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Recessive lethal amber suppressors in yeast.

Recessive lethal amber suppressor mutations have been isolated in a diploid strain of Saccharomyces cerevisiae. Diploids carrying these suppressors upon sporulation yield asci with only two live spores, both lacking the suppressor. At least two classes of recessive lethal suppressors exist. Aneuploid strains carrying one wild type and one suppressor locus have been isolated and used in mapping studies; one suppressor maps on chromosome III, the other does not.

Aneuploidy↗

Complementation analysis of methyl methane-sulfonate-induced recessive lethal mutations in the zeste-white region of the X chromosome of Drosophila melanogaster.

Recessive lethan mutations in the 3A1 to 3C2 region of the X-chromosome of Drosophila melanogaster were detected in 113 of 33,544 sperm treated by feeding 5 mM methyl methanesulfonate in 1% sucrose for 22 hours. Seven of the 113 lethans were sterile, leaving 106 for analysis by complementation tests. With only one exception, these mutants were found to have lesions restricted to single loci. One of these single-site mutations was in qt, 2 in tko, 18 in zw-1, 12 in zw-8, 6 in zw-4, 3 in zw-10, 3 in zw-13, 21 in zw-2, 7 in zw-3, 5 in zw-6, 6 in zw-12, 1 in zw-7, 12 in zw-5, 5 in zw-11, and 3 in zw-9. One of the lethals, m69, was non-complementary to two adjacent loci, zw-2 and zw-3, possible indicating a deletion encompassing two loci. The results confirm that there are at least 15 recessive lethal loci in the region and are consistent with the hypothesis of LIM and SYNDER (1968 and 1974) that inability of monofunctional alkylating chemicals to induce deletion associated mutations is a characteristic of the compounds.

Animals↗

The cytogenetics of a recessive visible mutant associated with a deficiency adjacent to the notch locus in Drosophila melanogaster.

The recessive visible faswb allele in Drosophila is an interband deletion between salivary band 3C5, 6 and 7. Heterozygosity for the deletion does not suppress recombination between faswb and mutant sites at Notch adjacent to it.--Df(1)w67k30, deficient for salivary bands 3C2 to 6, is the left of faswb. By crossing over within the homologous bit of interband retained in w67k30 and faswb, the two deficiencies can be linked. Cytologically, 3C7, "fused" to 3C5,6 in faswb, becomes "fused" to 3C1 when the two are coupled. In the double deletion, the recessive visible phenotype of the faswb "allele* is suppressed. Both w67k30 and faswb can be recovered by uncoupling the two deficiencies.--The data suggest that the mutant faswb does not represent a lesion at Notch; the entire gene or locus seems to be present. The interband deletion in faswb has secondarily moved an intact Notch locus to a foreign environment that interferes with its normal function. When faswb is linked to w67k30, the interference is eliminated and normal Notch functions resume.--The position of Notch on the salivary gland chromosome is reviewed in relation to the information obtained in these experiments.

Animals↗

The action of the notchlocus in Drosophila melanogaster. II. Biochemical effects of recessive lethals on mitochondrial enzymes.

We show that six mapped recessive lethal point mutations of the Notch locus affect mitochondrial enzyme activities: NADH oxidase, NADH dehydrogenase, succinate dehydrogenase and alpha-glycerophosphate dehydrogenase. The mutant N264-40, which has the same morphological and embryological effects as the Notch8 deletion, demonstrates the same biochemical effects and dosage relations as Notch8. The other five mapped recessive lethals also affect four enzymic activities. They show specific patterns of activity that depend in several cases on the wild-type chromosome in the heterozygous females. That effect occurs with mutants located in the extreme right part of the Notch locus where some mutations, according to other authors, show temperature-sensitive expression.

Animals↗

Recessive alleles found at R and C loci in maize stocks showing aberrant ratio at the A locus.

Corn stocks showing virus-induced aberrant ratio (AR) at the "A" locus were found to have recessive alleles at the R and/or C loci. Since by the known pedigree these loci should be homozygous dominant, the results suggest an inactivation of maize genes by a mechanism as yet unknown. The presence of recessive alleles at these additional loci can explain the segregation ratios obtained in these particular stocks.

Alleles↗

A mutation in GJB3 is associated with recessive erythrokeratodermia variabilis (EKV) and leads to defective trafficking of the connexin 31 protein.

Erythrokeratodermia variabilis (EKV) is a skin disorder characterized by variable (transient) erythemas and fixed keratosis. The disorder maps to chromosome 1p34-35, a location that contains the GJB3 gene encoding the gap junction protein connexin 31. Until now, only heterozygote mutations in the form of dominant inheritance have been described in this gene associated with EKV. We report here a homozygote mutation in the connexin 31 gene, found in a family that shows recessive inheritance of the disorder, thus providing the first molecular support for a recessive variant of EKV. The entire GJB3 coding sequence was scanned for mutations by sequencing. We detected a T-->C transition at position 101 of the coding sequence, which replaces a leucine with a proline at residue 34 of the protein (L34P). Evolutionary analysis shows that this mutation is located at a highly conserved region of connexin in the first putative transmembrane helix (TMH). In transfected keratinocytes, L34P connexin 31 had a cytoplasmic distribution, suggesting that the mutant form of this protein will not form normal gap junctions between adjacent cells. The change of leucine to proline is likely to alter the structure of the first TMH of connexin by inducing a kink, thus influencing connexon structure and function.

Amino Acid Sequence↗

Evidence for recessive as well as dominant forms of startle disease (hyperekplexia) caused by mutations in the alpha 1 subunit of the inhibitory glycine receptor.

Startle disease, or hyperekplexia, is characterized by an exaggerated startle reflex and neonatal hypertonia. An autosomal dominant form of the disorder is associated with mutations in the same codon of the alpha 1 subunit of the inhibitory glycine receptor (GLRA 1) resulting in the substitution of an uncharged amino acid for Arg271 in the mature protein. However, recessive transmission is seen in the mouse mutant spasmodic which resembles startle disease phenotypically and is also associated with mutations in Glra 1. We have confirmed the finding of Arg271 mutations in individuals with startle disease in a UK family showing autosomal dominant transmission. In addition we describe an apparently sporadic case, the offspring of a consanguineous mating, who is homozygous for a novel mutation (T1112A) in GLRA 1, which results in the substitution of asparagine for isoleucine at position 244 of the mature protein. This suggests that human startle disease can display recessive as well as dominant inheritance resulting from different mutations in GLRA 1.

Adult↗

A gene responsible for a dominant form of neurosensory non-syndromic deafness maps to the NSRD1 recessive deafness gene interval.

The first localization of a gene responsible for autosomal, neurosensory, recessive deafness recently assigned NSRD1 to the centromeric region of human chromosome 13. We now report on a dominant form of neurosensory deafness found in a family of French origin. The deafness is moderate to severe, has a prelingual onset and affects predominantly the high frequencies. The gene responsible for this form of deafness was found by linkage analysis to map to the same region of chromosome 13 as NSRD1. A multipoint analysis gave a maximum lod score of 4.66 with a most likely location close to locus D13S175. This suggests that different mutations in NSRD1 may cause both dominant and recessive neurosensory deafness.

Centromere↗

Mapping a gene (SRN1) to chromosome 1q25-q31 in idiopathic nephrotic syndrome confirms a distinct entity of autosomal recessive nephrosis.

Idiopathic nephrotic syndrome (INS) in childhood is characterized by massive proteinuria and minimal glomerular changes. Most patients with INS respond to steroid therapy. INS is generally regarded as a sporadic disease with favorable outcome. We investigated a distinct subgroup of nephrosis--the familial form of steroid resistant INS (SRN). These patients always progress to end-stage renal failure within a few years and show absence of recurrence of the disease after renal transplantation. The occurrence of the disorder in siblings and the high incidence of inbreeding in these families made an autosomal recessive mode of inheritance very likely. We performed whole genome linkage analysis in nine multiplex families of European or Northern African origin. Our results allowed us to assign a disease locus (SRN1) to a defined chromosomal region on 1q25-1q31, thus confirming the existence of a distinct entity of autosomal recessive nephrosis. Exclusion of linkage to the entire region in one family proves genetic heterogeneity.

Chromosome Mapping↗

A common missense mutation in the adhalin gene in three unrelated Brazilian families with a relatively mild form of autosomal recessive limb-girdle muscular dystrophy.

Autosomal recessive limb-girdle muscular dystrophies (AR LGMD) represent a heterogeneous group of diseases with a wide spectrum of clinical variability, classified phenotypically into two main groups, the most severe forms (Duchenne-like muscular dystrophy, DLMD, or severe childhood autosomal recessive muscular dystrophy, SCARMD) and the milder forms. Four genes causing AR LGMD have been mapped: the 15q (LGMD2a), the 2p (LGMD2b), the 13q locus (LGMD2c) and the adhalin gene on chromosome 17q (LGMD2d). In the present report we have performed linkage analysis with 17q markers in three mild AR LGMD and in four DLMD families with adhalin deficiency and unlinked to 2p, 15q or 13q genes. Linkage was observed only among the mild cases. Patients from these three 17q-linked families showed near or total deficiency of adhalin in muscle biopsies. An identical missense mutation was identified in all three 17q-linked unrelated families. These results indicate that AR LGMD with a mild phenotype is caused by mutations in the adhalin gene. In addition, they demonstrate that there is at least one other locus for DLMD associated with adhalin deficiency.

Base Sequence↗

Consanguineous nuclear families used to identify a new locus for recessive non-syndromic hearing loss on 14q.

Hearing impairment is inherited most frequently as an autosomal recessive isolated clinical finding (non-syndromic hearing loss, NSHL). Extreme heterogeneity and phenotypic variability in the audiometric profile preclude pooling of affected families and severely hamper gene mapping by conventional linkage analysis. However, in instances of consanguinity, homozygosity mapping can be used to identify disease loci in small nuclear families. This report demonstrates the power of this technique by identifying a locus for recessive NSHL on 14q (DFNB4).

Chromosome Mapping↗

Autosomal recessive non-syndromic deafness locus (DFNB8) maps on chromosome 21q22 in a large consanguineous kindred from Pakistan.

Autosomal recessive childhood-onset non-syndromic deafness is one of the most frequent forms of inherited hearing impairment. Recently five different chromosomal regions, 7q31, 11q13.5, 13q12, 14q and the pericentromeric region of chromosome 17, have been shown to harbour disease loci for this type of neurosensory deafness. We have studied a large family from Pakistan, containing several consanguineous marriages and segregating for a recessive non-syndromic childhood-onset deafness. Linkage analysis mapped the disease locus (DFNB8) on the distal long arm of chromosome 21, most likely between D21S212 and D21S1225 with the highest lod score of 7.31 at theta = 0.00 for D21S1575 on 21q22.3.

Adolescent↗

Crigler-Najjar syndrome type II is inherited both as a dominant and as a recessive trait.

Crigler-Najjar syndrome type II (CN-II) is caused by a severely reduced hepatic activity of bilirubin UDP-glucuronosyltransferase (UGT). Recently, by the analysis of the genetic background of CN-II patients, it has been clarified that the patients carry homozygous missense mutations or nonsense plus missense mutations on the gene for UGT, and CN-II was inherited as an autosomal recessive trait. We encountered a new case which had a nonsense mutation caused by a single nucleotide substitution on one allele. This indicates that CN-II is also inherited as a dominant trait as well as a recessive trait. Expression study in vitro strongly suggests that the disease in this case is caused by a dominant negative mutation by forming a heterologous subunit structure.

Amino Acid Sequence↗

Linkage analysis in autosomal recessive limb-girdle muscular dystrophy (AR LGMD) maps a sixth form to 5q33-34 (LGMD2F) and indicates that there is at least one more subtype of AR LGMD.

Limb-girdle muscular dystrophies (LGMDs) represent a clinically heterogeneous group of genetic diseases characterised by progressive weakness of the pelvic and shoulder girdle muscles. An autosomal dominant form (LGMD1A) has been mapped at 5q22.3-31.3, while five genes responsible for the autosomal recessive forms were mapped respectively at: 15q15.1 (LGMD2A), 2p12-p16 (LGMD2B), 13q12 (LGMD2C), 17q12-q21.33 (LGMD2D) and 4q12 (LGMD2E). Among 17 autosomal recessive (AR) LGMD Brazilian families with at least three affected sibs, we were able to exclude four families (one mild and three severe) from all these five known loci as well as from the dystroglycan and syntrophin genes. Therefore, we have performed a genome-wide search in two of the severely affected families, which are alpha-sarcoglycan negative. We demonstrate linkage of these two Duchenne muscular dystrophy-like families to 5q33-34, and propose to classify them as LGMD2F. In addition, linkage analysis in the other two genealogies that are alpha-sarcoglycan positive suggests that there is at least one other gene which causes AR LGMD.

Chromosome Mapping↗

Localization of a gene responsible for autosomal recessive demyelinating neuropathy with focally folded myelin sheaths to chromosome 11q23 by homozygosity mapping and haplotype sharing.

Hereditary motor and sensory neuropathy (HMSN) with focally folded myelin sheaths, or Charcot-Marie-Tooth type 4B (CMT4B), is a distinct clinical entity belonging to the heterogeneous group of autosomal recessive demyelinating neuropathies. We first described a large pedigree with CMT4B, which showed a high consanguinity level and an autosomal recessive pattern of inheritance. Through conventional linkage analysis, we excluded linkage of the locus segregating in this pedigree to any of the known genes responsible for other HMSNs. Using homozygosity mapping and haplotype sharing analysis, we were able to localize the disease gene in a 4 cM interval on chromosome 11q23, between the D11S1332 and D11S917 loci. On the basis of the clinical characteristics of the disease, we propose that this locus corresponds to the CMT4B gene.

Charcot-Marie-Tooth Disease↗

Cloning, genomic organization, alternative transcripts and mutational analysis of the gene responsible for autosomal recessive universal congenital alopecia.

Complete or partial congenital absence of hair (congenital alopecia) may occur isolated or with associated defects. The majority of families with isolated congenital alopecia has been reported to follow an autosomal recessive mode of inheritance (MIM 203655). We have previously mapped the gene for autosomal recessive congenital alopecia in a large inbred Pakistani family in which affected persons show complete absence of hair development (universal congenital alopecia) to a 15 cM region on chromosome 8p21-22. Here we report the cloning and characterization of the human homologue of the mouse hairless gene and show that it is located in the critical region on chromosome 8p21-22. Determining the exon-intron structure allowed detailed mutational analysis of DNA samples of patients with universal congenital alopecia. We detected a homozygous missense mutation in the Pakistani family and a homozygous splice donor mutation in a family from Oman. In addition, we show that the human hairless gene undergoes alternative splicing and that at least two isoforms generated by alternative usage of exon 17 are found in human tissues. Interestingly, the isoform containing exon 17 is the predominantly expressed isoform in all tissues but skin, where exclusive expression of the shorter isoform was observed. We speculate that this tissue-specific difference in the proportion of hairless transcripts lacking exon 17 sequences could contribute to the tissue-specific disease phenotype observed in individuals with isolated congenital alopecia.

Adult↗

An alpha-tectorin gene defect causes a newly identified autosomal recessive form of sensorineural pre-lingual non-syndromic deafness, DFNB21.

In our efforts to identify new loci responsible for non-syndromic autosomal recessive forms of deafness, DFNB loci, we have pursued the analysis of large consanguineous affected families living in geographically isolated areas. Here, we report on the study of a Lebanese family comprising nine members presenting with a pre-lingual severe to profound sensorineural isolated form of deafness. Linkage analysis led to the characterization of a new locus, DFNB21, which was assigned to chromosome 11q23-25. Already mapped to this chromosomal region was TECTA. This gene encodes alpha-tectorin, a 2155 amino acid protein which is a component of the tectorial membrane. This gene recently has been shown to be responsible for a dominant form of deafness, DFNA8/12. Sequence analysis of the TECTA gene in the DFNB21-affected family revealed a G to A transition in the donor splice site (GT) of intron 9, predicted to lead to a truncated protein of 971 amino acids. This establishes that alpha-tectorin mutations can be responsible for both dominant and recessive forms of deafness. Comparison of the phenotype of the DFNB21 heterozygous carriers with that of DFNA8/12-affected individuals supports the hypothesis that the TECTA mutations which cause the dominant form of deafness have a dominant-negative effect. The present results provide genetic evidence for alpha-tectorin forming homo- or heteromeric structures.

Base Sequence↗

A human keratin 10 knockout causes recessive epidermolytic hyperkeratosis.

Epidermolytic hyperkeratosis (EHK) is a blistering skin disease inherited as an autosomal-dominant trait. The disease is caused by genetic defects of the epidermal keratin K1 or K10, leading to an impaired tonofilament network of differentiating epidermal cells. Here, we describe for the first time a kindred with recessive inheritance of EHK. Sequence analysis revealed a homozygous nonsense mutation of the KRT10 gene in the affected family members, leading to a premature termination codon (p.Q434X), whereas the clinically unaffected consanguineous parents were both heterozygous carriers of the mutation. Semi-quantitative RT-PCR and western blot analysis demonstrated degradation of the KRT10 transcript, resulting in complete absence of keratin K10 protein in the epidermis and cultured keratinocytes of homozygous patients. This K10 null mutation leads to a severe phenotype, clinically resembling autosomal-dominant EHK, but differing in form and distribution of keratin aggregates on ultrastructural analysis. Strong induction of the wound-healing keratins K6, K16 and K17 was found in the suprabasal epidermis, which are not able to compensate for the lack of keratin 10. We demonstrate that a recessive mutation in KRT10 leading to a complete human K10 knockout can cause EHK. Identification of the heterogeneity of this disorder has a major impact for the accurate genetic counseling of patients and their families and also has implications for gene-therapy approaches.

3T3 Cells↗