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Genetics of juvenile diabetes mellitus. A recessive gene closely linked to HLA D and with 50 per cent penetrance.

We investigated the genetic predisposition to juvenile diabetes in the families of 31 index cases in relation to the inheritance of the HLA system. The diabetes-predisposing gene was found to be recessive because the diabetic sibs in index cases shared both their HLA genes with a significantly increased frequency. Penetrance was estimated at 50 per cent because half the HLA-identical sibs in index cases were diabetic. These conclusions fit with published observations that the risk to sibs of patients is about 100 per cent, when both parents are normal. In three informative cases of recombination within HLA the predisposing gene traveled with the HLA D segment of the recombinant haplotype. We prepared tables for the computation of risks to relatives, based on the hypothesis of recessivity, HLA linkage and 50 per cent penetrance.

Adolescent

Three recessive genes for congenital osteopetrosis in Norway rat.

In the rat, the autosomal recessive toothless (t1) mutation exhibits an acute form of osteopetrosis. This gene is not an allele of either ia or op that causes respectively, a transitory and acute form of the disease. Comparative radiographic study of t1/t1 and op/op mutants reveals some differences in respect to the size and shape of long bones. In contrast to op/op mutants, homozygous t1/t1 animals failed to respond to either parabiosis or bone marrow transplants.

Alleles

Further study of the X-linked recessive gene hypothesis for inheritance of spatial abilities.

Two measures of spatial ability were administered to 319 undergraduates, 93 parents, and 62 siblings. Although males outperformed females on both tests, the resulting correlational pattern did not conform to the trait pattern hypothesized on the basis of an X-linked recessive trait. Results from a pedigree analysis, however, were in the expected direction. The inclusion of pedigree analyses is urged in future research.

Female

Genetic Ancestry and Carrier Variant Frequency Enrichment in a Colombian Andean Population: Insights From the Eje Cafetero.

Colombia is one of the most genetically diverse populations in Latin America, and its demographic process has promoted the persistence and local enrichment of deleterious alleles, increasing the frequency of autosomal recessive disorders, particularly in semi-isolated Andean populations such as the Eje Cafetero. However, exome-based reference data from this region remain scarce, limiting ancestry-aware variant interpretation and carrier screening strategies. We aimed to characterize the ancestry proportions of this population using exome data, and to estimate the carrier frequency and distribution of pathogenic and likely pathogenic (P/LP) variants in clinically relevant recessive genes. We conducted a cross-sectional study with whole-exome sequencing (WES) in 316 unrelated individuals from the Colombian Eje Cafetero. P/LP variants were evaluated in 454 genes associated with autosomal recessive disorders. The global ancestry proportions were estimated using a validated panel of 250 exome-compatible ancestry-informative markers. Carrier frequencies were compared against Non-Finnish Europeans (NFE) and Admixed Americans (AMX) from gnomAD v4. The cohort showed predominant European ancestry (mean 51%), followed by Native American (36%) and African (13%) components. We identified 151 carriers of 89 distinct pathogenic variants across autosomal recessive genes. The most frequent variants were SERPINA1 c.863A>T (5.5%), CFTR c.1210-11T>G (3.5%), and PYGM c.1094C>T (1.5%). Also, recurrent variants were significantly enriched compared with both NFE and AMX populations, supporting regional founder effects. This study represents one of the most comprehensive exome-based genetic characterizations of the Colombian Eje Cafetero, revealing ancestry-specific enrichment of clinically relevant autosomal recessive variants driven by founder effects.

Female

Congenital hereditary bilateral nonattachment of retina: a sibship of two males.

Two brothers, the only two children of nonconsanguineous parents, have no perception of light, bilateral microphthalmos, and degenerative corneal opacities that just allow observation of shallow anterior chambers and cataracts. The right eye of the older was removed at the age of 6 weeks: "congenital retinal detachment" was found. The birth of a subsequent affected son suggests that recessive genes are responsible. An X-linked gene is calculated to be more likely than autosomal recessive genes. These two males may suffer from a form of Norrie's disease without mental deficiency, however, they may be examples of the severest form of "falciform retinal folds" (autosomal recessive) or they may represent the same end-result from a different inherited pathological process. After the birth of the first affected child, the parents had been reassured that this undiagnosed, and at that time unknown condition, would not affect future children. The tragedy of a second affected child followed. We suggest that recessive genes (autosomal or X-linked) be specifically considered--with literature search--in any sporadic case of a bilateral symmetrical condition of the eyes not hitherto well known, especially if congenital, and in the absence of consanguinity of parents affected males in previous maternal generations. The possibility of a dominant mutation when a single case occurs in a sibship should also be considered.

Genes, Recessive

Mutagenicity studies with 5-thio-D-glucose. Cytogenetic investigation in mice, and the sex-linked recessive lethal gene test in Drosophila.

Cytogenetic studies in bone marrow cells and dividing spermatocytes I in male mice and the sex-linked recessive lethal gene test in Drosophila melanogaster were initiated to evaluate the mutagenic potential of 5-thio-D-glucose, a reversible male contraceptive in some mammals. The compound was administered by oral intubation to mice at 40 or 60 mg/kg for various time periods. Oregon-R D. melanogaster males were fed medium containing 600 or 1200 ppm of the substance for 72 hours and mated with virgin Muller-5 females to test for gene mutation. The compound did not enhance structural and numerical chromosomal aberrations or elevate sex-linked recessive lethals in D. melanogaster. It is concluded that under the conditions of the present study 5-thio is a nonmutagenic male antifertility agent.

Animals

Form and pattern in ciliated protozoa: analysis of a genic mutant with altered cell shape in Tetrahymena pyriformis, Syngen 1.

A single cell isolated from the sexual progeny of mutagenized parents gave rise to a clone of cells with an abnormal, conical shape. Breeding analysis revealed that this shape results from the action of a single recessive gene, co (conical). Homozygous mutant cells are shorter and wider than wild type cells, and have their widest point at a more posterior position. Nonetheless, cortical parameters such as number of ciliary rows, number of ciliary units within these rows, and positions of contractile vacuole pores remain essentially unchanged in conical cells, suggesting a considerable degree of mutual independence of pattern and form. Shape changes prior to cell division bring about some convergence in form of dividing conical and wild type cells. However, in conical cells the new oral apparatus and fission line form well posterior to the cell equator, so the opisthes are invariably smaller than proters. Macronuclei nonetheless undergo constriction at the normal central location, and the characteristic inequality in the DNA content of the two macronuclear division products is not increased by the conical condition. Generation times are, on the average, nearly the same in the two wild type daughter cells and in conical proters, while the small conical opisthes have generation times averaging one-third longer. This prolongation explains why population doubling times are always somewhat longer in cultures of conical cells than in parallel cultures of wild type cells. The unusually long generation times of conical opisthes allows for the compensation of initial size differences. Observations on shape changes in conjugating cells of various genotypic combinations suggest that the wild type gene product is not freely exchangeable across the conjugation bridge. The implications of the conical phenotype for problems of cellular patterning and positioning of organelle systems are considered in the discussion.

Alleles

Nuclear transplantation in Bombina orientalis and utilization of the Pale mutation as a nuclear marker.

The discoglossid frog, Bombina orientalis, displays many characteristics that make it desirable as a laboratory animal. We report here the first successful transplantation of embryonic nuclei into enucleated eggs of this organism. The participation of the grafted nucleus in the development of the transplant embryos was confirmed with the use of a genetic marker, the Pale mutation. Frogs homozygous for this recessive gene are much lighter in appearance than the wild-type animals. The use of this trait in appropriate experiments demonstrated that nuclear transplantation in B. orientalis provides embryos whose nuclei may be reliably interpreted as being derived from the injected nucleus.

Animals

Limbless: a new genetic mutant in the chick.

A mutation in the chicken resulting in total amelia is described. Genetic analysis indicates that the limbless condition is due to an autosomal recessive gene. In the limbless embryos the apical ectodermal ridge is lacking. However both the pectoral and pelvic girdles as well as the respiratory and excretory systems are normal. In the affected embryos usually the upper beak is shorter than the lower beak.

Animals

Salivary peroxidase (SAPX): genetic modification and relationship to the proline-rich (Pr) and acidic (Pa) proteins.

There is genetic polymorphism of the peroxidase of human saliva, but not of leukocytes. The phenotypes are determined by autosomal inheritance, the phenotype of fast mobility (SAPX 1) being determined by homozygosity for a recessive gene (SAPX1) and the phenotypes of slow mobility (SAPX 2 and SAPX 3) being determined by two different genes, SAPX2 and SAPX3, with completely dominant expression at the same locus. The phenotypes are modified by varying degrees of endogenous proteolysis. The SAPX 2 and SAPX 3 types appear to be genetically controlled modifications of SAPX 1 rather than different primary gene products, because of their completely dominant inheritance, their larger molecular size compared to SAPX 1, and their dissociation with 2-mercaptoethanol to give SAPX 1. The acidic protein type Pa 1 is always found in association with SAPX 2, and an uncommon variant type Pa 2 is associated with SAPX 3. The most likely hypothesis is that the genes Pa1 and Pa2 produce products which modify the SAPX 1 type. When the Pa type is Pa 0, the SAPX phenotype is SAPX 1. Since 2-mercaptoethanol can dissociate the Pa 1 protein into a probable monomeric form, and can dissociate SAPX 2 and SAPX 3 to give SAPX 1, it is probable that Pa 1 and Pa 2 monomers complex with SAPX 1 through disulfide bonds to give SAPX 2 or SAPX 3 types. The frequencies of the genes determining the SAPX types are the same as those for Pa: SAPX1 and Pa0 = 0.787, SAPX2 and Pa1 = 0.208, SAPX3 and Pa2 = 0.005.

Electrophoresis, Polyacrylamide Gel

International collaborative study of the spinal muscular atrophies. Part 2. Analysis of genetic data.

Most of the cases in the present study are of the juvenile onset, proximal form of spinal muscular atrophy. The results of the study indicate that the majority of these cases are due to one or more autosomal recessive genes, with very few being inherited as a dominant trait. Affected individuals very widely in the severity of the disease. When 2 or more sibs are affected, they tend to be similar as regards severity, but there are a substantial number of sibships in which this is not so. The data are consistent with either a single gene, with a wide range of expressivity due to the effects of other genes and/or environmental influences, or 2 or more genes, but with considerable overlap in their expression.

Adolescent

Distal spinal muscular atrophy. A clinical and genetic study of 8 kindreds.

Twelve patients (8 kindreds) with distal SMA are described, and an analysis presented of their clinical and genetic features. Distal SMA accounted for 10% of all patients with SMA in a total population survey of this disease in North-East England. The parental consanguinity rate is high, occurring in 3 of the 8 kindreds reported; the sex ratio was 1.0; the segregation ratio of sibs did not differ from 0.25. Intrafamilial concordance for clinical features of the disease is high. This current data is consistent with a suggested aetiology of two separate autosomal recessive genes. Clinical features are discussed and a review of the literature presented. The disease is only slowly progressive, but one of the genetic types may present with infantile or early juvenile onset; there is no evidence that it shortens life. 50% of cases did not have a normal gait after 4 years of age; 50% could not run after 17 years of age; and 50% could not walk unaided after 28 years of age. Details of prognosis, and principles of genetic counselling in this disease are discussed.

Adolescent

Three siblings with premature gonadal failure.

Of a brother and two sisters with infertility, one female sibling was found to be mosaic for Turner's syndrome. The brother and the other sister, of average intelligence, were phenotypically normal, with no dysmorphic features or ambiguous genitalia, but both showed hypergonadotropic hypogonadism. It is suggested that the basic defect in these two siblings is the same and is of genetic origin. As the parents were consanguineous, the defect is most likely due to an autosomal recessive gene.

Female