The cohesin complex is a major constituent of interphase and mitotic chromosomes. Apart from its role in mediating sister chromatid cohesion, it is also important for DNA double-strand-break repair and transcriptional control. The functions of cohesin are regulated by phosphorylation, acetylation, ATP hydrolysis, and site-specific proteolysis. Recent evidence suggests that cohesin acts as a novel topological device that traps chromosomal DNA within a large tripartite ring formed by its core subunits.

Cohesin: Its Roles and Mechanisms

The decline in the high incidence of amyotrophic lateral sclerosis, parkinsonism, and Alzheimer-type dementia among the Chamorro population of the western Pacific islands of Guam and Rota, coupled with the absence of demonstrable viral and hereditable factors in this disease, suggests the gradual disappearance of an environmental factor selectively associated with this culture. One candidate is seed of the neurotoxic plant Cycas circinalis L., a traditional source of food and medicine which has been used less with the Americanization of the Chamorro people after World War II. Macaques were fed the Cycas amino acid beta-N-methylamino-L-alanine, a low-potency convulsant that has excitotoxic activity in mouse brain, which is attenuated by N-methyl-D-aspartate receptor antagonists. These animals developed corticomoto-neuronal dysfunction, parkinsonian features, and behavioral anomalies, with chromatolytic and degenerative changes of motor neurons in cerebral cortex and spinal cord. In concert with existing epidemiological and animal data, these findings support the hypothesis that cycad exposure plays an important role in the etiology of the Guam disease.

https://science.sciencemag.org/content/sci/237/4814/517.full.pdf

Guam amyotrophic lateral sclerosis-parkinsonism-dementia linked to a plant excitant neurotoxin

Kallmann's syndrome (clinically characterized by hypogonadotropic hypogonadism and inability to smell) is caused by a defect in the migration of olfactory neurons, and neurons producing hypothalamic gonadotropin-releasing hormone. A gene has now been isolated from the critical region on Xp22.3 to which the syndrome locus has been assigned: this gene escapes X inactivation, has a homologue on the Y chromosome, and shows an unusual pattern of conservation across species. The predicted protein has significant similarities with proteins involved in neural cell adhesion and axonal pathfinding, as well as with protein kinases and phosphatases, which suggests that this gene could have a specific role in neuronal migration.

A gene deleted in Kallmann's syndrome shares homology with neural cell adhesion and axonal path-finding molecules.

The emerging awareness of the contribution of epigenetic processes to genome function in health and disease is underpinned by decades of research in model systems. In particular, many principles of the epigenetic control of genome function have been uncovered by studies of genomic imprinting. The phenomenon of genomic imprinting, which results in some genes being expressed in a parental--origin-specific manner, is essential for normal mammalian growth and development and exemplifies the regulatory influences of DNA methylation, chromatin structure and non-coding RNA. Setting seminal discoveries in this field alongside recent progress and remaining questions shows how the study of imprinting continues to enhance our understanding of the epigenetic control of genome function in other contexts.

Genomic imprinting: The emergence of an epigenetic paradigm

The heritable disorders of connective tissue have proven to be very heterogeneous and problems have arisen concerning syndromic boundaries, nomenclature, and classification. In an attempt to resolve these dilemmas, a group of experts participated in a Workshop held during the 7th International Congress of Human Genetics, Berlin, in September, 1986. At the Workshop, overviews were given of the uses and limitations of nosology (McKusick), diagnostic criteria (Pyeritz), and practical issues in biochemical and molecular diagnosis (Hollister). Invited speakers then gave brief comments on the current status of the nosology of specific categories of inherited connective tissue disorders and made recommendations for possible modification. The Workshop was followed by two closed committee meetings at which the participants attempted to reach agreement on syndromic definition and a standardized nomenclature. The final proposals, with brief comment where relevant, form the subject of this communication.

International Nosology of Heritable Disorders of Connective Tissue, Berlin, 1986.

Eight patients (4 males, 4 females) were affected with a previously undefined multiple congenital anomalies/mental retardation syndrome which was designated the Cardio-Facio-Cutaneous (CFC) syndrome and which includes congenital heart defects, characteristic facial appearance, ectodermal abnormalities, and growth failure. Cardiac defects were variable, the most common being pulmonic stenosis and atrial septal defect. Typical facial characteristics were high forehead with bitemporal constriction, hypoplasia of supraorbital ridges, antimongoloid slant of palpebral fissures, depressed bridge of nose, and posteriorly angulated ears with prominent helices. The hair was usually sparse and friable. Skin changes varied from patchy hyperkeratosis to a severe generalized ichthyosis-like condition. All cases were sporadic in occurrence, there was no family history of consanguinity, and chromosomes were normal. Although presumed to be genetic, the cause of the CFC syndrome remains unknown.

New multiple congenital anomalies/mental retardation syndrome with cardio-facio-cutaneous involvement―The CFC syndrome

On the basis of studies in two brothers and their double first cousin, the Kallmann syndrome (KS) is discussed as an X-linked syndrome of anosmic hypogonadotropic hypogonadism. The anosmia is thought to represent agenesis or hypoplasia of the olfactory lobes, the mildest form of the alobar holoprosencephaly developmental field defect; this is supported by the finding of hypotelorism in two of the patients and their mother. The endocrine defect is thought to represent a hypothalamic abnormality of the luteinizing hormone releasing hormone; borderline normal intelligence may represent another pleio-tropic CNS manifestation of the KS gene. All three affected males had unilateral renal aplasia, associated in one with ipsilateral absence of the testis. The presence of at least two developmental field defects (involving the CNS and urogenital system) makes it likely that the KS is a true multiple congenital anomaly syndrome; this is supported by the finding of additional, mostly minor, anomalies reported by other investigators. Heterozygous females may also show manifestations of anosmia, hypogonadism, possibly even internal genital malformation; however, genetic heterogeneity of anosmic hypogonadism is possible, and for the time being it is probably better to designate sporadic female cases of anosmic hypogonadism as examples of the olfacto-genital syndrome of DeMorsier. Linkage studies are urgently needed to clear up the question of genetic heterogeneity and to help develop empiric recurrence risk figures in anosmic hypogonadism.

Familial Kallmann syndrome with unilateral renal aplasia.

Patients with Poland syndrome were ascertained through the British Columbia Health Surveillance Registry, through hospital records, and through practicing plastic and orthopedic surgeons. Of 44 patients who were ascertained, 28 had family histories taken and were examined. Physical findings were: absence of the sternal head of the pectoralis major in all patients, symbrachydactyly in most patients, and infrequent other associations such as imsilateral undescended testis, Mobius syndrome, clubfoot and submucous cleft palate. Family histories were “negative” in all cases. The 8 affected adults had 24 reportedly normal children. Mean paternal age was significantly higher than the paternal age in the population. The incidence was 1 /32,000 livebirths in British Columbia. It was concluded that in the British Columbia population the syndrome is usually a sporadic event.

Poland syndrome in British Columbia: incidence and reproductive experience of affected persons.

Three of our own and 38 previously reported cases of cutis marmorata telangiectatica congenita (CMTC) are reviewed. Light and electronmicroscopic studies revealed atypical capillaries, venules, and veins in different cutaneous layers. Clinically, the lesions are manifested as telangiectasis, capillary hemangioma, cutis marmorata, venous hemangioma and varicose veins, depending on the type of vessels involved and the layer of skin affected. Secondary thrombosis with subsequent localized atrophy and ulceration occurs in a substantial number of cases. In at least 50% of cases there are associated findings. Hypoplasia or hyperplasia of „affected” or of „unaffected” organs is the most common association. Overwhelming sporadic occurrence, female reponderance, occasional minor manifestations in close relatives and considerable clinical variability suggest a multi-factorial etiology of CMTC.

Jürgen Herrmann

Papers

New multiple congenital anomalies/mental retardation syndrome with cardio-facio-cutaneous involvement―The CFC syndrome

Familial Kallmann syndrome with unilateral renal aplasia.

Poland syndrome in British Columbia: incidence and reproductive experience of affected persons.

Cutis marmorata telangiectatica congenita.

The Stickler syndrome (hereditary arthroophthalmopathy).