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Biomedical subjects

M B Davis

Publications and source records attributed to M B Davis.

At least 19 recordsLinked to original sources
PubMed2004

Hereditary motor and autonomic neuronopathy 1 maps to chromosome 20q13.2-13.3.

The spinal muscular atrophies (SMA) or hereditary motor neuronopathies result from the continuous degeneration and death of spinal cord lower motor neurons, leading to progressive muscular weakness and atrophy. We describe a large Brazilian family exhibiting an extremely rare, late-onset, dominant, proximal, and progressive SMA accompanied by very unusual manifestations, such as an abnormal sweating pattern, and gastrointestinal and sexual dysfunctions, suggesting concomitant involvement of the autonomic nervous system. We propose a new disease category for this disorder, 'hereditary motor and autonomic neuronopathy', and attribute the term, 'survival of motor and autonomic neurons 1' (SMAN1) to the respective locus that was mapped to a 14.5 cM region on chromosome 20q13.2-13.3 by genetic linkage analysis and haplotype studies using microsatellite polymorphic markers. This locus lies between markers D20S120 and D20S173 showing a maximum LOD score of 4.6 at D20S171, defining a region with 33 known genes, including several potential candidates. Identifying the SMAN1 gene should not only improve our understanding of the molecular mechanisms underlying lower motor neuron diseases but also help to clarify the relationship between motor and autonomic neurons.

Chromosome Mapping↗
PubMed2004

Creation of EcR isoform-specific mutations in Drosophila melanogaster via local P element transposition, imprecise P element excision, and male recombination.

Collections of single P transposable-element insertion strains that currently inactivate more than 25% of essential Drosophila genes have proven to be a valuable tool for genome research in Drosophila melanogaster. For genes unrepresented in these collections, strategies including local P element transposition and transposase-induced imprecise excision can be used to inactivate or delete the gene of interest. Here we report our use of local P element transposition followed by imprecise P element excision and transposase-induced male recombination to generate two deficiencies specific for the EcR-A isoform of the ecdysone receptor ( EcR) gene, and four larger deficiencies likely to affect multiple EcR functions. We also report here the determination of sequences flanking six EcR-B deficiencies generated in a previous imprecise excision screen. EcR-A encodes one of a family of three related nuclear receptor proteins that, together with the heterodimer partner USP, mediate ecdysone signaling during Drosophila development. Our results delineate sequences required in vivo for EcR-A function, as well as identifying EcR-A intron 1 sequences that are not essential for EcR function.

Animals↗
PubMed2004

Spinocerebellar ataxia and hypergonadotropic hypogonadism associated with familial sensorineural hearing loss.

Cerebellar ataxia has been described as being associated with hypogonadism for almost 100 years. In the majority of cases, hypogonadism is hypogonadotropic. The association of cerebellar ataxia with hypergonadotropic hypogonadism is a rare genetic disorder with a recessive mode of inheritance. Cerebellar ataxia and hypogonadism can also occur associated with a large spectrum of additional clinical manfestations, including mental retardation, sensorineural deafness, choroidal dystrophy, ectodermal dysplasia and short stature, and polyneuropathy. We report the case of a woman with early-onset spinocerebellar ataxia, primary amenorrhea due to hypergonadotropic hypogonadism, and late-onset sensorineural hearing loss. Additional family members from the father's side are affected with late-onset hearing loss, suggesting a dominant mode of inheritance.

Adult↗
PubMed2004

Autosomal dominant cerebellar ataxia: SCA2 is the most frequent mutation in eastern India.

OBJECTIVE: Spinocerebellar ataxia type 2 (SCA2) has been reported as the commonest dominant hereditary ataxia in India. However, India is an ethnically and religiously diverse population. Previous studies have not clearly indicated exact ethnic and religious origins, and must therefore be interpreted with caution. The purpose of this study was to determine the prevalence of different SCA mutations in a relatively homogeneous population from eastern India. METHODS: We identified 28 families with autosomal dominant cerebellar ataxia from eastern India. Each underwent full clinical evaluation and were analysed for the presence of SCA1, SCA2, SCA3, SCA6, SCA7, SCA8, SCA12, and SCA17 mutations. In addition, haplotype analysis was carried out in seven of the 16 families with SCA2. RESULTS: Seven patients from four (14%) families were positive for an expansion in SCA1 and 26 patients from 16 (57%) families were positive for an expansion in SCA2. No mutations were detected in the remaining eight families (29%). Most of the SCA1 and SCA2 families were Hindu from the state of Bihar. Five out of 26 SCA2 patients in this study did not have slow saccades. In addition, four of seven SCA1 patients had slow saccades. We found an association between the SCA2 CAG repeat expansion and the 285 base pair (bp) allele of microsatellite marker D12S1672, and also data supportive of the association between the expansion and the 225 bp allele of D12S1333, which has been previously described. CONCLUSIONS: We conclude that (1) although slow ocular saccades are highly suggestive of SCA2, that they are not universal, nor are they exclusive to this disorder and (2) SCA2 is likely to be the commonest dominant ataxia in eastern India, with further evidence for a founder effect.

Adolescent↗
PubMed2002

PARK6 is a common cause of familial parkinsonism.

The Parkin gene is responsible for about 50% of autosomal recessive juvenile parkinsonism (ARJP) and less than 20% of sporadic early onset cases. We recently mapped a novel ARJP locus (PARK6) on chromosome 1p. Linkage to PARK6 was confirmed in 8 families from 4 different European countries. These families share some clinical features with the European Parkin-positive cases, with a wide range of ages at onset and slow progression. However, features typical of ARJP, such as dystonia and sleep benefit, were not observed, making the clinical presentation of late-onset cases indistinguishable from that of idiopathic PD. The determination of the smallest region of homozygosity in one consanguineous family allowed reducing the candidate interval to 9 cM. PARK6 appears to be an important locus for ARJP in Europe.

Chromosomes, Human, Pair 1↗
PubMed2002

Two large British kindreds with familial Parkinson's disease: a clinico-pathological and genetic study.

We present the findings of a study of two large unrelated kindreds with autosomal dominant Parkinson's disease. The affected members were assessed clinically and with [(18)F]6-fluorodopa-PET and were indistinguishable from patients with the sporadic form of Parkinson's disease. In one kindred, an affected member was examined subsequently at autopsy and Lewy bodies were present in a distribution typical of sporadic Parkinson's disease. These kindreds are distinct from other Parkinsonian kindreds with identified genetic loci (PARK1-4) and provide further evidence for genetic heterogeneity in familial Parkinson's disease.

Adult↗
PubMed2001

Mechanical evidence of cervical facet capsule injury during whiplash: a cadaveric study using combined shear, compression, and extension loading.

STUDY DESIGN: A comparison of cervical facet capsule strain fields in cadaveric motion segments exposed to whiplash-like loads and failure loads. OBJECTIVES: To compare the maximum principal strain in the facet capsular ligament under combined shear, bending, and compressive loads with those required to injure the ligament. SUMMARY OF BACKGROUND DATA: The cervical facet capsular ligament is thought to be an anatomic site for whiplash injury, although the mechanism of its injury remains unclear. METHODS: Motion segments from seven female donors were exposed to quasi-static flexibility tests using posterior shear loads of 135 N applied to the superior vertebra under four compressive axial preloads up to 325 N. The right facet joint was then isolated and failed in posterior shear loading. The Lagrangian strain field in the right facet capsular ligament was calculated from capsular displacements determined by stereophotogrammetry. Statistical analyses examined the effect of axial compression on motion segment flexibility, and compared maximum principal capsular strain between the flexibility and failure tests. RESULTS: Capsular strain increased with applied shear load but did not vary with axial compressive load. The maximum principal strain reached during the flexibility tests was 61% +/- 33% of that observed in subcatastrophic failures of the isolated joints. Two specimens reached strains in their flexibility tests that were larger than their corresponding strains at subcatastrophic failure in the failure tests. CONCLUSIONS: The cervical facet capsular ligaments may be injured under whiplash-like loads of combined shear, bending, and compression. The results provide a mechanical basis for injury caused by whiplash loading.

Cadaver↗
PubMed2001

Range shifts and adaptive responses to Quaternary climate change.

Tree taxa shifted latitude or elevation range in response to changes in Quaternary climate. Because many modern trees display adaptive differentiation in relation to latitude or elevation, it is likely that ancient trees were also so differentiated, with environmental sensitivities of populations throughout the range evolving in conjunction with migrations. Rapid climate changes challenge this process by imposing stronger selection and by distancing populations from environments to which they are adapted. The unprecedented rates of climate changes anticipated to occur in the future, coupled with land use changes that impede gene flow, can be expected to disrupt the interplay of adaptation and migration, likely affecting productivity and threatening the persistence of many species.

Adaptation, Physiological↗
PubMed2001

Identification of a novel primary torsion dystonia locus (DYT13) on chromosome 1p36 in an Italian family with cranial-cervical or upper limb onset.

Primary torsion dystonia (PTD) is a clinically and genetically heterogeneous group of movement disorders, usually inherited in an autosomal dominant fashion. Three PTD loci (DYT1, DYT6 and DYT7) have been identified to date. However, in several PTD families linkage to the known loci has been excluded. We identified an Italian PTD family with 11 definitely affected members. Phenotype was characterised by juvenile or early-adult onset, prominent cranial-cervical and upper limb involvement, mild course and occasional generalisation. A genome-wide search performed in the family identified a novel PTD locus (DYT13) within a 22-cM interval on the short arm of chromosome 1, with a maximum lod score of 3.44 (theta = 0) between the disease and marker D1S2667.

Adolescent↗
PubMed2001

Genetics of Parkinsonism: a review.

Idiopathic Parkinson's disease (IPD), a progressive neurodegenerative disorder, is a common cause of disability. No current therapies modify disease progression. The pathological hallmarks are the presence of Lewy bodies and massive loss of dopaminergic neurons in the pars compacta of the substantia nigra. Two genes (SNCA and parkin) as well as two gene loci have now been implicated in the pathogenesis of familial PD. These represent significant progress in our understanding of the disease, considering the rarity of large families, low heritability in the general population and genetic heterogeneity. Mutations in a further gene, UCHL1, have been described in familial PD although the evidence for its role in PD is less clear. Knowledge of the genes described in PD to date should help to define molecular mechanisms of neurodegeneration in PD, as well as in other diseases where defects in protein handling may be a common feature. Nigral degeneration with Lewy body formation and the resulting clinical picture of PD may represent a final common pathway of a multifactorial disease process in which both environmental and genetic factors have a role. This review discusses the major advances in the field to date and illustrates how the existence of genetic factors has now become firmly established.

Humans↗
PubMed2001

Positive and negative intronic regulatory elements control muscle-specific alternative exon splicing of Drosophila myosin heavy chain transcripts.

Alternative splicing of Drosophila muscle myosin heavy chain (MHC) transcripts is precisely regulated to ensure the expression of specific MHC isoforms required for the distinctive contractile activities of physiologically specialized muscles. We have used transgenic expression analysis in combination with mutagenesis to identify cis-regulatory sequences that are required for muscle-specific splicing of exon 11, which is encoded by five alternative exons that produce alternative "converter" domains in the MHC head. Here, we report the identification of three conserved intronic elements (CIE1, -2, and -3) that control splicing of exon 11e in the indirect flight muscle (IFM). Each of these CIE elements has a distinct function: CIE1 acts as a splice repressor, while CIE2 and CIE3 behave as splice enhancers. These CIE elements function in combination with a nonconsensus splice donor to direct IFM-specific splicing of exon 11e. An additional cis-regulatory element that is essential in coordinating the muscle-specific splicing of other alternative exon 11s is identified. Therefore, multiple interacting intronic and splice donor elements establish the muscle-specific splicing of alternative exon 11s.

Alternative Splicing↗
PubMed2001

DYT13, a novel primary torsion dystonia locus, maps to chromosome 1p36.13--36.32 in an Italian family with cranial-cervical or upper limb onset.

Primary torsion dystonia (PTD) is a clinically and genetically heterogeneous group of movement disorders, usually inherited in an autosomal dominant fashion with reduced penetrance. The DYT1 gene on chromosome 9q34 is responsible for most cases of early limb-onset PTD. Two other PTD loci have been mapped to date. The DYT6 locus on chromosome 8 is associated with a mixed phenotype, whereas the DYT7 locus on chromosome 18p is associated with adult onset focal cervical dystonia Several families have been described in which linkage to the known PTD loci have been excluded. We identified a large Italian PTD family with 11 definitely affected members. Phenotype was characterized by prominent cranial-cervical and upper limb involvement and mild severity. A genome-wide search was performed in the family. Linkage analysis and haplotype construction allowed us to identify a novel PTD locus (DYT13) within a 22 cM interval on the short arm of chromosome 1, with a maximum lod score of 3.44 between the disease and marker D1S2667.

Adolescent↗
PubMed2000

The development of the nociceptive responses in neurokinin-1 receptor knockout mice.

An important yet unanswered question is how neonates respond to painful stimuli, given the immaturity of their neural pathways. We examined the development of the neurokinin system using a novel approach, examining changes of this system by observing the pain responses of mice lacking the NK1 receptor at different stages of development We show that the NK1 receptor is not involved in nociception to heat, mechanical or chemical stimuli, at 3 days. In contrast, the NK1 receptor is involved in nociceptive responses to high intensity heat and mechanical stimuli, and mediates the second phase of the formalin response in 21-day-old mice. This indicates that nociception in neonates does not require the NK1 receptor and that the functional maturation of the NK1 receptor allows diversity in both the type of stimuli that activate the pain system and the types of responses elicited by nociceptive stimuli.

Aging↗
PubMed2000

A Yorkshire family with adult-onset cranio-cervical primary torsion dystonia.

Although a family history is described in approximately 20% of patients, large families with adult-onset craniocervical primary (idiopathic) torsion dystonia (PTD) are rare. We report a new British family with cranio-cervical dystonia. Seventeen members of the family were examined. Five cases were diagnosed as definite PTD and one as probable PTD. Mean age at onset was 29 years (range, 19-40 yrs). The phenotype was characterized by adult-onset cranio-cervical dystonia in all affected cases. A few cases had additional voice tremor and/or postural arm tremor. The GAG deletion in the DYT1 gene was excluded in the index case. Linkage analysis was performed between the disease and several marker loci spanning DYT6 and DYT7 regions, and haplotypes were reconstructed in all subjects. Although linkage analysis was not completely informative, reconstructed haplotypes excluded linkage between the disease and either DYT6 or DYT7. This report confirms that familial cranio-cervical dystonia is genetically heterogeneous, and further studies of other PTD families with similar clinical features are needed to identify other new genes.

Adult↗
PubMed2000

A second paroxysmal kinesigenic choreoathetosis locus (EKD2) mapping on 16q13-q22.1 indicates a family of genes which give rise to paroxysmal disorders on human chromosome 16.

Paroxysmal kinesigenic choreoathetosis (PKC) is a rare paroxysmal movement disorder characterized by recurrent and brief attacks of choreiform or dystonic movements triggered or exacerbated by sudden voluntary movements. Some patients with PKC also have a history of infantile afebrile convulsions. PKC can be sporadic, or familial with autosomal dominant inheritance. PKC has been mapped to the pericentromeric region of human chromosome 16 in several Japanese families and in an African-American family, to regions which overlap by 9.8 cM (centiMorgan). Both regions overlap by 3.4 cM with a region containing a gene responsible for 'infantile convulsions and paroxysmal choreoathetosis' (ICCA). We have identified a second PKC locus (EKD2) on the long arm of chromosome 16 in a large Indian family with PKC. A maximum two-point LOD score of 3.66 (recombination fraction = 0.00, penetrance = 0.80) was obtained between PKC and D16S419. Haplotype and recombinant analysis localized EKD2 to a 15.8 cM region between D16S685 and D16S503. This region does not overlap with that identified in Japanese families, or with the ICCA locus. These results exclude one locus on chromosome 16 which causes both the ICCA and PKC syndromes; this suggests that there may be a cluster of genes on human chromosome 16 which lead to paroxysmal disorders.

Adolescent↗
PubMed1999

Participation of the melanocortin-1 receptor in the UV control of pigmentation.

The cloning of the melanocortin-1 receptor (MC1R) gene from human melanocytes and the demonstration that these cells respond to the melanocortins alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH) with increased proliferation and melanogenesis have renewed the interest in investigation the physiological role of these hormones in regulating human pigmentation. Alpha-melanocyte stimulating hormone and ACTH are both synthesized in the human epidermis, and their synthesis is upregulated by exposure to ultraviolet radiation (UVR). Activation of the MC1R by ligand binding results in stimulation of cAMP formation, which is a principal mechanism for inducing melanogenesis. The increase in cAMP is required for the pigmentary response of human melanocytes to UVR, and for allowing them to overcome the UVR-induced G1 arrest. Treatment of human melanocytes with alpha-MSH increases eumelanin synthesis, an effect that is expected to enhance photoprotection of the skin. Population studies have revealed more than 20 allelic variants of the MC1R gene. Some of these variants are overexpressed in individuals with skin type I or II, red hair, and poor tanning ability. Future studies will aim at further exploration of the role of these variants in MC1R function, and in determining constitutive human pigmentation, the response to sun exposure, and possibly the susceptibility to skin cancer.

Alleles↗