Biomedical subjects
Satu Kivitie-Kallio
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Delineation of Cohen syndrome following a large-scale genotype-phenotype screen.
Cohen syndrome is an autosomal recessive condition associated with developmental delay, facial dysmorphism, pigmentary retinopathy, and neutropenia. The pleiotropic phenotype, combined with insufficient clinical data, often leads to an erroneous diagnosis and has led to confusion in the literature. Here, we report the results of a comprehensive genotype-phenotype study on the largest cohort of patients with Cohen syndrome assembled to date. We found 22 different COH1 mutations, of which 19 are novel, in probands identified by our diagnostic criteria. In addition, we identified another three novel mutations in patients with incomplete clinical data. By contrast, no COH1 mutations were found in patients with a provisional diagnosis of Cohen syndrome who did not fulfill the diagnostic criteria ("Cohen-like" syndrome). This study provides a molecular confirmation of the clinical phenotype associated with Cohen syndrome and provides a basis for laboratory screening that will be valuable in its diagnosis.
Somatosensory evoked potentials and magnetic fields elicited by tactile stimulation of the hand during active and quiet sleep in newborns.
OBJECTIVE: Our objective was to characterize the effects of sleep stages on tactile somatosensory evoked responses in full-term newborns. METHODS: Somatosensory evoked potentials (SEPs) and magnetic fields (SEFs) to tactile stimulation of the tip of the index finger and/or thenar eminence were measured from 14 healthy newborns. The stimulus was a gentle tap produced by a moving membrane driven by an air-pressure pulse. RESULTS: SEPs and SEFs to tactile stimulation of the skin were similar in waveform and latency to SEPs known to be produced by electrical stimulation of the fingertip of neonates. The two most distinguishable positive deflections of SEPs, P1 and P2, within 300 ms of the stimulation, and their magnetic counterparts were clearly smaller in active compared to quiet sleep. CONCLUSIONS: Our study demonstrates for the first time that it is possible to record SEFs in neonates, and that clear late cortical somatosensory responses are produced by tactile stimulation. In addition, the effect of sleep stage on these responses indicates differences in the processing of the incoming information, at least in the somatosensory modality, in active and quiet sleep. SIGNIFICANCE: Tactile stimulation may be useful as a completely non-invasive technique for studying the physiology of the somatosensory system in neonates. Methodologically, since the effect of sleep stage is profound, one must carefully monitor the sleep stages in studies of event-related responses in newborns, or else this effect may confound the phenomena being studied.
Cohen syndrome is caused by mutations in a novel gene, COH1, encoding a transmembrane protein with a presumed role in vesicle-mediated sorting and intracellular protein transport.
Cohen syndrome is an uncommon autosomal recessive disorder whose diagnosis is based on the clinical picture of nonprogressive psychomotor retardation and microcephaly, characteristic facial features, retinal dystrophy, and intermittent neutropenia. We have refined the critical region on chromosome 8q22 by haplotype analysis, and we report the characterization of a novel gene, COH1, that is mutated in patients with Cohen syndrome. The longest transcript (14,093 bp) is widely expressed and is transcribed from 62 exons that span a genomic region of approximately 864 kb. COH1 encodes a putative transmembrane protein of 4,022 amino acids, with a complex domain structure. Homology to the Saccharomyces cerevisiae VPS13 protein suggests a role for COH1 in vesicle-mediated sorting and transport of proteins within the cell.
Mechanisms of myopia in Cohen syndrome mapped to chromosome 8q22.
PURPOSE: To analyze the mechanisms of myopia in Cohen syndrome (Mendelian Inheritance in Man [MIM] no. 216550). METHODS: A cross-sectional study of 22 Finnish patients (age range, 2-57 years) with Cohen syndrome, which maps to chromosome 8q22, was undertaken to record cycloplegic refraction, keratometry (corneal power and radius of curvature), biometry (anterior chamber depth [ACD], lens thickness [LT], axial [AL] and vitreal length [VL]), and Hoffer Q-modeled lens power. These components of refraction were correlated to age and spherical equivalent (SE) at the corneal plane. Contribution to total myopia of refractive (corneal and lenticular) and axial components was modeled by multiple linear regression and by estimating the effect of deviation from population mean values. RESULTS: The mean SE in patients with Cohen syndrome older than 10 years was -9.35 D; the mean cylinder power, +1.70 D; and the mean anisometropia, 0.53 D. Relative to the emmetropic eye of a young adult, the AL and VL (mean, 23.9 and 16.6 mm, respectively) and lens power (mean, 30.30 D) were higher in 74% and 93% of patients, respectively, and the ACD (mean, 2.5 mm) was smaller and the LT (mean, 4.9 mm) and corneal power (mean, 45.63 D) higher than average in all patients. Corneal power (r = 0.513, P = 0.021) increased with age, but AL and VL (P = 0.46 and 0.54, respectively) and lens power (P = 0.89) did not correlate with age. The lens power decreased with AL (r = -0.564, P = 0.029) and tended to increase with corneal power (r = 0.475, P = 0.074). Multiple linear regression identified AL and corneal power as independent predictors of SE. Based on deviation from population means, the lens power explained 55%, corneal power 23%, and AL 22% of total myopia. ACD decreased and LT increased markedly with age, rendering angle-closure glaucoma a possibility. CONCLUSIONS: Myopia in Cohen syndrome is mainly refractive in type and is due to high corneal and lenticular power, which is otherwise rare in young patients. It may be superimposed on axial myopia, probably related to polygenic factors that determine myopia in the general population. The refractive myopia in Cohen syndrome may result from dysgenesis and atrophy of the cornea, ciliary body, and iris, which in turn cause iridial and zonular laxity and spherophakia.