Molecular Genetic Studies And Genotype-phenotype Relationship Studies Of Two Monogenic Disorders

Monogenic disorder is the result of a single mutated gene. According to the inheritance patterns, it can be classified into two groups—Mendel inherited diseases and non-Mendel inherited diseases. The former includes autosomal inheritance, X-linked inheritance and Y-linked inheritance while the latter includes mitochondrial diseases and imprinted gene diseases. To identify the pathogenic genes and study the molecular mechanism of monogenic disorder as well as the genotype-phenotype relationship, we perform clinical investigation and mutational screening on one Chinese family with X-linked recessive ocular albinism and two unrelated Chinese families with Marfan syndrome.X-linked recessive ocular albinism is a monogenic disease due to the mutation of G PROTEIN-COUPLED RECEPTOR 143 gene(GPR143). This gene encodes a G-protein-coupled receptor. The patients usually have severely impaired visual acuity, marked photophobia, and variable strabismus. Interestingly, this form of albinism particularly affects the eyes, and the pigmentation of hair and skin is usually normal. In 1st chapter, we report a Chinese family with X-linked recessive ocular albinism in which a novel missense mutation in the GPR143 was observed. The boy exhibited particularly mild hypopigmentation in the fundus and nystagmus that appeared at 4 months of age. Clinical examinations at 7 months of age revealed hypopigmentation of the fundus and foveal hypoplasia. The hypopigmentation was mild and the pigmentation of the iris was normal compared with other Chinese irises. In the mother, foveal hypoplasia and characteristic alternating hyperpigmented and hypopigmented peripheral streaks at the level of the retinal pigment epithelium were observed. No abnormalities were observed in the father or his aunt. Genomic DNA was extracted from peripheral blood leucocytes. Sanger sequencing on PCR products covering all exons and intron-exon boundaries in both directions was employed to detect mutations in the gene. The novel missense mutation, c.494C>A(p.Ala165Asp), in GPR143 was identified in both the boy and his mother. The mutation was absent in his father and in 50 unrelated normal control subjects. Our study has expanded the mutational spectrum of GPR143, and made effort of uncovering the phenotype-genotype relationship in Chinese group of ocular albinism. Also, our result has provided the evidence for early diagnosis and early treatment of the ocular albinism patients as well as for the prenatal diagnosis when the patient's parents are preparing for having a baby; and benefit the further research of Chinese group of the ocular albinism.Marfan syndrome is a autosomal-dominant and multisystem disorder, due to the mutations of FBN1. This gene encodes fibrillin-1. The cardinal clinical features of patients are arachnodactyly, scoliosis, dilatation of the aortic root and ectopia lenti et.al.. In 2nd chapter, we performed clinical and genetic investigation in 2 unrelated Chinese families. Family 1 had 1 patient with cardiac problem and the other family had 2 patients, one died, the other with breathing and cardiac problems. Next generation sequencing of FBN1 were performed in the patient of family 1 and Sanger sequencing of the detected pathogenic mutation from NGS was performed in all members. Sanger sequencing covering all the exons and intron-exon boundaries were performed in the patient and the parents in family 2. Bioinformatics analyses were engaged in the variations unraveled. Fifty healthy individuals were also investigated in the same manner. Finally, both patients were diagnosed with Marfan syndrome. A novel mutation c.4685G>A(p.Cys1562Tyr)was detected in the patient of family 1 but was absent in his parents and the unaffected sister. This is a previously unreported novel mutation. Meanwhile, we detected the mutation c.3706T>C(p.Cys1236Arg) in the patient of family 2. It was absent in the unaffected parents, therefore it was a de novo mutations too. This mutation has been previously reported and known to be associated with neonatal Marfan syndrome. Both mutations were absent in the 50 healthy controls. Our study report 2 de novo mutations in 2 Chinese families and discuss the phenotype-genotype relationship. One of the 2 mutations is novel. The phenotypes of the mutation c.4685G>A(p.Cys1562Tyr)was associated with classical Marfan syndrome in family 1, but the c.3706T>C(p.Cys1236Arg) was with neonatal type of Marfan syndrome in family 2. De novo mutations may be a cause for a proportion of mutations underlie the disease.Our study has successfully come out with the molecular diagnoses of two monogenic disorders, expanded the spectrums of the causal genes; has done research on the genotype-phenotype relationship; and has indicated the significance of the early molecular diagnosis on early treatment and prenatal diagnosis.