ABSTRACT
Predicting the pathogenicity of biallelic missense variants can be challenging. Here, we use a deficit of observed homozygous carriers of missense variants, versus an expected number in a set of 153,054 chip-genotyped Icelanders, to identify potentially pathogenic genotypes. We follow three missense variants with a complete deficit of homozygosity and find that their pathogenic effect in homozygous state ranges from severe childhood disease to early embryonic lethality. One of these variants is in CPSF3, a gene not previously linked to disease. From a set of clinically sequenced Icelanders, and by sequencing archival samples targeted through the Icelandic genealogy, we find four homozygous carriers. Additionally, we find two homozygous carriers of Mexican descent of another missense variant in CPSF3. All six homozygous carriers of missense variants in CPSF3 show severe intellectual disability, seizures, microcephaly, and abnormal muscle tone. Here, we show how the absence of certain homozygous genotypes from a large population set can elucidate causes of previously unexplained recessive diseases and early miscarriage.
Subject(s)
Cleavage And Polyadenylation Specificity Factor/genetics , Genetic Predisposition to Disease/genetics , Homozygote , Intellectual Disability/genetics , Mutation, Missense , Adolescent , Alleles , Child , Child, Preschool , Female , Gene Frequency , Genetics, Population/methods , Genotype , Humans , Iceland , Infant , Intellectual Disability/pathology , Male , Pedigree , Phenotype , Syndrome , Whole Genome Sequencing/methodsABSTRACT
PURPOSE: The Stokes-Einstein equation predicts that diffusion is inversely correlated with viscosity of the medium. This predicts that diffusion fluxes should be lower in vitreous humour than in saline solution with lower viscosity. We test this hypothesis, which has implications for vitrectomy. METHODS: Diffusion cells were used, with a middle chamber filled with saline solution with different concentrations of hyaluronic acid (0 microg/ml, 30 microg/ml, 90 microg/ml and 180 microg/ml) or porcine vitreous humour, between cellophane membranes. HPLC was used to measure the concentration of the diffusing molecule, dexamethasone, and calculate the flux through the chamber filled with the various media. The diffusion coefficients were calculated, using Fick's law. Viscosity was measured with a Brookfield digital DV-I+viscometer. RESULTS: The diffusion coefficient for dexamethasone in vitreous humour is 0.065 +/- 0.022 cm(2)/hour, 0.26 +/- 0.12 cm(2)/hour for saline alone, 0.17 +/- 0.04 cm(2)/hour for saline with 30 microg/ml hyaluronan, 0.076 +/- 0.009 cm(2)/hour with 90 microg/ml hyaluronan, and with 180 microg/ml hyaluronan 0.072 +/- 0.0018 cm(2)/hour (p < 0.001). The viscosity of liquid vitreous is 6.29 +/- 2.3 cp, and the viscosity of saline alone is 1.01 +/- 0.008 cp. For saline with 30 microg/ml of hyaluronan the viscosity is 1.04 +/- 0.015, with 90 microg/ml hyaluronan is 1.06 +/- 0.01, and with 180 microg/ml hyaluronan is 1.08 +/- 0.014 (p < 0.001). CONCLUSIONS: Dexamethasone diffuses four times faster through saline solution than vitreous humour. Liquid vitreous humour is about six times more viscous than saline. The results indicate that diffusion is faster in saline solution than in vitreous humour, in accordance to the Stokes-Einstein equation. This finding can help explain some of the physiological, pharmacological and clinical consequences of vitrectomy.
