive type was the highest (31.8%) while the X-linked type was very rare (1.5%). The frequency of autosomal dominant type was 14.4% and the simplex cases constituted half of the total cases of RP registered in our community. In conclusion, in our population the high proportion of simplex cases and the low number of X-linked families are noticeable. The result of segregation analysis showed good agreement with expectation in autosomal dominant and autosomal recessive families but no more than 60% of all simplex cases were autosomal recessive. The proportion of sporadic cases was estimated statistically to be 39.9% of the total simplex cases.

Chromosome 5 abnormalities in acute lymphoblastic leukemia

We report two cases of acute lymphoblastic leukemia with involvement of chromosome 5. One of them showed a del(5)(q13q33) in a 5-year-old boy who had previously received antineoplastic chemotherapy for an L1-ALL that had been diagnosed nine months before. The other one showed a t(5;7)(q12-13;q36) together with a t(8;14)(q24;q32) and a der(1) in a 66-year-old man with an L3-ALL. Both chromosome 5 aberrations are interpreted as evolutionary events. In the first case, it was secondary to chemotherapy treatment; in the second, an evolutionary chromosome rearrangement, considering the translocation between chromosomes 8 and 14 as the primary cytogenetic event.

Gene localization in a family with X-linked syndromal mental retardation (Prieto syndrome)

A mapping study was performed on a 3-generation Spanish family with X-linked syndromal mental retardation. Affected males have a typical facial appearance, ear malformations, abnormal growth of teeth, clinodactyly, dimpled skin at the lower back, and patellar luxation. In pneumoencephalography a marked subcortical cerebral atrophy was evident. In the linkage studies with polymorphic DNA markers, no recombination was found between the disease locus and the loci OTC and DXS148, both assigned to Xp21.1. One or more recombinants were observed between the disease locus and loci from the distal part of Xp and the pericentromeric region. Close linkage to loci of Xq has also been excluded. The analysis of multiple informative meioses suggests that the disease locus maps between DXS255 (Xp11.22) and DXS84 (Xp21.1) on Xp.

Cytogenetic evidence of involvement of an early progenitor myeloid cell in 4;11 translocation-associated acute leukemia

The t(4;11)(q21;q23)-associated acute leukemia may show both lymphoid and myelomonocytic features, which suggests a pluripotent progenitor stem cell as the hematopoietic cell involved in this neoplastic process. However, there is no cytogenetic evidence to support this contention. We present a case of acute myelomonocytic leukemia (M4, FAB subtype) with t(4;11)(q21;q23), which was also found in several hypertetraploid metaphases probably corresponding to megakaryocytes. This confirms the cellular origin in an early progenitor myeloid cell of this type of acute leukemia.