Genetics and early disturbances of breathing control

Early disturbances in breathing control, including apneas of prematurity and apparently life-threatening events, account for some cases of sudden infant death syndrome and for a rare disorder called congenital central hypoventilation syndrome (CCHS). Data suggesting a genetic basis for CCHS have been obtained. Recently, we found heterozygous de novo mutations of the PHOX2B gene in 18 of 29 individuals with CCHS. Most mutations consisted of five to nine alanine expansions within a 20-residue polyalanine tract, probably resulting from nonhomologous recombination. Other mutations, generally inherited from one of the parents, in the coding regions of genes involved in the endothelin and RET signaling pathways and in the brain-derived-neurotrophic factor (BDNF) gene have been found in a few CCHS patients. Interestingly, all these genes are involved in the development of neural crest cells. Targeted disruption of these genes in mice has provided information on the pathophysiological mechanisms underlying CCHS. Despite the identification of these genes involved in breathing control, none of the genetically engineered mice developed to date replicate the full human CCHS respiratory phenotype. Recent insights into the genetic basis for CCHS may shed light on the genetics of other early disturbances in breathing control, such as apnea of prematurity and sudden infant death syndrome.     

A cognitive characterization of dyscalculia in Turner syndrome

Current theories of number processing postulate that the human abilities for arithmetic are based on cerebral circuits that are partially laid down under genetic control and later modified by schooling and education. This view predicts the existence of genetic diseases that interfere specifically with components of the number system. Here, we investigate whether Turner syndrome (TS) corresponds to this definition. TS is a genetic disorder which affects one woman in 2500 and is characterized by partial or complete absence of one X chromosome. In addition to well-characterized physical and hormonal dysfunction, TS patients exhibit cognitive deficits including dyscalculia. We tested 12 women with Turner syndrome and 13 control subjects on a cognitive battery including arithmetical tests (addition, subtraction, multiplication, division) as well as tests of the understanding of numerosity and quantity (cognitive estimation, estimation, comparison, bisection, subitizing/counting). Impairments were observed in cognitive estimation, subitizing, and calculation. We examine whether these deficits can be attributed to a single source, and discuss the possible implications of hormonal and genetic factors in the neuropsychological profile of TS patients.     

Impaired autonomic control of the heart by SOX10 mutation

The autonomic nervous system plays an important role in the generation of complex heart rate dynamics that enable an organism to adapt to stress. Little is known about genes influencing the development of this autonomic control of the heart. We suggest the SOX10 gene to be a candidate for this process.     

Colonic fermentation influences lower esophageal sphincter function in gastroesophageal reflux disease

BACKGROUND & AIMS: Colonic fermentation of carbohydrates is known to influence gastric and esophageal motility in healthy subjects. This study investigated the effects of colonic fermentation induced by oral administration of fructooligosaccharides (FOS) in patients with gastroesophageal reflux disease (GERD). METHODS: In the cross-over design used in the study, 9 patients with symptomatic GERD were administered a low-residue diet (i.e., 10 g fiber/day) during 2, 7-day periods, receiving either 6.6 g of FOS or placebo 3 times daily after meals. Each period was separated by a wash out of at least 3 weeks. On day 7, esophageal motility and pH were recorded in fasting conditions and after a test meal containing 6.6 g of FOS or placebo. Breath hydrogen concentrations (reflecting colonic fermentation) and plasma concentrations of glucagon-like peptide 1 (GLP-1), peptide YY, and cholecystokinin were monitored. RESULTS: Compared with placebo, FOS led to a significant increase in the number of transient lower esophageal sphincter relaxations (TLESRs) and reflux episodes, esophageal acid exposure, and the symptom score for GERD. The integrated plasma response of GLP-1 was significantly higher after FOS than placebo. CONCLUSIONS: Colonic fermentation of indigestible carbohydrates increases the rate of TLESRs, the number of acid reflux episodes, and the symptoms of GERD. Although different mechanisms are likely to be involved, excess release of GLP-1 may account, at least in part, for these effects.