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Autosomal recessive inheritance of airway hyperreactivity to 5-hydroxytryptamine.

We have previously reported that airway hyperresponsiveness to acetylcholine (ACh) is inherited as an autosomal recessive trait in A/J and C3H/HeJ mice and the progeny of crosses between them (FASEB J. 2: 2605-2608, 1988). In the present report, we have extended these studies by evaluating the biological variability in the airway response to 5-hydroxytryptamine (5-HT) and ACh among multiple genetically standardized inbred strains of mice. The pattern of airway responsiveness to ACh differed significantly from that of 5-HT in nine inbred strains of mice. A/J mice showed nonspecific airway hyperresponsiveness to both 5-HT and ACh. DBA/2J mice were hyperresponsive to 5-HT but not to ACh. An airway phenotype that resembled these inbred strains is termed HYPERREACTIVE. The C3H/HeJ and C57BL/6J inbred strains were minimally reactive to either ACh or 5-HT. Airway phenotypes that resembled these minimally reactive strains are termed HYPOREACTIVE. The frequency of HYPERRACTIVE and HYPOREACTIVE offspring from crosses between A/J and C3H/HeJ mice or DBA/2J and C57BL/6J mice is consistent with a single autosomal recessive gene, primarily determining airway hyperresponsiveness to 5-HT. We report linkage studies which suggest that these genes are not closely linked and that 5-HT and ACh airway hyperresponsiveness is inherited independently. The results of these studies suggest that murine nonspecific airway hyperresponsiveness is determined by multiple genes.

Acetylcholine↗

Localization of a recessive juvenile cataract mutation to proximal chromosome 7 in mice.

OBJECTIVE: To localize the chromosomal position of a novel cataract mutation (juvenile recessive cataract; jrc) in mice. METHODS: A mapping population was developed by crossing cataract males (albino MH) to wild-type females (black C57BL/6J). F1 females were backcrossed to albino MH males with cataracts. RESULTS: The results were consistent with a model of a single autosomal recessive gene [153 cataract, 169 wild-type; chi2 = 0.8, 1 degree of freedom (d.f.), p > 0.35]. Linkage with the albino (tyrosinase; Tyr) locus was evident (chi2 = 61.5, 1 d.f., p < 0.0001), implicating chromosome 7 as the location of jrc. Recombination percentages (+/- SE) between jrc and D7Mit340 (1.2 cM location), D7Mit227 (16.0 cM) and D7Mit270 (18.0 cM) were 17.1 +/- 2.1, 3.7 +/- 1.1 and 6.2 +/- 1.3%, respectively. Multi-point mapping determined that the most likely order of these loci is D7Mit340 - jrc - D7Mit227 - D7Mit270 - Tyr. Although animals with the mutant phenotype appeared to have little or no sense of sight, their growth was not different (p >0.20) from that of normal mice. CONCLUSION: The jrc mutation model may be useful in the study of the genetics of cataracts in other animal species, including humans.

Animals↗

Sex ratio and proportion of affected sons in sibships with X-chromosomal recessive traits: maximum likelihood estimation in truncated multinomial distributions.

If mothers are carriers of a recessive male sex-linked disorder, their children may include females, healthy males and affected males. The composition of the possible sibships follows a multinomial distribution. If the mothers are diagnosed as carriers independently of their offspring, then the distributions are not truncated, but if they are classified as carriers after the birth of at least one affected son, the distributions are truncated. In order to avoid ascertainment bias, the statistical analyses of the corresponding data must differ. We present procedures for estimation in both the untruncated and the truncated case. The formulae obtained are applied to family data for X-chromosomal recessive retinoschisis (RS) from the region of Satakunta in southwestern Finland. Earlier studies indicated that, among the offspring of RS carriers, the sex ratio was increased. In our model, therefore, we include both the proportion of males and the proportion of affected individuals among the males. The sex ratio was significantly increased (131.0), but the proportion of affected males was slightly lower than expected (42.5%). RS seems to be the only known genetic disorder in which the offspring of carriers of the mutation include a statistically significant surplus of males.

Chromosome Segregation↗

Localization of a novel autosomal recessive non-syndromic hearing impairment locus (DFNB38) to 6q26-q27 in a consanguineous kindred from Pakistan.

For autosomal recessive nonsyndromic hearing impairment over 30 loci have been mapped and 19 genes have been identified. DFNB38, a novel locus for autosomal recessive nonsyndromic hearing impairment, was localized in a consanguineous Pakistani kindred to 6q26-q27. The affected family members present with profound prelingual sensorineural hearing impairment and use sign language for communications. Linkage was established to microsatellite markers located on chromosome 6q26-q27 (Multipoint lod score 3.6). The genetic region for DFNB38 spans 10.1 cM according to the Marshfield genetic map and is bounded by markers D6S980 and D6S1719. This genetic region corresponds to 3.4 MB on the sequence-based physical map.

Chromosome Mapping↗

DFNB44, a novel autosomal recessive non-syndromic hearing impairment locus, maps to chromosome 7p14.1-q11.22.

The genetic etiology for many forms of hearing impairment (HI) is very diverse. Non-syndromic HI (NSHI) is one of the most heterogeneous traits known. Autosomal recessive forms of prelingual HI account for approximately 75% of hereditary cases. A novel autosomal recessive NSHI locus, DFNB44, was mapped to a 20.9 cM genetic interval on chromosome 7p14.1-q11.22, according to the Marshfield genetic map, in a consanguineous Pakistani family. Multipoint linkage analysis resulted in a maximum LOD score of 5.0 at marker D7S1818. The 3-unit support interval ranged from marker D7S2209 to marker D7S2435, spanning a 30.1 Mb region on the sequence-based physical map.

Chromosomes, Human, Pair 7↗

A novel autosomal recessive non-syndromic deafness locus, DFNB66, maps to chromosome 6p21.2-22.3 in a large Tunisian consanguineous family.

Hereditary non-syndromic deafness is extremely heterogeneous. Autosomal recessive forms account for approximately 80% of genetic cases. Autosomal recessive non-syndromic sensorineural deafness segregating in a large consanguineous Tunisian family was mapped to chromosome 6p21.2-22.3. A maximum lod score of 5.36 at theta=0 was obtained for the polymorphic microsatellite marker IR2/IR4. Haplotype analysis defined a 16.5-Mb critical region between microsatellite markers D6S1602 and D6S1665. The screening of 3 candidate genes, COL11A2, BAK1 and TMHS, did not reveal any disease causing mutation, suggesting that this is a novel deafness locus, which has been named DFNB66. A search in the Human Cochlear EST Library for ESTs located in this critical interval allowed us to identify several candidates. Further investigations on these candidates are needed in order to identify the deafness-causing gene in this Tunisian family.

Chromosome Mapping↗

Autosomal recessive catecholamine- or exercise-induced polymorphic ventricular tachycardia: clinical features and assignment of the disease gene to chromosome 1p13-21.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (PVT) is characterized by episodes of syncope, seizures, or sudden death in response to physiological or emotional stress. In 2 families with autosomal dominant inheritance, the disease gene was mapped to chromosome 1q42-43. The objectives of this study were to characterize the clinical features of the disease in a Bedouin tribe from Israel and to map the disease gene. METHODS AND RESULTS: In this Bedouin tribe, 9 children (age, 7+/-4 years) from 7 related families have died suddenly during the past decade, and 12 other children suffered from recurrent syncope and seizures starting at the age of 6+/-3 years. Parents of affected individuals were asymptomatic and were all related (first-, second-, or third-degree cousins). Segregation analysis suggested autosomal recessive inheritance. All 12 symptomatic patients and 1 asymptomatic sibling (mean age, 13+/-7 years) were found to have a relative resting bradycardia (64+/-13 bpm, versus 93+/-12 bpm in the unaffected siblings), as well as PVT induced by treadmill or isoproterenol infusion and appearing at a mean sinus rate of 110+/-10 bpm. Patients responded favorably to treatment with beta-blockers. A genome-wide search using polymorphic DNA markers mapped the disease locus to a 16-megabase interval on chromosome 1p13-21. A maximal lod score of 8.24 was obtained with D1S189 at theta=0.00. Sequencing of KCND3, a gene that encodes an I(tO) potassium channel transporter, did not reveal any significant sequence alterations. CONCLUSIONS: This unique form of autosomal recessive PVT affects young children and may be lethal if left untreated. Linkage analysis maps this disorder to chromosome 1p13-21.

Adolescent↗

A recessive variant of the Romano-Ward long-QT syndrome?

BACKGROUND: The congenital long-QT syndrome (LQTS) is a genetically heterogeneous disease characterized by prolonged ventricular repolarization and life-threatening arrhythmias. Mutations of the KVLQT1 gene, a cardiac potassium channel, generate two allelic diseases: the Romano-Ward syndrome, inherited as a dominant trait, and the Jervell and Lange-Nielsen syndrome, inherited as an autosomal recessive trait. METHODS AND RESULTS: A consanguineous family with the clinical phenotype of LQTS was screened for mutations in the KVLQT1 gene. Complementary RNAs for injection into Xenopus oocytes were prepared, and currents were recorded with the double microelectrode technique. A homozygous missense mutation, leading to an alanine-to-threonine substitution at the beginning of the pore domain of the KVLQT1 channel, was found in the proband, a 9-year-old boy with normal hearing, a prolonged QT interval, and syncopal episodes during physical exercise. The parents of the proband were heterozygous for the mutation and had a normal QT interval. The functional evaluation of the mutant channel activity showed reduction in total current, a hyperpolarizing shift in activation, and a faster activation rate consistent with a mild mutation likely to require homozygosity to manifest the phenotype. CONCLUSIONS: These findings provide the first evidence for a recessive form of the Romano-Ward long-QT syndrome and indicate that homozygous mutations on KVLQT1 do not invariably produce the Jervell and Lange-Nielsen syndrome. The implications of this observation prompt a reconsideration of the penetrance of different mutations responsible for LQTS and suggest that mild mutations in LQTS genes may be present among the general population and may predispose to drug-induced ventricular arrhythmias.

Child↗

A nonsense mutation in the glucosaminyl (N-acetyl) transferase 2 gene (GCNT2): association with autosomal recessive congenital cataracts.

PURPOSE: To identify the genetic defect associated with autosomal recessive congenital cataract in four Arab families from Israel. METHODS: Genotyping was performed using microsatellite markers spaced at approximately 10 cM intervals. Two-point lod scores were calculated using MLINK of the LINKAGE program package. Mutation analysis of the glucosaminyl (N-acetyl) transferase 2 gene (GCNT2) gene was performed by direct sequencing of PCR-amplified exons. RESULTS: The cataract locus was mapped to a 13.0-cM interval between D6S470 and D6S289 on Chr. 6p24. A maximum two-point lod score of 8.75 at theta = 0.019 was obtained with marker D6S470. Sequencing exons of the GCNT2 gene, mutations of which have been associated with cataracts and the i blood group phenotype, revealed in these families a homozygous G-->A substitution in base 58 of exon-2, resulting in the formation of premature stop codons W328X, W326X, and W328X, of the GCNT2A, -B, and -C isoforms, respectively. Subsequent blood typing of affected family members confirmed the possession of the rare adult i blood group phenotype. CONCLUSIONS: A nonsense mutation in the GCNT2 gene isoforms is associated with autosomal recessive congenital cataract in four distantly related Arab families from Israel. These findings provide further insight into the dual role of the I-branching GCNT2 gene in the lens and in reticulocytes.

Arabs↗

Early-onset, autosomal recessive, progressive retinal atrophy in Persian cats.

PURPOSE: An early-onset retinal degenerative disease has been identified in Persian cats. This study genetically, clinically, and histologically characterized the disease. A breeding colony was established to assist with identification of the causative gene and to provide a resource for vision research. METHODS: Cats were produced from testcross breedings. Kittens underwent serial ophthalmic and neuro-ophthalmic examinations. Globes were harvested from age-matched affected, obligate carrier, and control cats and were evaluated by light microscopy. Fluorescein angiography assessed retinal and choroidal vasculature. RESULTS: Test breedings confirmed an autosomal recessive mode of inheritance. Rate and extent of disease progression were similar among individual affected cats. The earliest clinical signs (reduced pupillary light reflexes) were seen at 2 to 3 weeks of age. Retinal degeneration was virtually complete by 16 weeks of age. Histologic changes progressed rapidly and paralleled clinical findings. Histologic lesions were limited to the photoreceptors, outer plexiform layer, and retinal pigment epithelium in all but the terminal stages, when subtle changes were noted within the inner nuclear layer. CONCLUSIONS: Characterized in this study was an autosomal recessive, early-onset, retinal degenerative disease in Persian cats that is likely to be more prevalent in this breed than previously suspected. This feline disease model may identify a new gene or provide biological insight into some forms of early-onset retinitis pigmentosa (RP) in humans and genetic retinal degenerations in other species. A breeding colony that will assist in the identification of the causative gene has been established and is available for studies in vision research.

Animals↗

Mutations in betaB3-crystallin associated with autosomal recessive cataract in two Pakistani families.

PURPOSE: To identify the disease locus for autosomal recessive congenital cataracts in consanguineous Pakistani families. METHODS: Two Pakistani families were ascertained, patients were examined, blood samples were collected, and DNA was isolated. A genome-wide scan was performed using >382 polymorphic microsatellite markers on genomic DNA from affected and unaffected family members. Two-point lod scores were calculated, haplotypes were formed by inspection, and candidate genes were sequenced. Real-time quantitative PCR techniques were used to determine the mRNA levels, and molecular modeling was performed to gain a better understanding of the significance of the disease-causing mutation. RESULTS: In the genome-wide scan, maximum lod scores of 2.67 and 2.77 for family 60004 and 2.02 and 2.04 for family 60006 were obtained for markers D22S539 and D22S315, respectively. The linked region, 22.7 cM (10 Mb) flanked by markers D22S420 and D22S1163, contains the beta-crystallin gene cluster including the genes CRYBA4, CRYBB1, CRYBB2, and CRYBB3. Sequencing of these genes showed a G-->C transition in exon 6 of CRYBB3 resulting in a p.G165R change in the betaB3-crystallin protein that cosegregates with the disease in both families. Real-time PCR analysis suggested that betaB3-crystallin mRNA levels approximate those of other betagamma-crystallins. Molecular modeling predicted changes in electrostatic potential that would be expected to reduce the stability of the fourth Greek-key motif, and hence the entire protein, dramatically. CONCLUSIONS: For the first time, a mutation in CRYBB3 is reported in two consanguineous Pakistani families with autosomal recessive congenital cataracts.

Amino Acid Sequence↗

Elevated n-alkanes in congenital ichthyosiform erythroderma. Phenotypic differentiation of two types of autosomal recessive ichthyosis.

Previously considered to represent a single genetic disorder, autosomal recessive ichthyosis was examined in clinical and lipid biochemical studies of 18 patients with this condition and instead disclosed to be two distinct diseases. Six patients displayed clinical features of classical lamellar ichthyosis (LI), which is characterized by monomorphous features, including large, dark, platelike scales, severe ectropion, and a uniformly severe, unremitting course. 11 patients displayed clinical features of nonbullous congenital ichthyosiform erythroderma (CIE) characterized by fine white scales, prominent erythroderma, a milder course, and a variable prognosis. CIE could be separated biochemically from LI by the invariable presence of elevated quantities of n-alkanes in scale (CIE, 24.8 +/- 1.9% vs. LI, 7.2 +/- 1.6%, and normal, 6.5 +/- 0.9%), which suggested a primary disorder in neutral lipid metabolism. In light of the distinctive clinical features of each, these biochemical studies indicate that autosomal recessive ichthyosis comprises two distinct disorders.

Alkanes↗

Mapping the gene causing X-linked recessive idiopathic hypoparathyroidism to Xq26-Xq27 by linkage studies.

Idiopathic hypoparathyroidism has been reported to occur as an X-linked recessive disorder in two multigeneration kindreds. Affected individuals, who are males, suffer from infantile onset of epilepsy and hypocalcemia, which appears to be due to an isolated congenital defect of parathyroid gland development; females are not affected and are normocalcemic. We have performed linkage studies in these two kindreds (5 affected males, 11 obligate carrier females, and 44 unaffected members) and have used cloned human X chromosome sequences identifying restriction fragment length polymorphisms to localize the mutant gene causing this disorder. Our studies established linkage between the X-linked recessive idiopathic hypoparathyroid gene (HPT) and the DXS98 (4D.8) locus, peak LOD score = 3.82 (theta = 0.05), thereby mapping HPT to the distal long arm of the X chromosome (Xq26-Xq27). Multilocus analysis indicated that HPT is proximal to the DXS98 (4D.8) locus but distal to the F9 (Factor IX) locus, thereby revealing bridging markers for the disease. The results of this study will improve genetic counseling of affected families, and further characterization of this gene locus will open the way for elucidating the factors controlling the development and activity of the parathyroid glands.

Chromosome Mapping↗

Premature termination codons on both alleles of the type VII collagen gene (COL7A1) in three brothers with recessive dystrophic epidermolysis bullosa.

Epidermolysis bullosa (EB) is a group of heritable mechano-bullous skin diseases classified into three major categories on the basis of the level of tissue separation within the dermal-epidermal basement membrane zone. In the most severe, dystrophic (scarring) forms of EB, blisters form below the cutaneous basement membrane at the level of the anchoring fibrils, which are composed of type VII collagen. Ultrastructural observations of altered anchoring fibrils and genetic linkage to the type VII collagen locus (COL7A1) have implicated COL7A1 as the candidate gene in the dystrophic forms of EB. We have recently cloned the entire cDNA and the gene for human COL7A1. In this study, we describe distinct mutations in both COL7A1 alleles in three brothers with severe, mutilating recessive dystrophic EB (the Hallopeau-Siemens type, HS-RDEB). The patients are compound heterozygotes for two different mutations, both of which result in a premature termination codon in COL7A1, and the parents were shown to be clinically heterozygous carries of the respective mutations. Premature termination codons in both alleles of COL7A1 appear to be the underlying cause of severe, recessive dystrophic EB in this family.

Adolescent↗

Novel AE1 mutations in recessive distal renal tubular acidosis. Loss-of-function is rescued by glycophorin A.

The AE1 gene encodes band 3 Cl-/HCO3- exchangers that are expressed both in the erythrocyte and in the acid-secreting, type A intercalated cells of the kidney. Kidney AE1 contributes to urinary acidification by providing the major exit route for HCO3- across the basolateral membrane. Several AE1 mutations cosegregate with dominantly transmitted nonsyndromic renal tubular acidosis (dRTA). However, the modest degree of in vitro hypofunction exhibited by these dRTA-associated mutations fails to explain the disease phenotype in light of the normal urinary acidification associated with the complete loss-of-function exhibited by AE1 mutations linked to dominant spherocytosis. We report here novel AE1 mutations linked to a recessive syndrome of dRTA and hemolytic anemia in which red cell anion transport is normal. Both affected individuals were triply homozygous for two benign mutations M31T and K56E and for the loss-of-function mutation, G701D. AE1 G701D loss-of-function was accompanied by impaired trafficking to the Xenopus oocyte surface. Coexpression with AE1 G701D of the erythroid AE1 chaperonin, glycophorin A, rescued both AE1-mediated Cl- transport and AE1 surface expression in oocytes. The genetic and functional data both suggest that the homozygous AE1 G701D mutation causes recessively transmitted dRTA in this kindred with apparently normal erythroid anion transport.

Acidosis, Renal Tubular↗

Evidence for autosomal recessive inheritance in 46 families with multiple incidences of autism.

The authors ascertained 46 families with multiple incidences of autism (41 with two and five with three autistic probands). Classical segregation analyses revealed a maximum likelihood estimate of the segregation ratio of p = 0.19 +/- 0.07. This is not significantly less than 0.25, the expected value for autosomal recessive inheritance. However, it is significantly less than 0.50, the expected value for autosomal dominant inheritance. The polygenic threshold model was tested and rejected over a full range of values of heritability and ascertainment probability for these families. These results are most consistent with the hypothesis of autosomal recessive inheritance in this subset of 46 families with multiple incidences of autism.

Adolescent↗

Orthodontic treatment and isolated gingival recession: a review.

Isolated gingival recession may occur in as many as 30 per cent of adolescents, and lead to problems of dentine hypersensitivity, root caries, and gingival inflammation in adult life. This review discusses the prevalence and aetiology of isolated recession, with particular reference to the implications for orthodontic treatment. Consideration is also given to the differing philosophies for management.

Adolescent↗

A novel variant of biallelic MME gene associated with autosomal recessive late-onset distal hereditary motor neuropathy in Chinese families.

Distal hereditary motor neuropathies (dHMN) are a group of heterogeneous diseases and previous studies have reported that the compound heterozygous recessive MME variants cause dHMN. Our study found a novel homozygous MME variant and a reported compound heterozygous MME variant in two Chinese families, respectively. Next-generation sequencing and nerve conduction studies were performed for two probands. The probands in two families presented with the muscle weakness and wasting of both lower limbs and carried a c.2122&#xa0;A&#x2009;>&#x2009;T (p.K708*) and c.1342&#xa0;C&#x2009;>&#x2009;T&c.2071_2072delinsTT (p.R448*&p.A691L) variant, respectively. Prominently axonal impairment of motor nerves and slight involvement of sensory nerves were observed in nerve conduction study. Our study reported a "novel" nonsense mutation and a missense variant of autosomal recessive late-onset dHMN and reviewed reported MME variants associated with dHMN phenotype.

Adult↗