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Genetics and metabolic disorders
Published in Jagdish M. Gupta, John Beveridge, MCQs in Paediatrics, 2020
Jagdish M. Gupta, John Beveridge
The condition is Duchenne muscular dystrophy which is X-linked recessive in its inheritance. Julie is an obligate carrier by pedigree analysis alone. Julie's sister has an a priori carrier risk of 1 in 2, but with each unaffected son she produces it becomes less and less likely that she is a carrier. A repeatedly elevated CK will confirm carrier status but a normal CK does not eliminate carrier status as many carriers have normal CK levels. Once the underlying mutation is known, prenatal diagnosis can be offered to ail possible carriers in the family.
SBA Answers
Published in Justin C. Konje, Complete Revision Guide for MRCOG Part 2, 2019
C Her father is affected or she has an affected son and an affected relative in the maternal lineA woman is considered an obligate carrier for haemophilia A or B, if her father has haemophilia or she has an affected son and an affected relative(s) in the maternal line. (Management of InheritedBleeding Disorders in Pregnancy. The Royal College of Obstetricians and Gynaecologists Green-top Guideline No. 71, April 2017)
Neuromuscular disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
The general problems of calculating risks for a lethal X-linked disorder are discussed in Chapters 2 and 7. A woman with an affected son and another affected close male relative (e.g. brother or maternal uncle) is an obligate carrier, with a 50% risk of further sons being affected and of daughters being carriers. A woman with two affected sons should be given similar advice, although she may be mosaic rather than a full constitutional carrier of the condition. Detailed examples of risk estimation in DMD can be found in Chapter 2 and in the books of Young and Emery (see Appendix 1).
GPR143 genotypic and ocular phenotypic characterisation in a Chinese cohort with ocular albinism
Published in Ophthalmic Genetics, 2021
Junwei Zhong, Bing You, Ke Xu, Xiaohui Zhang, Yue Xie, Yang Li
One of the limitations of this study was its retrospective design and the lack of longitudinal observation. One previous study found that pigmentation of the iris and the retina increased with advancing age, resulting in a decreased photophobia, less nystagmus, and even an improvement in visual acuity (24). In the current study, we only observed two patients (one infant and one 3-year-old boy) and one 4-year-old obligate carrier who presented with more obvious hypopigmentation in their fundus. OCT scans of the 4-years-old carrier demonstrated a mild foveal hypoplasia, which could be divided into grade 1 based on the categorizing system described by Thomas et al (25). One previous study also observed this kind of mild foveal hypoplasia in six female carriers and conjectured that maturation of the inner retina may be the structure most sensitive to loss of melanin (26). We will follow up these patients and carriers in the future.
NYX-related Congenital Stationary Night Blindness in Two Siblings due to Probable Maternal Germline Mosaicism
Published in Ophthalmic Genetics, 2021
H. l. Scanga, A. Liasis, M. S. Pihlblad, K. K. Nischal
In this family, two male children with clinical and electrophysiologic evidence of cCSNB were hemizygous for a pathogenic, in-frame deletion of NYX notated c.339_353delTGAGCTGCGCCTGGC. This variant results in a loss of function consistent with other pathogenic variants of this gene and has been previously reported in association with cCSNB (5). Based on the X-linked recessive inheritance pattern of NYX, a mother of two affected males is presumed to be an obligate carrier for the pathogenic variant; however, in this family, maternal genetic testing of independent blood and saliva samples failed to detect the causative variant. Failure to identify the pathogenic variant in a mother of multiple affected children could have several explanations, including maternal mosaicism of the germline with or without somatic involvement, a de novo mutational event, technical or human error during sample collection and laboratory testing, or a non-biological relationship.
Phenotypic high myopia in X-linked retinitis pigmentosa secondary to a novel mutation in the RPGR gene
Published in Ophthalmic Genetics, 2019
Hortensia Sanchez Tocino, Cecilia Diez Montero, Ana Villanueva Gómez, Rosa Lobo Valentin, Javier Antonio Montero-Moreno
The direct sequencing of PCR products of the proband with RP revealed the hemyzygous status for a novel variant NM_0010344853.1 in the exon 3 of RPGR gene (c212C>G), which was confirmed by Sanger sequencing. This mis-splicing caused a substitution of the 71 amino acid C > G and the (p.Ser71*) was changed to stop codon possibly resulting in a truncated protein and/or a nonsense- mediated mRNA decay. Both the proband’s mother (obligate carrier) and the other three female carriers with degenerative PM were found to be heterozygous for this RP-related variant. This mutation was neither observed in the asymptomatic unaffected members of this family.