From environmental responses to adaptation: the roles of plant lncRNAs.

As sessile organisms, plants are continuously exposed to heterogeneous and changing environments and constantly need to adapt their growth strategies. They have evolved complex mechanisms to recognize various stress factors, activate appropriate signaling pathways, and respond accordingly by reprogramming the expression of multiple genes at the transcriptional, post-transcriptional, and even epigenome levels to tolerate stressful conditions such as drought, high temperature, nutrient deficiency, and pathogenic interactions. Apart from protein-coding genes, long non-coding RNAs (lncRNAs) have emerged as key players in plant adaptation to environmental stresses. They are transcripts larger than 200 nucleotides without protein-coding potential. Still, they appear to regulate a wide range of processes, including epigenetic modifications and chromatin reorganization, as well as transcriptional and post-transcriptional modulation of gene expression, allowing plant adaptation to various environmental stresses. LncRNAs can positively or negatively modulate stress responses, affecting processes such as hormone signaling, temperature tolerance, and nutrient deficiency adaptation. Moreover, they also seem to play a role in stress memory, wherein prior exposure to mild stress enhances plant ability to adapt to subsequent stressful conditions. In this review, we summarize the contribution of lncRNAs in plant adaptation to biotic and abiotic stresses, as well as stress memory. The complex evolutionary conservation of lncRNAs is also discussed and provides insights into future research directions in this field.

The Arabidopsis lncRNA ASCO modulates the transcriptome through interaction with splicing factors.

Alternative splicing (AS) is a major source of transcriptome diversity. Long noncoding RNAs (lncRNAs) have emerged as regulators of AS through different molecular mechanisms. In Arabidopsis thaliana, the AS regulators NSRs interact with the ALTERNATIVE SPLICING COMPETITOR (ASCO) lncRNA. Here, we analyze the effect of the knock-down and overexpression of ASCO at the genome-wide level and find a large number of deregulated and differentially spliced genes related to flagellin responses and biotic stress. In agreement, ASCO-silenced plants are more sensitive to flagellin. However, only a minor subset of deregulated genes overlaps with the AS defects of the nsra/b double mutant, suggesting an alternative way of action for ASCO. Using biotin-labeled oligonucleotides for RNA-mediated ribonucleoprotein purification, we show that ASCO binds to the highly conserved spliceosome component PRP8a. ASCO overaccumulation impairs the recognition of specific flagellin-related transcripts by PRP8a. We further show that ASCO also binds to another spliceosome component, SmD1b, indicating that it interacts with multiple splicing factors. Hence, lncRNAs may integrate a dynamic network including spliceosome core proteins, to modulate transcriptome reprogramming in eukaryotes.

A family-based genome-wide association study reveals an association of spondyloarthritis with MAPK14.

OBJECTIVE: More than 40 loci have been associated with ankylosing spondylitis (AS), but less is known about genetic associations in spondyloarthritis (SpA) as a whole. We conducted a family-based genome-wide association study (GWAS) to identify new non-major histocompatibility complex (MHC) genetic factors associated with SpA. METHODS: 906 subjects from 156 French multiplex families, including 438 with SpA, were genotyped using Affymetrix 250K microarrays. Association was tested with Unphased. The best-associated non-MHC single nucleotide polymorphisms (SNPs) were then genotyped in two independent familial cohorts (including 215 French and 294 North American patients with SpA, respectively) to replicate associations. RESULTS: 43 non-MHC SNPs yielded an association signal with SpA in the discovery cohort (p<1×10-4). In the extension studies, association was replicated at a nominal p value of p<0.05 for 16 SNPs in the second cohort and for three SNPs in the third cohort. Combined analysis identified an association close to genome-wide significance between rs7761118, an intronic SNP of MAPK14, and SpA (p=3.5×10-7). Such association appeared to be independent of HLA-B27. CONCLUSIONS: We report here for the first time a family-based GWAS study on SpA and identified an associated polymorphism near MAPK14. Further analyses are needed to better understand the functional basis of this genetic association.

Whole-genome single nucleotide polymorphism-based linkage analysis in spondyloarthritis multiplex families reveals a new susceptibility locus in 13q13.

OBJECTIVE: Spondyloarthritis (SpA) is a chronic inflammatory disorder with high heritability but with complex genetics. Apart from HLA-B27, most of the underlying genetic components remain to be identified. We conducted a whole-genome high-density non-parametric linkage analysis to identify new genetic factors of susceptibility to SpA. METHODS: 914 subjects including 462 with SpA from 143 multiplex families were genotyped using Affymetrix 250K microarrays. After quality control, 189 368 single nucleotide polymorphisms (SNPs) were kept for further analyses. Both non-parametric and parametric linkage analyses were performed using Merlin software. Association was tested with Unphased. RESULTS: Non-parametric linkage analysis identified two regions significantly linked to SpA: the major histocompatibility complex (LODmax=24.77) and a new 13q13 locus (LODmax=5.03). Additionally, eight loci achieved suggestive LOD scores, including the previously identified SPA2 locus at 9q33 (LODmax=3.51). Parametric analysis supported a codominant model in 13q13 with a maximum heterogeneity LOD, 'HLOD' score of 3.084 (α=0.28). Identification of meiotic recombination events around the 13q13 linkage peak in affected subjects from the 43 best-linked families allowed us to map the disease interval between 38.753 and 40.040 Mb. Family-based association analysis of the SNPs inside this interval in the best-linked families identified a SNP near FREM2 (rs1945502) which reached a p value close to statistical significance (corrected p=0.08). CONCLUSION: We report here for the first time a significant linkage between 13q13 and SpA. Identification of susceptibility factor inside this chromosomal region through targeted sequencing in linked families is underway.

Dual function of MIPS1 as a metabolic enzyme and transcriptional regulator.

Because regulation of its activity is instrumental either to support cell proliferation and growth or to promote cell death, the universal myo-inositol phosphate synthase (MIPS), responsible for myo-inositol biosynthesis, is a critical enzyme of primary metabolism. Surprisingly, we found this enzyme to be imported in the nucleus and to interact with the histone methyltransferases ATXR5 and ATXR6, raising the question of whether MIPS1 has a function in transcriptional regulation. Here, we demonstrate that MIPS1 binds directly to its promoter to stimulate its own expression by locally inhibiting the spreading of ATXR5/6-dependent heterochromatin marks coming from a transposable element. Furthermore, on activation of pathogen response, MIPS1 expression is reduced epigenetically, providing evidence for a complex regulatory mechanism acting at the transcriptional level. Thus, in plants, MIPS1 appears to have evolved as a protein that connects cellular metabolism, pathogen response and chromatin remodeling.

Mutations in GLIS3 are responsible for a rare syndrome with neonatal diabetes mellitus and congenital hypothyroidism.

We recently described a new neonatal diabetes syndrome associated with congenital hypothyroidism, congenital glaucoma, hepatic fibrosis and polycystic kidneys. Here, we show that this syndrome results from mutations in GLIS3, encoding GLI similar 3, a recently identified transcription factor. In the original family, we identified a frameshift mutation predicted to result in a truncated protein. In two other families with an incomplete syndrome, we found that affected individuals harbor deletions affecting the 11 or 12 5'-most exons of the gene. The absence of a major transcript in the pancreas and thyroid (deletions from both families) and an eye-specific transcript (deletion from one family), together with residual expression of some GLIS3 transcripts, seems to explain the incomplete clinical manifestations in these individuals. GLIS3 is expressed in the pancreas from early developmental stages, with greater expression in beta cells than in other pancreatic tissues. These results demonstrate a major role for GLIS3 in the development of pancreatic beta cells and the thyroid, eye, liver and kidney.

Multiple functions of Kip-related protein5 connect endoreduplication and cell elongation.

Despite considerable progress in our knowledge regarding the cell cycle inhibitor of the Kip-related protein (KRP) family in plants, less is known about the coordination of endoreduplication and cell differentiation. In animals, the role of cyclin-dependent kinase (CDK) inhibitors as multifunctional factors coordinating cell cycle regulation and cell differentiation is well documented and involves not only the inhibition of CDK/cyclin complexes but also other mechanisms, among them the regulation of transcription. Interestingly, several plant KRPs have a punctuated distribution in the nucleus, suggesting that they are associated with heterochromatin. Here, one of these chromatin-bound KRPs, KRP5, has been studied in Arabidopsis (Arabidopsis thaliana). KRP5 is expressed in endoreduplicating cells, and loss of KRP5 function decreases endoreduplication, indicating that KRP5 is a positive regulator of endoreduplication. This regulation relies on several mechanisms: in addition to its role in cyclin/CDK kinase inhibition previously described, chromatin immunoprecipitation sequencing data combined with transcript quantification provide evidence that KRP5 regulates the transcription of genes involved in cell wall organization. Furthermore, KRP5 overexpression increases chromocenter decondensation and endoreduplication in the Arabidopsis trithorax-related protein5 (atxr5) atxr6 double mutant, which is deficient for the deposition of heterochromatin marks. Hence, KRP5 could bind chromatin to coordinately control endoreduplication and chromatin structure and allow the expression of genes required for cell elongation.

TFAP2B -dietary protein and glycemic index interactions and weight maintenance after weight loss in the DiOGenes trial.

BACKGROUND: TFAP2B rs987237 is associated with obesity and has shown interaction with the dietary fat-to-carbohydrate ratio, which has an effect on weight loss. We investigated interactions between rs987237 and protein-to-carbohydrate ratio or glycemic index (GI) in relation to weight maintenance after weight loss. METHODS: This study included 742 obese individuals from 8 European countries who participated in the Diet, Obesity, and Genes (DiOGenes) trial, lost ≥ 8% of their initial body weight during an 8-week low-calorie diet and were randomized to one of 5 ad libitum diets with a fixed energy percentage from fat: either low-protein/low-GI, low-protein/high-GI, high-protein/low-GI, or high-protein/high-GI diets, or a control diet for a 6-month weight maintenance period. Using linear regression analyses and additive genetic models, we investigated main and dietary interaction effects of TFAP2B rs987237 in relation to weight maintenance. RESULTS: In total, 468 completers of the trial were genotyped for rs987237. High-protein diets were beneficial for weight maintenance in the AA genotype group (67% of participants), but in the AG and GG groups no differences were observed for low- or high-protein diets. On the high-protein diet, carriers of the obesity risk allele (G allele) regained 1.84 kg (95% CI: 0.02; 3.67, p = 0.047) more body weight per risk allele than individuals on a low-protein diet. There was no interaction effect between rs987237 and GI on weight maintenance. CONCLUSION: TFAP2B rs987237 and dietary protein/carbohydrate interacted to modify weight maintenance. Considering the carbohydrate proportion of the diet, the interaction was different from the previously reported rs987237-fat-to-carbohydrate ratio interaction for weight loss. Thus, TFAP2B-macronutrient interactions might diverge depending on the nutritional state.

Mutations in DHDPSL are responsible for primary hyperoxaluria type III.

Primary hyperoxaluria (PH) is an autosomal-recessive disorder of endogenous oxalate synthesis characterized by accumulation of calcium oxalate primarily in the kidney. Deficiencies of alanine-glyoxylate aminotransferase (AGT) or glyoxylate reductase (GRHPR) are the two known causes of the disease (PH I and II, respectively). To determine the etiology of an as yet uncharacterized type of PH, we selected a cohort of 15 non-PH I/PH II patients from eight unrelated families with calcium oxalate nephrolithiasis for high-density SNP microarray analysis. We determined that mutations in an uncharacterized gene, DHDPSL, on chromosome 10 cause a third type of PH (PH III). To overcome the difficulties in data analysis attributed to a state of compound heterozygosity, we developed a strategy of "heterozygosity mapping"-a search for long heterozygous patterns unique to all patients in a given family and overlapping between families, followed by reconstruction of haplotypes. This approach enabled us to determine an allelic fragment shared by all patients of Ashkenazi Jewish descent and bearing a 3 bp deletion in DHDPSL. Overall, six mutations were detected: four missense mutations, one in-frame deletion, and one splice-site mutation. Our assumption is that DHDPSL is the gene encoding 4-hydroxy-2-oxoglutarate aldolase, catalyzing the final step in the metabolic pathway of hydroxyproline.

The function of the RNA-binding protein TEL1 in moss reveals ancient regulatory mechanisms of shoot development.

The shoot represents the basic body plan in land plants. It consists of a repeated structure composed of stems and leaves. Whereas vascular plants generate a shoot in their diploid phase, non-vascular plants such as mosses form a shoot (called the gametophore) in their haploid generation. The evolution of regulatory mechanisms or genetic networks used in the development of these two kinds of shoots is unclear. TERMINAL EAR1-like genes have been involved in diploid shoot development in vascular plants. Here, we show that disruption of PpTEL1 from the moss Physcomitrella patens, causes reduced protonema growth and gametophore initiation, as well as defects in gametophore development. Leafy shoots formed on ΔTEL1 mutants exhibit shorter stems with more leaves per shoot, suggesting an accelerated leaf initiation (shortened plastochron), a phenotype shared with the Poaceae vascular plants TE1 and PLA2/LHD2 mutants. Moreover, the positive correlation between plastochron length and leaf size observed in ΔTEL1 mutants suggests a conserved compensatory mechanism correlating leaf growth and leaf initiation rate that would minimize overall changes in plant biomass. The RNA-binding protein encoded by PpTEL1 contains two N-terminus RNA-recognition motifs, and a third C-terminus non-canonical RRM, specific to TEL proteins. Removal of the PpTEL1 C-terminus (including this third RRM) or only 16-18 amino acids within it seriously impairs PpTEL1 function, suggesting a critical role for this third RRM. These results show a conserved function of the RNA-binding PpTEL1 protein in the regulation of shoot development, from early ancestors to vascular plants, that depends on the third TEL-specific RRM.

Gene duplication within the Green Lineage: the case of TEL genes.

Recent years have witnessed a breathtaking increase in the availability of genome sequence data, providing evidence of the highly duplicate nature of eukaryotic genomes. Plants are exceptional among eukaryotic organisms in that duplicate loci compose a large fraction of their genomes, partly because of the frequent occurrence of polyploidy (or whole-genome duplication) events. Tandem gene duplication and transposition have also contributed to the large number of duplicated genes in plant genomes. Evolutionary analyses allowed the dynamics of duplicate gene evolution to be studied and several models were proposed. It seems that, over time, many duplicated genes were lost and some of those that were retained gained new functions and/or expression patterns (neofunctionalization) or subdivided their functions and/or expression patterns between them (subfunctionalization). Recent studies have provided examples of genes that originated by duplication with successive diversification within plants. In this review, we focused on the TEL (TERMINAL EAR1-like) genes to illustrate such mechanisms. Emerged from the mei2 gene family, these TEL genes are likely to be land plant-specific. Phylogenetic analyses revealed one or two TEL copies per diploid genome. TEL gene degeneration and loss in several Angiosperm species such as in poplar and maize seem to have occurred. In Arabidopsis thaliana, whose genome experienced at least three polyploidy events followed by massive gene loss and genomic reorganization, two TEL genes were retained and two new shorter TEL-like (MCT) genes emerged. Molecular and expression analyses suggest for these genes sub- and neofunctionalization events, but confirmation will come from their functional characterization.

Comprehensive linkage and association analyses identify haplotype, near to the TNFSF15 gene, significantly associated with spondyloarthritis.

Spondyloarthritis (SpA) is a chronic inflammatory disorder with a strong genetic predisposition dominated by the role of HLA-B27. However, the contribution of other genes to the disease susceptibility has been clearly demonstrated. We previously reported significant evidence of linkage of SpA to chromosome 9q31-34. The current study aimed to characterize this locus, named SPA2. First, we performed a fine linkage mapping of SPA2 (24 cM) with 28 microsatellite markers in 149 multiplex families, which allowed us to reduce the area of investigation to an 18 cM (13 Mb) locus delimited by the markers D9S279 and D9S112. Second, we constructed a linkage disequilibrium (LD) map of this region with 1,536 tag single-nucleotide polymorphisms (SNPs) in 136 families (263 patients). The association was assessed using a transmission disequilibrium test. One tag SNP, rs4979459, yielded a significant P-value (4.9 x 10(-5)). Third, we performed an extension association study with rs4979459 and 30 surrounding SNPs in LD with it, in 287 families (668 patients), and in a sample of 139 cases and 163 controls. Strong association was observed in both familial and case/control datasets for several SNPs. In the replication study, carried with 8 SNPs in an independent sample of 232 cases and 149 controls, one SNP, rs6478105, yielded a nominal P-value<3 x 10(-2). Pooled case/control study (371 cases and 312 controls) as well as combined analysis of extension and replication data showed very significant association (P<5 x 10(-4)) for 6 of the 8 latter markers (rs7849556, rs10817669, rs10759734, rs6478105, rs10982396, and rs10733612). Finally, haplotype association investigations identified a strongly associated haplotype (P<8.8 x 10(-5)) consisting of these 6 SNPs and located in the direct vicinity of the TNFSF15 gene. In conclusion, we have identified within the SPA2 locus a haplotype strongly associated with predisposition to SpA which is located near to TNFSF15, one of the major candidate genes in this region.

Impact of pre- and post-variant filtration strategies on imputation.

Quality control (QC) methods for genome-wide association studies and fine mapping are commonly used for imputation, however they result in loss of many single nucleotide polymorphisms (SNPs). To investigate the consequences of filtration on imputation, we studied the direct effects on the number of markers, their allele frequencies, imputation quality scores and post-filtration events. We pre-phrased 1031 genotyped individuals from diverse ethnicities and compared the imputed variants to 1089 NCBI recorded individuals for additional validation. Without QC-based variant pre-filtration, we observed no impairment in the imputation of SNPs that failed QC whereas with pre-filtration there was an overall loss of information. Significant differences between frequencies with and without pre-filtration were found only in the range of very rare (5E-04-1E-03) and rare variants (1E-03-5E-03) (p < 1E-04). Increasing the post-filtration imputation quality score from 0.3 to 0.8 reduced the number of single nucleotide variants (SNVs) < 0.001 2.5 fold with or without QC pre-filtration and halved the number of very rare variants (5E-04). Thus, to maintain confidence and enough SNVs, we propose here a two-step filtering procedure which allows less stringent filtering prior to imputation and post-imputation in order to increase the number of very rare and rare variants compared to conservative filtration methods.

Structure and vascular tissue expression of duplicated TERMINAL EAR1-like paralogues in poplar.

TERMINAL EAR1-like (TEL) genes encode putative RNA-binding proteins only found in land plants. Previous studies suggested that they may regulate tissue and organ initiation in Poaceae. Two TEL genes were identified in both Populus trichocarpa and the hybrid aspen Populus tremula x P. alba, named, respectively, PoptrTEL1-2 and PtaTEL1-2. The analysis of the organisation around the PoptrTEL genes in the P. trichocarpa genome and the estimation of the synonymous substitution rate for PtaTEL1-2 genes indicate that the paralogous link between these two Populus TEL genes probably results from the Salicoid large-scale gene-duplication event. Phylogenetic analyses confirmed their orthology link with the other TEL genes. The expression pattern of both PtaTEL genes appeared to be restricted to the mother cells of the plant body: leaf founder cells, leaf primordia, axillary buds and root differentiating tissues, as well as to mother cells of vascular tissues. Most interestingly, PtaTEL1-2 transcripts were found in differentiating cells of secondary xylem and phloem, but probably not in the cambium itself. Taken together, these results indicate specific expression of the TEL genes in differentiating cells controlling tissue and organ development in Populus (and other Angiosperm species).

European collaborative study of early-onset bipolar disorder: Evidence for genetic heterogeneity on 2q14 according to age at onset.

Bipolar disorder has a genetic component, but the mode of inheritance remains unclear. A previous genome scan conducted in 70 European families led to detect eight regions linked to bipolar disease. Here, we present an investigation of whether the phenotypic heterogeneity of the disorder corresponds to genetic heterogeneity in these regions using additional markers and an extended sample of families. The MLS statistic was used for linkage analyses. The predivided sample test and the maximum likelihood binomial methods were used to test genetic homogeneity between early-onset bipolar type I (cut-off of 22 years) and other types of the disorder (later onset of bipolar type I and early-onset bipolar type II), using a total of 138 independent bipolar-affected sib-pairs. Analysis of the extended sample of families supports linkage in four regions (2q14, 3p14, 16p23, and 20p12) of the eight regions of linkage suggested by our previous genome scan. Heterogeneity testing revealed genetic heterogeneity between early and late-onset bipolar type I in the 2q14 region (P = 0.0001). Only the early form of the bipolar disorder but not the late form appeared to be linked to this region. This region may therefore include a genetic factor either specifically involved in the early-onset bipolar type I or only influencing the age at onset (AAO). Our findings illustrate that stratification according to AAO may be valuable for the identification of genetic vulnerability polymorphisms. © 2010 Wiley-Liss, Inc.

Fine mapping of quantitative trait loci affecting female fertility in dairy cattle on BTA03 using a dense single-nucleotide polymorphism map.

Fertility quantitative trait loci (QTL) are of high interest in dairy cattle since insemination failure has dramatically increased in some breeds such as Holstein. High-throughput SNP analysis and SNP microarrays give the opportunity to genotype many animals for hundreds SNPs per chromosome. In this study, due to these techniques a dense SNP marker map was used to fine map a QTL underlying nonreturn rate measured 90 days after artificial insemination previously detected with a low-density microsatellite marker map. A granddaughter design with 17 Holstein half-sib families (926 offspring) was genotyped for a set of 437 SNPs mapping to BTA3. Linkage analysis was performed by both regression and variance components analysis. An additional analysis combining both linkage analysis and linkage-disequilibrium information was applied. This method first estimated identity-by-descent probabilities among base haplotypes. These probabilities were then used to group the base haplotypes in different clusters. A QTL explaining 14% of the genetic variance was found with high significance (P < 0.001) at position 19 cM with the linkage analysis and four sires were estimated to be heterozygous (P < 0.05). Addition of linkage-disequilibrium information refined the QTL position to a set of narrow peaks. The use of the haplotypes of heterozygous sires offered the possibility to give confidence in some peaks while others could be discarded. Two peaks with high likelihood-ratio test values in the region of which heterozygous sires shared a common haplotype appeared particularly interesting. Despite the fact that the analysis did not fine map the QTL in a unique narrow region, the method proved to be able to handle efficiently and automatically a large amount of information and to refine the QTL position to a small set of narrow intervals. In addition, the QTL identified was confirmed to have a large effect (explaining 13.8% of the genetic variance) on dairy cow fertility as estimated by nonreturn rate at 90 days.

Nuclear Speckle RNA Binding Proteins Remodel Alternative Splicing and the Non-coding Arabidopsis Transcriptome to Regulate a Cross-Talk Between Auxin and Immune Responses.

Nuclear speckle RNA binding proteins (NSRs) act as regulators of alternative splicing (AS) and auxin-regulated developmental processes such as lateral root formation in Arabidopsis thaliana. These proteins were shown to interact with specific alternatively spliced mRNA targets and at least with one structured lncRNA, named Alternative Splicing Competitor RNA. Here, we used genome-wide analysis of RNAseq to monitor the NSR global role on multiple tiers of gene expression, including RNA processing and AS. NSRs affect AS of 100s of genes as well as the abundance of lncRNAs particularly in response to auxin. Among them, the FPA floral regulator displayed alternative polyadenylation and differential expression of antisense COOLAIR lncRNAs in nsra/b mutants. This may explains the early flowering phenotype observed in nsra and nsra/b mutants. GO enrichment analysis of affected lines revealed a novel link of NSRs with the immune response pathway. A RIP-seq approach on an NSRa fusion protein in mutant background identified that lncRNAs are privileged direct targets of NSRs in addition to specific AS mRNAs. The interplay of lncRNAs and AS mRNAs in NSR-containing complexes may control the crosstalk between auxin and the immune response pathway.

Autosomal recessive spastic paraplegia (SPG30) with mild ataxia and sensory neuropathy maps to chromosome 2q37.3.

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterized by progressive spasticity in the lower limbs. Twenty-nine different loci (SPG) have been mapped so far, and 11 responsible genes have been identified. Clinically, one distinguishes between pure and complex HSP forms which are variably associated with numerous combinations of neurological and extra-neurological signs. Less is known about autosomal recessive forms (ARHSP) since the mapped loci have been identified often in single families and account for only a small percentage of patients. We report a new ARHSP locus (SPG30) on chromosome 2q37.3 in a consanguineous family with seven unaffected and four affected members of Algerian origin living in Eastern France with a significant multipoint lod score of 3.8. Ten other families from France (n = 4), Tunisia (n = 2), Algeria (n = 3) and the Czech Republic (n = 1) were not linked to the newly identified locus thus demonstrating further genetic heterogeneity. The phenotype of the linked family consists of spastic paraparesis and peripheral neuropathy associated with slight cerebellar signs confirmed by cerebellar atrophy on one CT scan.

A new phenotype linked to SPG27 and refinement of the critical region on chromosome.

Hereditary spastic paraplegias are genetically and clinically heterogeneous. Twenty-six loci have been identified to date. SPG27 was recently mapped to chromosome 10 in a single family with autosomal recessive hereditary spastic paraplegia (AR-HSP) and a pure phenotype. We describe a Tunisian family with a complicated form of AR-HSP also linked to SPG27. The parents are first cousins and 3 out of their 4 children manifest early onset progressive spastic paraparesis associated with sensorimotor polyneuropathy. In addition, the eldest girl had facial dysmorphism and short stature (-3SD). Two of the three patients were mentally retarded, and one of these also had cerebellar signs. Their ages at onset were 2, 5 and 7 years. A genome-wide scan suggested linkage to SPG27 on the long arm of chromosome 10 with a multipoint lod score of 2.54. In addition, a recombination detected in this family by haplotype reconstruction reduced the SPG27 locus from 25 to 19.6 cM. This is the first clinical description of a complicated form of spastic paraplegia, characterized by great phenotypic variability among the sibs, associated with the SPG27 locus.