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A large family with pure autosomal dominant hereditary spastic paraplegia from southern Italy mapping to chromosome 14q11.2-q24.3.

A large Italian pedigree from southern Italy with autosomal dominant uncomplicated spastic paraplegia is reported. The clinical picture was uniform and characterized by insidiously progressive lower extremity weakness and spasticity. The mean age at onset of symptoms was 8.3 years. Significant linkage to the SPG3 locus on chromosome 14 was detected. The authors also report their search for mutations in a gene located in the region and its exclusion as a candidate for SPG3.

Adult↗

A new locus for coeliac disease mapped to chromosome 15 in a population isolate.

Coeliac disease is a common multifactorial disease with a strong genetic component, which is not entirely explained by the HLA association. Four previous whole-genome screens have produced somewhat inconsistent results suggesting genetic heterogeneity. We attempted to overcome this problem by performing a genome-wide scan in a Finnish sub-population, expected to be more homogeneous than the general population of Finland. The families in our study originate from the northeastern part of Finland, the Koilliskaira region, which has been relatively isolated since its founding in the 16th century. Genealogical studies have confirmed that the families share a common ancestor in the 16th century. Nine families with altogether 23 patients were genotyped for 399 microsatellite markers and the data were analysed with parametric linkage analysis using two dominant and one recessive model. A region on chromosome 15q11-q13 was implicated with a LOD score of 3.14 using a highly penetrant dominant model. Addition of more markers and one more sib-pair increased the LOD score to 3.74. This result gives preliminary evidence for existence of a susceptibility factor in this chromosomal region.

Celiac Disease↗

A new locus for autosomal dominant Charcot-Marie-Tooth disease type 2 (CMT2L) maps to chromosome 12q24.

Charcot-Marie-Tooth disease (CMT) is one of the most common inherited neurological disorders with a prevalence estimated at 1/2500. The axonal form of this disorder is referred to as Charcot-Marie-Tooth type 2 disease (CMT2). Recently, a large Chinese family with CMT2 was found in the Hunan and Hubei provinces of China. The known loci for CMT1A, CMT2D, CMT1B (the same locus is also responsible for CMT2I and CMT2J), CMT2A, CMT2E, and CMT2F were excluded in this family by linkage analysis. A genome-wide screening was then carried out, and the results revealed linkage of CMT2 to a locus at chromosome 12q24. Haplotype construction and analyses localized this novel locus to a 6.8-cM interval between microsatellite markers D12S366 and D12S1611. The maximal two-point LOD score of 6.35 and multipoint LOD score of 8.08 for marker D12S76 at a recombination fraction (theta) of 0 strongly supported linkage to this locus. Thus, CMT2 neuropathy in this family represents a novel genetic entity that we have designated as CMT2L.

Adolescent↗

A new locus (RP31) for autosomal dominant retinitis pigmentosa maps to chromosome 9p.

Retinitis pigmentosa (RP) is a debilitating disease of the retina affecting approximately 1.5 million people worldwide. RP shows remarkable heterogeneity both clinically and genetically, with more than 40 genetic loci implicated, 12 of which account for the autosomal dominant form (adRP) of inheritance. We have recently identified a French Canadian family that presents with early onset adRP. After exclusion of all known loci for adRP, a genome-wide search established firm linkage with a marker from the short arm of chromosome 9 (LOD score of 6.3 at recombination fraction theta=0). The linked region is flanked by markers D9S285 and D9S1874, corresponding to a genetic distance of 31 cM, in the region 9p22-p13.

Age of Onset↗

A locus for familial generalized lentiginosis without systemic involvement maps to chromosome 4q21.1-q22.3.

Generalized lentiginosis (GL) is characterized by widespread lentigines without associated noncutaneous abnormalities. In this study we performed a genome-wide linkage search in a Chinese family with GL and localized the familial GL locus to chromosome 4q21.1-q22.3, with a maximum two-point LOD score of 3.01 for D4S395 and D4S423 at a recombination fraction of 0. Multipoint analysis (maximum LOD score of 5.08 between markers D4S395 and D4S1563) and haplotype construction showed strong evidence of linkage in a region of 20 Mb flanked by markers D4S2915 and D4S1560 on chromosome 4q21.1-q22.3. This is the first report of linkage for GL, and it will provide further insight into the controversy of whether GL is an entity distinct from LEOPARD syndrome.

China↗

A novel locus (RP33) for autosomal dominant retinitis pigmentosa mapping to chromosomal region 2cen-q12.1.

Retinitis pigmentosa (RP) is a heterogeneous group of progressive degenerative disorders of the retina with a strong genetic component. Here, we report the clinical and genetic findings in a Chinese family in which autosomal dominant RP (adRP) was inherited by 13 affected members in four generations. Using a genome-wide linkage screening approach, a novel disease locus (RP33) was assigned to the long arm of chromosome 2. A maximum multi-point LOD score of 4.69 was reached at marker D2S2222 in 2q11.2. Meiotic recombination events in affected members placed RP33 in a 15.5 cM region between D2S329 and D2S2229. From meiotic recombinations in two unaffected members RP33 was further refined to a 4.8 cM (9.5 Mb) interval flanked by D2S2159 and D2S1343 in chromosomal region 2cen-q12.1. No disease-associated mutations were detected in the candidate genes SEMA4C, CNGA3 or HNK1ST from within the region. MERTK, a known disease gene for autosomal recessive RP located close to RP33 was similarly excluded. Clinically, the family presented relatively late onset of night blindness, gradually decreased visual acuity, progressive loss of peripheral visual field and typical RP fundus changes in the mid-periphery of the retina. In conclusion, a novel locus for adRP has been assigned to chromosomal region 2cen-q12.1, which in the present kindred was associated with a relatively late onset form of the disease.

Chromosome Mapping↗

Hereditary neuralgic amyotrophy: evidence for genetic homogeneity and mapping to chromosome 17q25.

Hereditary neuralgic amyotrophy (HNA) is a rare autosomal dominant disorder on chromosome 17q, associated with recurrent, episodic, painful brachial plexus neuropathy. Dysmorphic features, including hypotelorism, long nasal bridge and facial asymmetry, are frequently associated with HNA. To assess genetic homogeneity, determine the cytogenetic location, and identify flanking markers for the HNA locus, six pedigrees were studied with multiple DNA markers from distal chromosome 17q. The results in all pedigrees supported linkage of the HNA locus to chromosome 17. A maximum combined lod score (Z = 10.94, theta = 0.05) was obtained with marker D17S939 and the maximum multipoint lod score was 22.768 in the interval defined by D17S802-D17S939. An analysis of crossovers placed the HNA locus within an approximate 4.0-cM interval flanked by D17S1603 and D17S802. Analysis of DNA from a human/mouse somatic cell hybrid with linked markers suggests that band 17q25 harbors the HNA locus. These results support genetic homogeneity within HNA and define a specific interval and a precise cytogenetic location in chromosome 17q25 for this disorder.

Brachial Plexus↗

A novel locus for parietal foramina maps to chromosome 4q21-q23.

Parietal foramina [PFM], inherited usually in an autosomal dominant mode, is an extremely rare developmental defect characterized by a symmetrical, oval hole in the parietal bone. It can be present as either an isolated or a syndromic feature. PFM types 1 and 2 (PFM1 and PFM2) have been found to be caused by mutations in the MSX2 and ALX4 genes, located to chromosomes 5 and 11, respectively. After exclusion of both the above loci in a large Chinese pedigree with autosomal dominant PFM, a genome-wide search revealed a linkage of the PFM to markers at the 4q21-q23 region. The maximum LOD score from two-point linkage analysis is 3.87 for marker D4S2961. Analysis of co-segregated haplotype localized the region to a 20-cM interval that flanks D4S392 and D4S2945. Therefore, we concluded that the PFM in the family is a new PFM locus. Although three genes, BMPR1B, PP1 and IBSP, are located to 4q21-q25 and their functions are related to bone morphogenesis, no mutations were identified by sequencing analysis of their exons.

Chromosome Mapping↗

A novel locus of coralliform cataract mapped to chromosome 2p24-pter.

Congenital cataract is a common major abnormality of the eye, which can result in significant visual impairment or blindness in childhood. In this work, we studied four generations of a Chinese family that exhibited autosomal dominant coralliform cataract but no other ocular or systemic abnormalities. Members of the family were firstly genotyped with microsatellite markers at loci associated with congenital cataract on the reported regions of chromosomes 1, 2, 3, 10, 11, 12, 13, 15, 16, 17, 20, 21, and 22, but negative LOD scores were obtained. Following exclusion of these loci, a genome-wide scan was performed, and significant evidence of linkage was obtained for marker D2S2211 (Z = 2.69, theta = 0.00). In multipoint analysis, a maximum LOD score 4.87 (theta = 0.00) was reached between markers D2S2211 and D2S2164. Haplotype data indicated a coralliform cataract disease gene in a 26-cM interval at a novel disease locus 2p24-pter between D2S297 and D2S2268. No genes related to cataract in this region have been reported so far.

Cataract↗

The gene encoding human 2-oxoglutarate dehydrogenase: structural organization and mapping to chromosome 7p13-p14.

Genomic clones covering the entire sequence of the gene encoding human 2-oxoglutarate dehydrogenase (OGDH) were isolated by screening leukocyte and placenta genomic libraries with radio- and digoxigenin (DIG)-labeled human OGDH cDNAs. The human OGDH gene contains 22 exons spanning approx. 85 kb. All exon/intron splice junctions follow the GT/AG rule. The results of primer extension analysis imply that the OGDH transcription start point is a thymine residue 55 bp upstream from the ATG start codon. The 5'-flanking region of OGDH lacked canonical TATA or CAAT boxes. Using DNAs from human x rodent somatic cell hybrids that segregate human chromosomes in conjunction with fluorescence in situ hybridization, human OGDH was assigned to chromosome arm 7p, an area that corresponds to the boundary between bands 7p13 and 7p14.

Amino Acid Sequence↗

The alpha subunit of cytochrome b-245 mapped to chromosome 16.

The chromosomal location of the alpha subunit (23-kDa protein) of human cytochrome b-245 was analyzed by Southern blot hybridization using DNA isolated from a panel of 12 independent human-rodent somatic cell hybrids. The results indicate that this protein is encoded at a single locus on chromosome 16.

Animals↗

The human platelet-activating factor receptor gene (PTAFR) contains no introns and maps to chromosome 1.

Platelet-activating factor (PAF), a phospholipid, exhibits a variety of potent inflammatory bioactivities that are mediated by a specific cell surface receptor. The gene for the human PAF receptor (PTAFR) has been isolated by hybridization with a guinea pig probe. The coding sequence contains no intervening sequences. The encoded protein is highly homologous to the guinea pig PAF receptor (82% identity) and contains seven putative transmembrane domains. The PAF receptor therefore appears to be a member of the G protein coupled family of receptors and exhibits significant similarity to many members of the family. Analysis of somatic cell hybrids suggests that the PAF receptor is encoded by a single gene on human chromosome 1.

Amino Acid Sequence↗

cDNA cloning and characterization of the human THRAP2 gene which maps to chromosome 12q24, and its mouse ortholog Thrap2.

Characterization of a balanced t(2;12)(q37;q24) translocation in a patient with suspicion of Noonan syndrome revealed that the chromosome 12 breakpoint lies in the vicinity of a novel human gene, thyroid hormone receptor-associated protein 2 (THRAP2). We therefore characterized this gene and its mouse counterpart in more detail. Human and mouse THRAP2/Thrap2 span a genomic region of about 310 and >170 kilobases (kb), and both contain 31 exons. Corresponding transcripts are approximately 9.5 kb long. Their open reading frames code for proteins of 2210 and 2203 amino acids, which are 93% identical. By northern blot analysis, human and mouse THRAP2/Thrap2 genes showed ubiquitous expression. Transcripts were most abundant in human skeletal muscle and in mouse heart. THRAP2 protein is 56% identical to human TRAP240, which belongs to the thyroid hormone receptor associated protein (TRAP) complex and is evolutionary conserved up to yeast. This complex is involved in transcriptional regulation and is believed to serve as adapting interface between regulatory proteins bound to specific DNA sequences and RNA polymerase II.

Adaptor Proteins, Signal Transducing↗