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Biomedical subjects

V C Sheffield

Publications and source records attributed to V C Sheffield.

At least 91 records · Page 5Linked to original sources
PubMed1997

Homozygosity mapping of achromatopsia to chromosome 2 using DNA pooling.

Achromatopsia is an autosomal recessive disease of the retina, characterized clinically by an inability to distinguish colors, impaired visual acuity, nystagmus and photophobia. A genome-wide search for linkage was performed using an inbred Jewish kindred from Iran. To facilitate the genome-wide search, we utilized a DNA pooling strategy which takes advantage of the likelihood that the disease in this inbred kindred is inherited by all affected individuals from a common founder. Equal molar amounts of DNA from all affected individuals were pooled and used as the PCR template for short tandem repeat polymorphic markers (STRPs). Pooled DNA from unaffected members of the kindred was used as a control. A reduction in the number of alleles in the affected versus control pool was observed at several loci. Upon genotyping of individual family members, significant linkage was established between the disease phenotype and markers localized on chromosome 2. The highest LOD score observed was 5.4 (theta = 0). When four additional small unrelated families were genotyped, the combined peak LOD score was 8.2. Analysis of recombinant chromosomes revealed that the disease gene lies within a 30 cM interval which spans the centromere. Additional fine-mapping studies identified a region of homozygosity in all affected individuals, narrowing the region to 14 cM. A candidate gene for achromatopsia was excluded from this disease interval by radiation hybrid mapping. Linkage of achromatopsia to chromosome 2 is an essential first step in the identification of the disease-causing gene.

Chromosome Mapping↗
PubMed1997

Familial hypomagnesemia maps to chromosome 9q, not to the X chromosome: genetic linkage mapping and analysis of a balanced translocation breakpoint.

Familial hypomagnesemia with secondary hypocalcemia (HSH) (MIM 307600) was studied in three inbred Bedouin kindreds from Israel. The three kindreds, one extended and two nuclear families, contained 13 affected individuals, 11 males and two females. Assuming that the individuals affected with hypomagnesemia shared a chromosomal region inherited from a common ancestor, we used a DNA pooling strategy in a genome-wide search for loci which show homozygosity for shared alleles in affected individuals. DNA samples from affected individuals within a single kindred were pooled and used as the template for PCR amplification of short tandem repeat polymorphic markers (STRPs). Pooled DNA from unaffected siblings and parents were used as controls. A shift towards homozygosity was observed in the affected DNA pool compared with the control pools with D9S301 (GATA7D12). Genotyping of individual DNA samples with D9S301 and several flanking markers confirmed linkage to chromosome 9 with maximum LOD scores of 3.4 (theta = 0.05), 3.7 (theta = 0) and 2.3 (theta = 0) for the three families. We have identified a 14 cM interval on chromosome 9 (9q12-9q22.2), flanked by proximal marker D9S1874 and distal marker D9S1807, within which all affected individuals from the three kindreds are homozygous for a shared haplotype. The disease segregates with a common affected haplotype in the three families, suggesting that hypomagnesemia is caused by a common ancestral mutation in these families. Although HSH has been previously reported to be X linked, these linkage data demonstrate that the disorder is an autosomal recessive disease in these kindreds. Mapping of a chromosomal breakpoint in a somatic cell line established from a patient with HSH and a balanced X;9 translocation placed the chromosomal breakpoint in a 500 kb region flanked by D9S1844 and D9S273. Identification of the gene responsible for hypomagnesemia will provide insight into the regulation of this essential cation.

Arabs↗
PubMed1997

Construction of P1-derived artificial chromosome and yeast artificial chromosome contigs encompassing the DFNB7 and DFNB11 region of chromosome 9q13-21.

DFNB7 and DFNB11, two loci for autosomal recessive nonsyndromic hearing loss (ARNSHL), have been mapped to chromosome 9q13-21 in separate consanguineous families. Using a radiation hybrid map, we have determined the correct marker order in the DFNB7/11 region and have demonstrated that the DFNB11 locus resides within a redefined DFNB7 interval. The gene(s) responsible for ARNSHL at these loci resides within an approximately 1 cM interval bounded by markers D9S1806 (centromeric) and D9S769 (telomeric). A recently discovered Indian family confirms the new telomeric boundary. To assist in the identification and cloning of candidate genes, YAC and PAC contigs were constructed. A total of 19 YAC and 23 PAC clones were utilized to span the affected region and ensure double coverage throughout. Twenty-two previously published STSs and 21 new STSs were used to determine marker order and confirm the integrity of the contig. Using a positional cloning strategy we have identified three cochlear expressed genes that map to the DFNB7/11 interval.

Chromosome Mapping↗
PubMed1997

Clinical and molecular characterization of a family affected with X-linked ocular albinism (OA1)

Thirty-one members of a family affected with X-linked ocular albinism (OA1) were studied to characterize the clinical phenotype and identify the disease-causing mutation. The family members were examined with ophthalmoscopy, electroretinography, and Goldmann perimetry. Linkage analysis was performed with markers from the OA1 locus. Exons 2 and 8 of the OA1 gene were assayed with the polymerase chain reaction (PCR). The six affected males had visual acuities ranging from 20/40 to 20/200. All had nystagmus, iris transillumination, and foveal hypoplasia. The eldest affected male had 20/40 vision and was asymptomatic. The level of the visual acuity of the affected males was not related to the degree of retinal pigmentation. All seven female carriers had normal visual function but were found to have iris transillumination defects and variable retinal pigmentary appearance ranging from minimal pigmentary disturbance, patchy and diffuse hypopigmentation, to classic 'mud-splattered' appearance. Linkage analysis was consistent with a disease-causing mutation at the OA1 locus. PCR analysis revealed a deletion which includes at least the portion of the OA1 gene between exons 2 and 8. Affected males with X-linked ocular albinism can have a visual disability that ranges from almost none to legal blindness, and the female carriers can have variable retinal pigmentary appearance. Mutation screening of the OA1 gene can be used to confirm the diagnosis in isolated males of some families, and genetic linkage analysis can be used to accurately identify carriers even when the specific mutation cannot be identified.

Adult↗
PubMed1996

Chromosomal assignment of 2900 tri- and tetranucleotide repeat markers using NIGMS somatic cell hybrid panel 2.

Two thousand nine hundred and thirty-one tri- and tetranucleotide short tandem repeat polymorphisms (STRPs) developed by the Cooperative Human Linkage Center were assigned to chromosomes using the NIGMS somatic cell hybrid mapping panel 2 and an efficient pooling strategy. Approximately 82% of all STRPs tested were assigned by this method, with 96.7% accuracy. Many of the single chromosome cell lines contained portions of additional chromosomes, confirming previous reports. The cell lines for chromosomes 6, 14, and 20 contained extensive portions of other chromosomes. Five previously unreported chromosomal contaminants were identified and are reported. A new pooling strategy was designed to minimize ambiguous assignments.

Animals↗
PubMed1996

Development of a screening set for new (CAG/CTG)n dynamic mutations.

The expansion of a (CAG/CTG)n triplet repeat has been found to be associated with at least seven genetic diseases, suggesting that this mechanism of disease may be fairly common. To accelerate the discovery of new loci containing (CAG/CTG)n triplet expansions, we have isolated numerous genomic clones containing this class of repeats. We have developed 338 sequence-tagged sites (STSs) containing (CAG/CTG)n repeat sequences. Two hundred ninety-nine STSs were unambiguously assigned to chromosomes, and 89 of the total were assigned to YACs. The 141 STSs that were developed based on (CAG/CTG)n repeats of at least seven units were genotyped on four reference CEPH individuals to estimate their polymorphic quality.

Base Sequence↗
PubMed1996

Linkage of autosomal dominant radial drusen (malattia leventinese) to chromosome 2p16-21.

OBJECTIVE: To identify the chromosomal location of the gene involved in the pathogenesis of autosomal dominant radial drusen (malattia leventinese). PATIENTS: Eighty-six members of four families affected with radial drusen; one family of American origin and three families of Swiss origin. METHODS: Family members were clinically examined for the presence of radial drusen. Affected patients and potentially informative spouses were genotyped with short tandem repeat polymorphisms distributed across the autosomal genome. The clinical and genotypic data were subjected to linkage analysis. RESULTS: Fifty-six patients were found to be clinically affected. Significant linkage was observed between the disease phenotype and markers known to lie on the short arm of chromosome 2. The maximum two-point lod score (Zmax) observed for all four families combined was 10.5 and was obtained with marker D2S378. Multipoint analysis yielded a Zmax of 12, centered on marker D2S378. The lod-1 confidence interval was 8 cM, while the disease interval defined by observed recombinants was 14 cM. CONCLUSIONS: The gene responsible for autosomal dominant radial drusen has been mapped to the short arm of chromosome 2. This is an important step toward actually isolating the disease-causing gene. In addition, this information can be used to evaluate other familial drusen phenotypes such as Doyne's macular dystrophy for a possible allelic relationship.

Adolescent↗
PubMed1996

Pendred syndrome maps to chromosome 7q21-34 and is caused by an intrinsic defect in thyroid iodine organification.

Exactly 100 years ago, in 1896, Pendred first described the association of congenital deafness with thyroid goitre (MM#274600). The incidence of Pendred syndrome is estimated at 7.5-10/100,000, and may be responsible for as much as 10% of hereditary deafness. The cause of the congenital deafness in Pendred syndrome is obscure, although a Mondini type malformation of the cochlea exists in some patients. The reason for the association between the thyroid and cochlear defects is similarly obscure, leading some investigators to suggest that the two recessive defects may be occurring together by chance in highly consanguineous families. An in vivo defect in thyroid iodine organification in Pendred syndrome patients has been reported. However, the molecular basis of this defect is unknown and the presence of an intrinsic thyroidal defect has not been conclusively demonstrated. We have adopted a genetic linkage study as a first step towards identifying the gene. The availability of an inbred Pendred syndrome kindred allowed us to utilize an efficient DNA pooling strategy to perform a genome-wide linkage search for the disease locus. In this way, we have mapped the disease locus to an approximately 9-cM interval between GATA23F5 and D7S687 on chromosome 7. In addition, we demonstrate an intrinsic thyroid iodine organification defect in a patient's thyroid cells as the cause of the thyroid dysfunction.

Chromosome Mapping↗
PubMed1996

Localization of the Usher syndrome type ID gene (Ush1D) to chromosome 10.

The Usher syndromes (USH) are a group of autosomal recessive diseases characterized by progressive pigmentary retinopathy and sensorineural hearing loss. Five USH genes have been mapped and at least one additional gene is known to exist. By homozygosity mapping in a consanguineous family, a sixth USH gene has been localized. Clinical findings in the four affected children are consistent with established diagnostic criteria for Ush1. Linkage to known USH loci was excluded, and using two genomic DNA pools, one from the affected children and the other from the parents, 161 polymorphic markers evenly spaced across the autosomal human genome were screened. The location of the Ush1D gene was defined by the only region showing homozygosity by descent in the affected siblings, a 15 cM interval on chromosome 10q bounded by D10S529 and D10S573.

Chromosome Mapping↗
PubMed1996

A cerebellar ataxia locus identified by DNA pooling to search for linkage disequilibrium in an isolated population from the Cayman Islands.

A non-progressive recessive cerebellar ataxia was identified in a highly inbred Cayman island population. Cayman cerebellar ataxia is characterized by marked psychomotor retardation, and prominent cerebellar dysfunction manifested by nystagmus, intention tremor, dysarthric speech, and an ataxic gait. In this study, we identify linkage to chromosome 19p 13.3 using pooled DNA samples of affected individuals from an isolated population as PCR template for a genome wide screen with short tandem repeat markers. Our data demonstrate that the DNA pooling approach to identify disease gene loci is feasible using individuals from isolated populations in which kindred relationships are highly complex and exact relationships between all affected individuals are not known. Genetic fine mapping demonstrates that the genetic disease interval is approximately 9 cM, but contained within a small physical region. The existence of multiple individuals that are recombinant with flanking markers indicates that the disease interval can be further narrowed with additional markers.

Animals↗
PubMed1996

A gene for autosomal dominant late-onset progressive non-syndromic hearing loss, DFNA10, maps to chromosome 6.

Late-onset non-syndromic hearing impairment is the most common type of neurological dysfunction in the elderly. It can be either acquired or inherited, although the relative impact of heredity on this type of loss is not known. To date, nine different genes have been localized, but none has been cloned. Using an extended American family in which a gene for autosomal dominant late-onset non-syndromic hearing impairment is segregating, we have identified a new locus, DFNA10, on chromosome 6.

Chromosome Mapping↗
PubMed1996

Autosomal dominant Charcot-Marie-Tooth axonal neuropathy mapped on chromosome 7p (CMT2D).

Clinical, electrophysiological and genetic linkage studies were performed on a large autosomal dominant family with Charcot-Marie-Tooth axonal neuropathy type 2 (CMT2) with 38 members of which 14 were affected. Onset of the disease was between 16 and 30 years of age with weakness and atrophy of the hands more severe than of the feet with slow progressive course in 12 patients. Deep tendon reflexes were absent in the upper extremities and decreased in the lower extremities. There was distal hypesthesia for touch, proprioception and vibration sense for the hands more than for the feet. Motor nerve conduction velocities showed normal values (48-53 M/s) with normal latencies (2-3 msec) and electromyography revealed signs of denervation. Genetic linkage analysis used 167 short tandem repeat markers (STRPs) spaced throughout the 22 autosomes. Linkage to the short arm of chromosome 7 at 7p14 was found using the marker D7S435 (Z = 4.83 at theta = 0). Flanking markers were D7S1808 and D7S1806 and the genetic distance between them was 6.8 cM. The multipoint linkage analysis gave a peek multipoint lod score of 6.89 between the markers D7S1808 and D7S435. Linkage analysis showed significantly negative lod scores (with values less than -2) with markers of chromosomes 1 and 3 where CMT axonal forms have been previously mapped. PFGE analysis indicated the absence of the CMT1A duplication. Our findings are consistent with a new genetic type of axonal CMT neuropathy designated by us as CMT2D. Potential candidate genes are multiple T-cell gamma receptor genes which map to the same cytogenetic interval as CMT2D neuropathy.

Charcot-Marie-Tooth Disease↗
PubMed1996

Fine mapping of the autosomal dominant juvenile open angle glaucoma (GLC1A) region and evaluation of candidate genes.

Juvenile Open Angle Glaucoma (GLC1A) is an autosomal optic neuropathy that has been localized previously to chromosome 1q. Here we report the fine mapping of the disease region using YACs and a high density of polymorphic microsatellite markers. This study utilized two large JOAG pedigrees genotyped at 36 loci from chromosome 1q21-q31 to refine the GLC1A locus to a approximately 3-cM region flanked by YAC-derived microsatellite markers D1S3665 and D1S3664. The candidate genes LAMC1, NPR1, and CNR2 were excluded from the region by linkage. Four other genes, SELE, SELL, TXGP1, and APT1LG1, were determined to lie within the critical region through YAC content and linkage mapping. The YAC-STS content map of the critical region provides the groundwork for the construction of a transcription map and the identification of the disease-causing gene.

Child↗
PubMed1996

Full characterization of the maculopathy associated with an Arg-172-Trp mutation in the RDS/peripherin gene.

The objective of this study was to fully characterize the macular dystrophy phenotype and genotype in a large family of the Zermatt area of Switzerland. Clinical and molecular studies of the family included a comprehensive eye examination and a mutational analysis of the RDS, rhodopsin, and TIMP-3 genes. In selected cases, fluorescein angiography, perimetry, and electroretinography were performed. Forty-two family members at risk of expressing the maculopathy were studied. Of these, 24 were found to be clinically affected. The severity of macular disease in these patients was clearly age-related and different stages of progression were identified. Central pigmentary alterations were seen in adolescent patients, while patients in their late teens and twenties exhibited drusen-like deposits. Later, these defects formed focal areas of atrophy which eventually led to central geographic atrophy with severe visual loss by the fifth decade and cone-rod dysfunction. The transmission of this condition is autosomal dominant with complete penetrance. The underlying genetic defect is a mutation in codon 172 of the RDS/peripherin gene, a gene expressed in both rods and cones, which results in the substitution of tryptophan for an arginine residue at that position. 'Zermatt macular dystrophy' is a dominant, age-related, progressive macular dystrophy which in later stages resembles atrophic age-related macular degeneration. The size of the family studied allowed definition of the clinical spectrum of this condition and identification of the related genetic defect which allows more precise diagnosis and counseling.

Adult↗
PubMed1996

Photoreceptor function in heterozygotes with insertion or deletion mutations in the RDS gene.

PURPOSE: To understand the pathophysiology of human retinal degenerations caused by mutations in the peripherin/RDS gene. METHODS: Three families with autosomal dominant retinal degeneration were found to have mutations in the peripherin/RDS gene. There were two frameshift mutations: a 1-base pair (bp) insertion at codon 32 and a 2-bp deletion at codon 193. For these mutations, the predicted proteins would be truncated by 303 and 131 amino acids, respectively. The third mutation would result in an 8-bp substitution for five nucleotides involving codons 67-69 and would be predicted to disrupt the second transmembrane domain of the protein. Heterozygotes were examined clinically and with rod and cone perimetry, dark adaptometry, and rod- and cone-isolated electroretinograms (ERGs). RESULTS: Rod and cone sensitivity losses were present with perimetric testing in most patients; patients with advanced disease in all three families showed more pericentral than peripheral field dysfunction. The kinetics of dark adaptation were abnormal in all patients. Rod and cone ERG a-waves were normal in maximum amplitude in three younger patients but were reduced in all others; phototransduction was normal in most patients. There was equal loss of rod and cone a-wave amplitudes and equal elevation of rod and cone thresholds. CONCLUSIONS: Heterozygotes with these different peripherin/RDS gene mutations showed variation in clinical presentation but a similar pattern of receptor abnormalities. Results of visual function tests were consistent with a normal amount of rod and cone outer segment membrane in early disease, progressing to reduced outer segments at later stages. There was an equal effect on rod and cone photoreceptor function at all stages of disease. This functional phenotype may represent the human analogue of the rds/+ mouse.

Adolescent↗
PubMed1996

An autosomal recessive nonsyndromic-hearing-loss locus identified by DNA pooling using two inbred Bedouin kindreds.

Autosomal recessive nonsyndromic hearing loss (ARNSHL) is the most common form of severe inherited childhood deafness. We present the linkage analysis of two inbred Bedouin kindreds from Israel that are affected with ARNSHL. A rapid genomewide screen for markers linked to the disease was performed by using pooled DNA samples. This screen revealed evidence for linkage with markers D9S922 and D9S301 on chromosome 9q. Genotyping of individuals from both kindreds confirmed linkage to chromosome 9q and a maximum combined LOD score of 26.2 (recombination fraction [theta] .025) with marker D9S927. The disease locus was mapped to a 1.6-cM region of chromosome 9ql3-q2l, between markers D9S15 and D9S927. The disease segregates with a common haplotype in the two kindreds, at markers D9S927, D9S175, and D9S284 in the linked interval, supporting the hypothesis that both kindreds inherited the deafness gene from a common ancestor. Although this nonsyndromic-hearing-loss (NSHL) locus maps to the same cytogenetic interval as DFNB7, it does not overlap the currently defined DFNB7 interval and may represent (1) a novel form of NSHL in close proximity to DFNB7 or (2) a relocalization of the DFNB7 interval to a region telomeric to its reported location. This study further demonstrates that DNA pooling is an effective means of quickly identifying regions of linkage in inbred families with heterogeneous autosomal recessive disorders.

Arabs↗