Bardet-Biedl syndrome is linked to DNA markers on chromosome 11q and is genetically heterogeneous.

Bardet-Biedl syndrome (BBS) is an uncommon autosomal recessive condition characterized by mental retardation, post-axial polydactylia, obesity and pigmentary retinopathy. We performed linkage analysis in 31 multiplex BBS families and report significant linkage with two markers on chromosome 11q, PYGM and AFM164zf12 (D11S913). Homogeneity testing demonstrates genetic heterogeneity within our set of families. Our data imply that a major gene, BBS1, is located on chromosome 11q, although mutations at other loci may also be associated with this phenotype.

Description of a second microsatellite marker and linkage analysis of the muscle glycogen synthase locus in familial NIDDM.

Non-insulin-dependent diabetes mellitus (NIDDM) is characterized by impaired insulin-stimulated glucose uptake into glycogen. Both biochemical and genetic data have implicated glycogen synthase as a candidate for the genetic predisposition to diabetes. To test this hypothesis, we isolated cosmid clones containing genomic DNA for the glycogen synthase (GSY) gene and identified a region of 20 GT repeat units in a clone that extended 15 kilobases 3' to the gene. This region was highly polymorphic with nine alleles (heterozygosity 0.74). With the use of this polymorphism, the GSY was mapped on chromosome 19q between markers D19S217 and D19S210 and at theta = 0.036 from the histidine-rich calcium-binding protein (HRC) locus. Linkage to GSY was rejected under multiple models with logarithm of odds (LOD) scores of -1.36 to -5.22. In contrast, we could not reject linkage under dominant and intermediate (additive) models for the HRC locus (maximum LOD scores 1.51 and 1.54), despite the close proximity to GSY. Multipoint analysis of NIDDM versus GSY and HRC placed the putative diabetes locus centromeric to HRC and away from GSY. Furthermore, analysis of the previously associated Xba I polymorphism suggested neither linkage nor sib-pair sharing. We conclude that mutations of the GSY gene are unlikely to play a major role in the predisposition to NIDDM in our families. However, we cannot exclude a modifying role in a polygenic disorder or an important role in some families. The moderately positive LOD scores near the HRC locus suggest a need for evaluation of this region in additional NIDDM families.

Genetic mapping of adrenergic receptor genes in humans.

We have genetically mapped the genes encoding four human adrenergic receptors (ARs) of subtypes alpha 1C, alpha 2A, alpha 2B, and beta 1, which are prototypic G protein coupled receptors that mediate the physiological effects of neurotransmitters, hormones, and drugs. We placed these genes onto the Cooperative Human Linkage Center (CHLC) and Genethon framework maps, within confidence intervals with greater than 1000:1 odds. With multipoint analysis the alpha 1C gene (locus ADRA1C) mapped to the interval between NEFL and D8S283; alpha 2-C4, the gene encoding the alpha 2C AR (locus ADRA2C), mapped to the interval between D4S126 and D4S62; and the alpha 2-C10 (alpha 2A AR)/beta 1 haplotype (loci ADRA2A/ADRB1) mapped to the interval between D10S259 and D10S187. A fifth AR gene, beta 2, yielded significant LOD scores with markers on the long arm of chromosome 5; however, this locus (ADRB2) could not be mapped to any specific interval with odds of greater than 1000:1. The two AR genes that are completely linked, alpha 2-C10 and beta 1, were oriented on their shared 225-kb genomic fragment relative to the direction of transcription, with beta 1 being 5' to alpha 2-C10. The positioning of these genes on high-density framework maps allows them to be tested as candidates in a spectrum of diseases that might involve AR dysfunction.

Aminoaciduria in chronic renal failure--its relationship to vitamin D and parathyroid status.

Fractional clearances of amino acids in 24 patients with chronic renal failure indicate that aminoaciduria is common and often severe. Eleven studies have also been carried out in ten patients with stable renal failure before and during treatment with different metabolites of vitamin D. Sequential measurements of fractional clearance of amino acids, plasma 25-hydroxy-vitamin D (25-(OH)D) and serum parathyroid hormone were made. All patients initially had hyperaminoaciduria, secondary hyperparathyroidism and osteomalacia. Treatment with 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) or 1 alpha-hydroxycholecalciferol (1 alpha(OH)D3) significantly improved amino acid reabsorption irrespective of the initial degree of aminoaciduria. Cholecalciferol or 25-hydroxycholecalciferol(25(OH)D3) improved amino acid transport in patients with initially mild hyperaminoaciduria, but not in patients with severe hyperaminoaciduria. Reduction in aminoaciduria during treatment with 25(OH)D3 may have depended on a variable ability to synthesize 1,25(OH)2D3. Changes in amino acid transport did not correlate with changes in serum parathyroid hormone. It is suggested that defective amino acid reabsorption in patients with chronic renal failure is due at least in part to deficiency of 1,25(OH)2D3.

Hereditary spastic paraplegia linked to chromosome 15q: Analysis of candidate genes.

We previously reported an extended kindred with autosomal dominant uncomplicated hereditary spastic paraplegia (HSP) and found close linkage between the disorder and microsatellite polymorphisms on chromosome 15q. Multipoint linkage analysis reached a maximum LOD score (10.16) between D15S128 and D15S156, a region that includes genes encoding alpha5 and beta3 subunits of GABAA receptor. Theoretically, abnormal GABA-mediated neurotransmission could produce spasticity and possibly other changes of HSP. We used genetic linkage analysis to evaluate these two HSP candidate genes and observed obligate recombinants for polymorphisms immediately adjacent to (or within untranslated regions of) genes encoding alpha5 and beta3 GABAA receptor subunits. Although these genes are linked tightly to the HSP locus, our findings conclusively exclude these genes from being responsible for HSP in this kindred.

Autosomal dominant, familial spastic paraplegia, type I: clinical and genetic analysis of a large North American family.

"Familial spastic paraplegia" (FSP) refers to clinically and genetically diverse syndromes characterized by insidiously progressive lower extremity spasticity. We evaluated 126 members of a large kindred, including 31 affected subjects, in which FSP was transmitted as a stereotyped, autosomal dominant disorder that showed complete genetic penetrance. Affected subjects developed insidiously progressive gait disturbance between ages 12 and thirty-five. Neurologic examination revealed hyperreflexia and spasticity in the lower extremities, weakness of hip flexion and ankle dorsiflexion, extensor plantar response, diminished vibratory sense in the feet, and pes cavus. Using genetic linkage analysis, we excluded the FSP1 locus on chromosome 14q11.2 as the disease locus in this family. We present the clinical and genetic features of FSP type I, including the age-adjusted risk of developing the disorder in this family.

Genetic linkage of the dentinogenesis imperfecta type III locus to chromosome 4q.

Dentinogenesis imperfecta type III (DGI-III) is an autosomal-dominant disorder of dentin formation which appears in a tri-racial southern Maryland population known as the "Brandywine isolate". This disease has suggestive evidence of linkage to the long arm of human chromosome 4 (LOD score of 2.0) in a family presenting with both juvenile periodontitis and DGI-III. The purpose of this study was to screen a family presenting with only DGI-III to determine if this locus was indeed on chromosome 4q. Furthermore, we wanted to determine if DGI-III co-localized with dentinogenesis imperfecta type II (DGI-II), which has been localized to 4q21-q23. Therefore, a large kindred from the Brandywine isolate was identified, oral examination performed, and blood samples collected from 21 family members. DNA from this family was genotyped with 6 highly polymorphic markers that span the DGI-II critical region of chromosome 4q. Analysis of the data yielded a maximum two-point LOD score of 4.87 with a marker for the dentin matrix protein 1 (DMP1) locus, a gene contained in the critical region for DGI-II. Our results demonstrated that the DGI-III locus is on human chromosome 4q21 within a 6.6 cM region that overlaps the DGI-II critical region. These results are consistent with the hypothesis that DGI-II is either an allelic variant of DGI-III or the result of mutations in two tightly linked genes.

A gene for primary congenital glaucoma is not linked to the locus on chromosome 1q for autosomal dominant juvenile-onset open angle glaucoma.

BACKGROUND: Primary congenital glaucoma is an uncommon autosomal recessive condition that results from a developmental defect in the trabecular meshwork and anterior chamber angle, manifesting in the neonatal or infantile period with increased intraocular pressure, corneal enlargement and edema, and optic nerve cupping with consequent loss of vision. Nothing is known about its genetic location. PATIENTS AND METHODS: Linkage analysis was performed in 25 primary congenital glaucoma Saudi Arabian families with six polymorphic DNA markers on chromosome 1q in a region that has shown tight linkage to a locus for autosomal dominant juvenile-onset open angle glaucoma (GLC1A). Twenty-four of these families are highly consanguineous. RESULTS: Each family was shown separately to exclude the 8-centimorgan (cM) interval containing the GLC1A locus. Four families independently demonstrated overlapping regions of exclusion (theta < or = -2) that spanned the entire 8-cM interval. Assignment of a primary congenital glaucoma locus in this region could be excluded by a cadre of 21 families because a primary congenital glaucoma disease locus did not segregate in an autosomal recessive manner on haplotypes constructed with markers in this region. For all families, no affected individuals demonstrated homozygosity of alleles in regions tightly linked to the GLC1A locus. CONCLUSION: These results exclude the 8-cM region on chromosome 1q shown to contain the GLC1A locus from containing a disease locus for primary congenital glaucoma in this population of 25 Saudi Arabian families.

Mapping recessive ophthalmic diseases: linkage of the locus for Usher syndrome type II to a DNA marker on chromosome 1q.

Usher syndrome is a heterogeneous group of autosomal recessive disorders that combines variably severe congenital neurosensory hearing impairment with progressive night-blindness and visual loss similar to that in retinitis pigmentosa. Usher syndrome type I is distinguished by profound congenital (preverbal) deafness and retinal disease with onset in the first decade of life. Usher syndrome type II is characterized by partial hearing impairment and retinal dystrophy that occurs in late adolescence or early adulthood. The chromosomal assignment and the regional localization of the genetic mutation(s) causing the Usher syndromes are unknown. We analyzed a panel of polymorphic genomic markers for linkage to the disease gene among six families with Usher syndrome type I and 22 families with Usher syndrome type II. Significant linkage was established between Usher syndrome type II and the DNA marker locus THH33 (D1S81), which maps to chromosome 1q. The most likely location of the disease gene is at a map distance of 9 cM from THH33 (lod score 6.5). The same marker failed to show linkage in families segregating an allele for Usher syndrome type I. These data confirm the provisional assignment of the locus for Usher syndrome type II to the distal end of chromosome 1q and demonstrate that the clinical heterogeneity between Usher types I and II is caused by mutational events at different genetic loci. Regional localization has the potential to improve carrier detection and to provide antenatal diagnosis in families at risk for the disease.

Genetic susceptibility in familial multiple sclerosis not linked to the myelin basic protein gene.

The myelin basic protein (MBP) gene is a candidate locus for disease susceptibility in familial multiple sclerosis. Amplification of a polymorphic tetranucleotide repeat region immediately 5' to MBP exon 1 demonstrated the presence of eight different alleles among members of 14 multiplex multiple sclerosis families (36 affected individuals). Linkage analysis was performed with autosomal dominant and autosomal recessive models, normal individuals with abnormal magnetic resonance scans being scored as either unknown or affected. Cumulative LOD scores were negative for both models of inheritance. The results do not demonstrate linkage between the MBP gene region and multiple sclerosis.

Genetic linkage analysis in familial benign (hypocalciuric) hypercalcemia: evidence for locus heterogeneity.

Familial benign hypercalcemia (FBH, or hypocalciuric hypercalcemia) is characterized by inheritance, in an autosomal dominant pattern, of lifelong hypercalcemia without hypercalciuria, which is often mistaken for classical primary hyperparathyroidism. Recently, the FBH trait was linked, in four families, to chromosome 3q. We report genetic linkage analysis in 140 persons from five additional families having FBH (65 affected, 67 unaffected, and 8 unclassifiable). In four families, FBH mapped to chromosome 3q, between D3S1215 and D3S20, maximum multipoint lod score 12.9. By contrast, in the fifth kindred FBH mapped to chromosome 19p13.3, tightly linked to the marker loci D19S20 and D19S266 (two-point lod score at recombination fraction = .001 is 3.44 and 3.70, respectively). Thus, the FBH phenotype results from mutations at two separate loci on chromosomes 3q and 19p.

Autosomal dominant spinocerebellar ataxia with sensory axonal neuropathy (SCA4): clinical description and genetic localization to chromosome 16q22.1.

The hereditary ataxias represent a clinically and genetically heterogeneous group of neurodegenerative disorders. Various classification schemes based on clinical criteria are being replaced as molecular characterization of the ataxias proceeds; so far, seven distinct autosomal dominant hereditary ataxias have been genetically mapped in the human genome. We report linkage to chromosome 16q22.1 for one of these genes (SCA4) in a five-generation family with an autosomal dominant, late-onset spinocerebellar ataxia; the gene is tightly linked to the microsatellite marker D16S397 (LOD score = 5.93 at theta = .00). In addition, we present clinical and electrophysiological data regarding the distinct and previously unreported phenotype consisting of ataxia with the invariant presence of a prominent axonal sensory neuropathy.

The human endothelin-1 gene (EDN1) encoding a peptide with potent vasoactive properties maps distal to HLA on chromosome arm 6p in close linkage to D6S89.

We determined the precise genetic location of the human endothelin-1 gene (EDN1), which encodes a peptide with extremely potent vasoactive properties and is apparently involved in a spectrum of diseases ranging from hypertension to asthma. Analyzing the segregation of a four-allele EDN1 polymorphism in 40 CEPH families including 480 individuals, we detected significant linkage of EDN1 to DNA markers spanning the telomeric half of chromosome arm 6p. EDN1 was closest to the highly polymorphic nucleotide-repeat marker D6S89 at a theta = 0.06 with the highest pairwise LOD score Zmax = 31.2. Subsequent multipoint analysis placed EDN1 at 8 cM distal to D6S89; EDN1 was flanked at its telomeric site at a 13-cM distance by the gene encoding the A subunit of blood clotting factor XIII (F13A1). Furthermore, EDN1 was located at approximately 34-36 cM distal to the HLA region defined by HLA-A, -B, and -DRB1, and 31 cM proximal to the most telomeric marker D6S7. This location of EDN1 on the primary genetic map is strongly supported with odds of 2.7 x 10(12):1 against the next best alternative.

A YAC contig encompassing the recessive Stargardt disease gene (STGD) on chromosome 1p.

Stargardt disease (STGD) and fundus flavimaculatus are infrequent autosomal recessive conditions characterized by a juvenile macular dystrophy and variable degrees of peripheral retinal changes. Linkage analysis performed in 47 STGD/fundus flavimaculatus families demonstrated significant linkage to 13 polymorphic DNA markers on chromosome 1p. The maximum combined two-point lod score was 32.7 (maximum recombination fraction [phi max] = .006) with the polymorphic marker D1S188. Our data demonstrate that STGD and fundus flavimaculatus are the same disorder clinically and genetically and provide further evidence for genetic homogeneity of this phenotype. Analysis of recombination events on disease chromosomes placed the STGD gene within a 4-cM interval between markers D1S435 and D1S236. A physical map was constructed of a YAC contig flanking STGD, from markers D1S500 to D1S495, and includes the critical interval delineated by historical recombinants. This contig spans approximately 31 cM, with one gap (3-5 cM) that is outside the 4-cM critical region. Localization of STGD to a single YAC contig will facilitate its positional cloning.

A gene for familial total anomalous pulmonary venous return maps to chromosome 4p13-q12.

Total anomalous pulmonary venous return (TAPVR) is a cyanotic congenital heart defect that, without surgical correction, has a high mortality rate in the first year of life. It usually occurs without a family history and has a low recurrence risk. However, we recently reported a large Utah-Idaho family in which TAPVR segregates as an autosomal dominant trait with decreased penetrance. Linkage mapping with highly polymorphic microsatellite markers localizes the disease locus in this pedigree to the centromeric region of chromosome 4 (maximum lod = 6.51 at theta = .00). Apparent genetic anticipation in the pedigree prompted a search for expanded trinucleotide repeats by using repeat expansion detection. We have found no evidence for a trinucleotide repeat expansion that segregates with TAPVR. A vascular endothelial growth-factor receptor that is thought to have a role in vasculogenesis maps near the pericentric region of chromosome 4 and is a candidate gene for both familial and sporadic cases of TAPVR.

Novel locus for autosomal dominant hereditary spastic paraplegia, on chromosome 8q.

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of disorders characterized by insidiously progressive spastic weakness in the legs. Genetic loci for autosomal dominant HSP exist on chromosomes 2p, 14q, and 15q. These loci are excluded in 45% of autosomal dominant HSP kindreds, indicating the presence of additional loci for autosomal dominant HSP. We analyzed a Caucasian kindred with autosomal dominant HSP and identified tight linkage between the disorder and microsatellite markers on chromosome 8q (maximum two-point LOD score 5.51 at recombination fraction 0). Our results clearly establish the existence of a locus for autosomal dominant HSP on chromosome 8q23-24. Currently this locus spans 6.2 cM between D8S1804 and D8S1774 and includes several potential candidate genes. Identifying this novel HSP locus on chromosome 8q23-24 will facilitate discovery of this HSP gene, improve genetic counseling for families with linkage to this locus, and extend our ability to correlate clinical features with different HSP loci.

Molecular cloning and physical and genetic mapping of a novel human Na+/H+ exchanger (NHE5/SLC9A5) to chromosome 16q22.1.

A human genomic clone for a novel fifth member of the Na+/H+ exchanger (NHE) family, NHE5 (gene symbol SLC9A5), has been isolated and partially sequenced. The deduced amino acid sequence of two exons, containing 154 codons, exhibits 59-73% identity to the other members of the NHE family, with closest similarity to NHE3. Northern blot analysis demonstrated that the NHE5 gene is expressed in brain, testis, spleen, and skeletal muscle. Fluorescence in situ hybridization analysis of a cosmid containing NHE5 to human metaphase chromosomes localized the NHE5 gene to the cytogenetic interval 16q21-q22. A panel of somatic cell hybrids containing various portions of chromosome 16 was used to refine further the placement of NHE5 within band 16q22.1. A polymorphic dinucleotide (GT/CA)n repeat contained in the NHE5 cosmid was identified and developed into a microsatellite PCR marker. This was typed in a subset of the CEPH (Centre d'Etude du Polymorphisme Humain) families to place it on a genetic map of the human genome. Pairwise linkage analysis of this marker showed that it was linked to marker D16S421 with a maximal lod score of 35.21 at a recombination fraction (theta) of 0.000, in complete concordance with its chromosomal localization by physical mapping. Multipoint linkage analysis placed NHE5 between the flanking markers D16S421 and D16S512. The cloning of this new member of the sodium hydrogen exchanger family, its chromosomal localization, and the discovery of a polymorphic marker for it now make it feasible to study the possible involvement of this gene in disorders of Na+/H+ transport.

Linkage of a variant or attenuated form of adenomatous polyposis coli to the adenomatous polyposis coli (APC) locus.

Adenomatous polyps are an intermediate in the pathway to colon carcinoma. An inherited disorder, familial adenomatous polyposis coli (APC), is characterized by hundreds to thousands of adenomatous polyps. A previously reported family had colon cancer associated with a low average but highly heterogenous number of colonic polyps, this phenotype mapped to the APC locus on 5q. Four new families have been ascertained in which the phenotypic pattern was different from classical polyposis but similar to that of the "prototype" kindred reported earlier. By multilocus linkage analysis, the gene responsible for the disease phenotype was mapped, with a high level of confidence, to the APC locus in two of the four families with the attenuated or variant form of polyposis (AAPC); the results for the two remaining kindreds were inconclusive. A combined maximum LOD score of approximately 7.6 at a recombination fraction of 0 was obtained when the results were summed over the four pedigrees with markers closest to the APC locus. The establishment of genetic linkage in such families may point to the APC locus as having a more significant role in inherited predispositions to colorectal cancer than was previously thought.

A gene for distal arthrogryposis type I maps to the pericentromeric region of chromosome 9.

Club foot is one of the most common human congenital malformations. Distal arthrogryposis type I (DA-1) is a frequent cause of dominantly inherited club foot. Performing a genomewide search using short tandem repeat (STR) polymorphisms, we have mapped a DA-1 gene to the pericentromeric region of chromosome 9 in a large kindred. Linkage analysis has generated a positive lod score of 5.90 at theta = 0, with the marker GS-4. Multiple recombinants bracketing the region have been identified. Analysis of an additional family demonstrated no linkage to the same locus, indicating likely locus heterogeneity. Of the autosomal congenital contracture disorders causing positional foot deformities, this is the first to be mapped.