X-linked Recessive Manner Research Articles

Genetic testing for congenital stationary night blindness

Abstract We studied the scientific literature and disease guidelines in order to summarize the clinical utility of the genetic test for congenital stationary night blindness (CSNB). CSNB is inherited in an autosomal dominant manner in the case of mutations in the GNAT1, PDE6B and RHO genes, in an autosomal recessive manner in the case of mutations in the CABP4, GNB3, GPR179, GRM6, LRIT3, SAG, SLC24A1, TRPM1 and genes and in an X-linked recessive manner in the case of mutations in the CACNA1F and NYX genes. The overall prevalence of CSNB is not known. Clinical diagnosis is based on clinical findings, ophthalmological examination, visual evoked potentials and electroretinography. The genetic test is useful for confirming diagnosis and for differential diagnosis, couple risk assessment and access to clinical trials.

Genetic characterization and disease mechanism of retinitis pigmentosa; current scenario.

Retinitis pigmentosa is a group of genetically transmitted disorders affecting 1 in 3000-8000 individual people worldwide ultimately affecting the quality of life. Retinitis pigmentosa is characterized as a heterogeneous genetic disorder which leads by progressive devolution of the retina leading to a progressive visual loss. It can occur in syndromic (with Usher syndrome and Bardet-Biedl syndrome) as well as non-syndromic nature. The mode of inheritance can be X-linked, autosomal dominant or autosomal recessive manner. To date 58 genes have been reported to associate with retinitis pigmentosa most of them are either expressed in photoreceptors or the retinal pigment epithelium. This review focuses on the disease mechanisms and genetics of retinitis pigmentosa. As retinitis pigmentosa is tremendously heterogeneous disorder expressing a multiplicity of mutations; different variations in the same gene might induce different disorders. In recent years, latest technologies including whole-exome sequencing contributing effectively to uncover the hidden genesis of retinitis pigmentosa by reporting new genetic mutations. In future, these advancements will help in better understanding the genotype-phenotype correlations of disease and likely to develop new therapies.

Whole-exome analysis of a Li-Fraumeni family trio with a novel TP53 PRD mutation and anticipation profile.

Li-Fraumeni syndrome is a clinically heterogeneous familial cancer predisposition syndrome with autosomal-dominant inheritance caused by heterozygous germline mutations in the TP53 gene. We here analyze the genetic background of a family with a 4-year-proband presented with a Li-Fraumeni tumor. The mother developed breast cancer at age 37 and the proband died at age 8. We performed Sanger sequencing and whole-exome sequencing on peripheral blood DNA from proband and relatives. Data analysis selected only high-quality score and depth reads, rare variants and protein impact involving missense, non-sense, frameshift and splice disrupt mutations. Disease implicated variants and predicted deleterious alterations were also chosen. TP53 genetic testing revealed a never reported TP53 deletion arose as de novo mutation in the mother and inherited by the proband. We then performed whole-exome analysis of the trio to uncover inherited variants from the father that potentially worsen the already altered genetic background in the proband. No pathogenic variants were inherited in autosomal recessive, de novo dominant or X-linked recessive manner. Comparing proband and father exome we detected 25 predicted deleterious variants including a nonsense mutation in ERCC3. Those inherited mutations are possible candidate modifiers linked to TP53, explaining the proband accelerated tumor onset compared to the mother and providing a possible explanation of the genetic anticipation event in this Li-Fraumeni family.

Aspects génétiques et moléculaires des dystrophinopathies

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are caused by mutations in the DMD gene that encodes the cytoskeletal protein, dystrophin. Dystrophinopathies are inherited in an X-linked recessive manner. Due to the tremendous size of the gene (2.2 megabases), the DMD locus has a high spontaneous mutation rate, and one third of sporadic cases of DMD are due to a de novo mutation. There are seven tissue-specific promoters in the gene. The skeletal muscular transcript contains 79 exons and encode the full-length protein (427-kDa) located at the inner face of the sarcolemma of muscle fibers. DMD gene mutations are highly heterogeneous. Large rearrangements (deletions or duplications of one or more exons) are most frequently involved while point mutations account for 20 %-30 % of cases. A survey of current strategies of molecular diagnosis is presented here. In particular, the role of muscle biopsy (for dystrophin and RNA analyses) in the diagnosis of dystrophinopathies is discussed. In more than 90 % of cases, the clinical severity is correlated with the impact of the mutations on the reading frame and the expression of the dystrophin (absence or residual amount of mutated protein). Various mechanisms contribute to the exceptions. Besides the clinical interest for the patient, the identification of the mutation allows accurate genetic counseling in the familles, and is a necessary prerequisite for the inclusion of the patient in the genotype-based clinical trials.

Genetic counselling of a male patient with hypohidrotic ectodermal dysplasia

Hypohidrotic ectodermal dysplasias (HED) are characterized by abnormal morphogenesis of epidermis and epidermal appendages. They may be inherited in an autosomal dominant, autosomal recessive or X-linked recessive manner. The most common type shows X-linked inheritance, and males.are usually more severely affected than females. In a male infant who was treated in our department, the diagnosis of HED was made 28 years ago. His mother and grandmother also show typical signs of HED in a milder form, while the other family members are all healthy. This young man wanted to know his risk of having affected children. We examined the segregation of X-chromosomes in ten members of the family with 2 intragenic and one extragenic short tandem repeat (STR) markers of the gene EDA (Xq12-13). According to our results, only family members with clinical signs of HED had the same X-chromosome (the affected son, his mother and grandmother), but none of the healthy family members. Direct mutation analysis of EDA was performed, but no aberration could be detected in this gene. Nevertheless, genetic counselling was possible based on the results of the segregation analysis. In this situation, the male progeny of the patient will not be affected, while female progeny will be carriers.

Colour vision deficiency

Colour vision deficiency is one of the commonest disorders of vision and can be divided into congenital and acquired forms. Congenital colour vision deficiency affects as many as 8% of males and 0.5% of females--the difference in prevalence reflects the fact that the commonest forms of congenital colour vision deficiency are inherited in an X-linked recessive manner. Until relatively recently, our understanding of the pathophysiological basis of colour vision deficiency largely rested on behavioural data; however, modern molecular genetic techniques have helped to elucidate its mechanisms. The current management of congenital colour vision deficiency lies chiefly in appropriate counselling (including career counselling). Although visual aids may be of benefit to those with colour vision deficiency when performing certain tasks, the evidence suggests that they do not enable wearers to obtain normal colour discrimination. In the future, gene therapy remains a possibility, with animal models demonstrating amelioration following treatment.

Mutations in the EDA gene are responsible for X‐linked hypohidrotic ectodermal dysplasia and hypodontia in Chinese kindreds

X-linked hypohidrotic ectodermal dysplasia (XLHED, OMIM 305100) is a rare congenital disorder that results in the defective development of teeth, hair, nails, and eccrine sweat glands. Previous studies found that mutations in the ectodysplasin A (EDA) gene are associated with XLHED. In the present study, we investigated four Chinese families suffering from classical XLHED and investigated two additional families segregating hypodontia in an X-linked recessive manner. Mutations were characterized respectively in the EDA gene in all families, and five of these mutations were found to be novel. Among these mutations, five were missense (c.200A>T, c.463C>T, c.758T>C, c.926T>G, and c.491A>C) and located in the functional domain of EDA, and one was a splice donor site mutation in intron 5 (c.IVS5 + 1G>A), which may result in an alternative transcript derived from a new cryptic splice site. Our data further confirm that EDA mutations could cause both XLHED and isolated hypodontia and provide evidence that EDA is a strong candidate gene for tooth genesis.

Correlation between Clinical Phenotypes and X-inactivation Patterns in Six Female Carriers with Heterozygote Vasopressin Type 2 Receptor Gene Mutations

About 90% of patients with congenital nephrogenic diabetes insipidus (NDI) have vasopressin type 2 receptor (V2R) gene mutations that are inherited in an X-linked recessive manner. Although most female carriers are asymptomatic, some female carriers show polydipsia and polyuria. The reason why female carriers show NDI symptoms is explained by skewed X-inactivation. We studied X-inactivation patterns of six female carriers with heterozygote V2R gene mutations. The X-inactivation pattern in peripheral blood leukocytes was examined using methylation analysis of the polymorphic CAG repeat in the androgen receptor gene. Two asymptomatic female carriers showed random X-inactivation (61.9% and 60.7%). Skewed X-inactivation patterns (71.6%, 79.4%, and 91.2%) occurring preferentially to normal X alleles were recognized in three female carriers who showed clinical NDI symptoms. However, in one female carrier who showed clinical NDI symptoms, random X-inactivation (55.4%) was recognized. In conclusion, the clinical NDI phenotypes may correlate with the X-inactivation patterns in female carriers with heterozygote V2R gene mutations. However, in some female carriers, we cannot predict the clinical phenotypes by the evaluation of the X-inactivation patterns in peripheral blood leukocytes, because X-inactivation ratios within an individual are sometimes different between tissues.

Mutations in PRPS1, Which Encodes the Phosphoribosyl Pyrophosphate Synthetase Enzyme Critical for Nucleotide Biosynthesis, Cause Hereditary Peripheral Neuropathy with Hearing Loss and Optic Neuropathy (CMTX5)

We have identified missense mutations at conserved amino acids in the PRPS1 gene on Xq22.3 in two families with a syndromic form of inherited peripheral neuropathy, one of Asian and one of European descent. The disease is inherited in an X-linked recessive manner, and the affected male patients invariably develop sensorineural hearing loss of prelingual type followed by gating disturbance and visual loss. The family of European descent was reported in 1967 as having Rosenberg-Chutorian syndrome, and recently a Korean family with the same symptom triad was identified with a novel disease locus CMTX5 on the chromosome band Xq21.32-q24. PRPS1 (phosphoribosyl pyrophosphate synthetase 1) is an isoform of the PRPS gene family and is ubiquitously expressed in human tissues, including cochlea. The enzyme mediates the biochemical step critical for purine metabolism and nucleotide biosynthesis. The mutations identified were E43D, in patients with Rosenberg-Chutorian syndrome, and M115T, in the Korean patients with CMTX5. We also showed decreased enzyme activity in patients with M115T. PRPS1 is the first CMT gene that encodes a metabolic enzyme, shedding a new light on the understanding of peripheral nerve-specific metabolism and also suggesting the potential of PRPS1 as a target for drugs in prevention and treatment of peripheral neuropathy by antimetabolite therapy.

Novel mutations underlying nephrogenic diabetes insipidus in Arab families

PurposeNephrogenic Diabetes Insipidus (NDI) is genetically heterogeneous and may be inherited in an X-linked or autosomal recessive manner. We aimed to investigate the molecular basis of NDI among Arab families. MethodsDirect sequencing of coding regions for AQP2 and AVPR2 was used to identify underlying mutations. One large deletion required Southern blot analysis and a PCR-based strategy to identify deletion junctions. ResultsWe identified two novel missense mutations (AQP2:p.Gly100Arg and p.Gly180Ser) in AQP2 and one novel missense mutation (AVPR2:p.Gly122Asp), one previously reported missense mutation (AVPR2:p.Arg137His) and one novel contiguous deletion (AVPR2:c.25 + 273_ARHGAP4o:2650-420del) affecting AVPR2. We also describe evidence of lyonization associated with the novel deletion. ConclusionsTwo novel mutations were identified in each of AVPR2 and AQP2 underlying CNDI in Arab families. Identification of these mutations will facilitate early diagnosis of CNDI, counseling of families and provide opportunities for early intervention aimed at reducing morbidity. The presence of affected females and consanguinity, as is often observed in Arab communities should not be used to rule out AVPR2 as a candidate when considering diagnostic testing. Careful observation of phenotypic heterogeneity should be used in referring such families for both AQP2 and AVPR2 molecular genetic testing.

Mucopolysaccharidosis type II in females: Case report and review of literature

Mucopolysaccharidosis type II (Hunter disease, iduronate-2-sulfatase deficiency) was diagnosed in a 4-year-old female by demonstrating low iduronate-2-sulfatase activity both in leukocytes and fibroblasts and by the presence of a novel, complex rearrangement of the iduronate-2-sulfatase gene in heterozygous form. Mucopolysaccharidosis type II is inherited in an X-linked recessive manner and consequently females are rare. The disease phenotype in this case is due to complete unilateral inactivation of the nonmutant paternal X chromosome of the patient. The case presented here underscores the fact that a diagnosis of mucopolysaccharidosis type II should be suspected in any female who presents with the relevant clinical symptoms.

Androgen Insensitivity Syndrome: Somatic Mosaicism of the Androgen Receptor in Seven Families and Consequences for Sex Assignment and Genetic Counseling

Androgen insensitivity syndrome (AIS) is caused by numerous mutations of the androgen receptor (AR) gene. The phenotype may range from partial AIS (PAIS) with ambiguous genitalia to complete AIS (CAIS) with female genitalia. In 70% of the cases, AR mutations are transmitted in an X-linked recessive manner through the carrier mothers, but in 30%, the mutations arise de novo. When de novo mutations occur after the zygotic stage, they result in somatic mosaicisms, which are an important consideration for both virilization in later life-because both mutant and wild-type receptors are expressed-and genetic counseling. We report here six patients with AIS due to somatic mutations of the AR and one mother with somatic mosaicism who transmitted the mutation twice. Of the four patients with PAIS, three presented spontaneous or induced virilization at birth or puberty. These cases underline the crucial role of the remnant wild-type AR for virilization because the same mutations, when they are inherited, lead to CAIS. We also report two novel mutations of the AR, with somatic mosaicism, detected in patients with CAIS. Thus, the remnant wild-type receptor does not always lead to virilization. In one of these patients, a high ratio of wild-type to mutant AR expression was found in the gonads and genital skin fibroblasts. Although no prenatal virilization occurred, the possibility of virilization at puberty could not be excluded, and early gonadectomy was performed. A seventh patient had a CAIS with a novel germline AR mutation. The mutation was inherited from the mother, in whom mosaicism was detected in blood and who transmitted the mutation to a second, XX, offspring. The detection of somatic AR mutations is particularly important for the clinical management and genetic counseling of patients with AIS. Before definite sex assignment, a testosterone treatment trial should be performed in all patients with PAIS, but it becomes crucial when an AR mosaicism has been detected. In patients with CAIS or severe PAIS raised as female, there is no consensus about when (early childhood or puberty) gonadectomy should be performed. When somatic AR mutations are detected, however, gonadectomy should be performed earlier because of the risk of virilization during puberty. When a germline de novo mutation is identified in the index case, the risk of transmission to a second child due to a possible germ cell mosaicism in the mother cannot be excluded. However, given the high number of AR de novo mutations and the rarity of such reports, this risk appears to be very low.

PENOSCROTAL TRANSPOSITION: REVIEW OF 53 PATIENTS

Penoscrotal transposition is a rare congenital abnormality of the external genitalia. We determine whether there is a genetic basis for this disorder, define the incidence of coexisting organ system anomalies, and compare the results of surgical techniques to correct transposition and hypospadias. We report the largest, single institution series of 53 patients 1 day to 30 years old with penoscrotal transposition. Of the patients 13% had a family history of penoscrotal transposition. Interestingly, we identified 1 family in which inheritance occurred in an X-linked recessive manner. There were 17 (32%) patients who had abnormalities in other organ systems, with the genitourinary system in 9 affected most. A total of 79% of patients had hypospadias and 81% chordee. These anomalies were corrected with a single stage Thiersch-Duplay urethroplasty in 6 patients and complex repair with bladder or buccal mucosa, or a staged procedure in 34. Complication rates for urethroplasty were similar. Correction of the transposition included a Glenn-Anderson technique in 37 patients, Singapore rotational flaps in 7 and V-Y procedure in 6. The Glenn-Anderson repair produced the best cosmetic results and was associated with a significantly lower incidence of complications (p = 0.001). We identified a subgroup of patients with a family history of penoscrotal transposition. Treatment requires an awareness of the association with other organ system anomalies. The Glenn-Anderson technique was the most successful method to correct transposition. Most patients required release of chordee and complex urethroplasty for hypospadias.

Nonrandom selection of hair follicles in HPRT heterozygosity.

The gene for hypoxanthine phosphoribosyltransferase (HPRT) has been mapped to the X chromosome, and HPRT-deficiency syndromes are inherited in an X-linked recessive manner.1 Two populations of cells can be demonstrated in the female heterozygous carriers of these syndromes. While great strides have been made in the detection of point mutations in cDNA, these methods are not yet sufficiently reliable for routine detection of heterozygotes.2 At present, biochemical methods which detect HPRT+ and HPRT− populations of cells are both technically simpler and more reliable. Cultured fibroblasts, lymphocytes, and hair roots have been used for this purpose.1 Of these three, we have found the hair root method to be the least invasive, fastest, and most reliable.3 In the past 15 years we have detected a total of 94 heterozygous carriers of HPRT-deficiency syndromes by this method.

Carrier state in HGPRT deficiency. A study in 14 Spanish families.

HGPRT deficiency is inherited in a chromosome X-linked recessive manner (1). Most of heterozygous females are asymtomatic and have normal serum urate concentrations (2). Moreover, HGPRT activity in hemolysate from HGPRT deficient carrier females is usually in the normal range (3). A number of methodologies have been designed for carrier testing in HGPRT deficient families, HGPRT activity in hair follicles, selective medium cultured skin fibroblasts and genetic analysis, being the most widely used. The purpose of this study was to review our experience with carrier diagnoses in 14 Spanish families with HGPRT deficiency by means of enzymatic and genetic tests.KeywordsGenetic TestingHair FollicleFemale FetusCarrier TestingHeterozygous FemaleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nonrandom selection of hair follicles in HPRT heterozygosity

The gene for hypoxanthine phosphoribosyltransferase (HPRT) has been mapped to the X chromosome, and HPRT-deficiency syndromes are inherited in an X-linked recessive manner.1 Two populations of cells can be demonstrated in the female heterozygous carriers of these syndromes. While great strides have been made in the detection of point mutations in cDNA, these methods are not yet sufficiently reliable for routine detection of heterozygotes.2 At present, biochemical methods which detect HPRT+ and HPRT− populations of cells are both technically simpler and more reliable. Cultured fibroblasts, lymphocytes, and hair roots have been used for this purpose.1 Of these three, we have found the hair root method to be the least invasive, fastest, and most reliable.3 In the past 15 years we have detected a total of 94 heterozygous carriers of HPRT-deficiency syndromes by this method.

Carrier state in HGPRT deficiency: A study in 14 Spanish families

HGPRT deficiency is inherited in a chromosome X-linked recessive manner (1). Most of heterozygous females are asymtomatic and have normal serum urate concentrations (2). Moreover, HGPRT activity in hemolysate from HGPRT deficient carrier females is usually in the normal range (3). A number of methodologies have been designed for carrier testing in HGPRT deficient families, HGPRT activity in hair follicles, selective medium cultured skin fibroblasts and genetic analysis, being the most widely used. The purpose of this study was to review our experience with carrier diagnoses in 14 Spanish families with HGPRT deficiency by means of enzymatic and genetic tests.

Proposed cause of marked vasopressin resistance in a female with an X-linked recessive V2 receptor abnormality.

Almost all cases of congenital nephrogenic diabetes insipidus (NDI) are transmitted in an X-linked recessive manner by an asymptomatic carrier female to her affected son. Severe symptomatic NDI has not previously been reported in a female with X-linked recessive NDI. Each of the three members of this family has an abnormal V2 receptor gene, which results in truncation of the V2 receptor beginning at arginine-337. This prematurely terminates the receptor at the carboxy-terminal tail and very likely disrupts receptor function. The son has an abnormal V2 receptor gene on his X-chromosome, whereas the mother and daughter have one normal and one abnormal gene for the V2 receptor. The infusion of desmopressin into the mother and son reveals a total lack of antidiuretic response, whereas the daughter increases urinary osmolality normally. The plasma factor VIII concentration after the infusion of desmopressin in the son does not rise, whereas the mother and daughter have half of the normal factor VIII response, similar to asymptomatic female carriers of NDI. These responses to desmopressin in daughter and son are those of a typical carrier female and male affected with NDI. In contrast, the mother acts as an NDI patient when the urine concentration is measured, but acts as a carrier in terms of the factor VIII response to desmopressin. We postulate that the renal tubular cells of the mother demonstrate extreme lyonization of X-chromosome inactivation, whereas in the tissue that subserves the hematological response to desmopressin, X-chromosome inactivation followed a more typically random distribution.

Familial hydrocephalus with a low-insertion umbilicus

Two brothers, age 16 months and 3 years, had a seemingly unique combination of hydrocephalus of the lateral ventricles and a low-insertion umbilicus. Both had similar mildly unusual facies and inguinal hernias; one had unilateral cryptorchidism. The older brother had tetralogy of Fallot, and the younger had mildly enlarged, echogenic kidneys with vesicoureteral reflux. Neither boy had adducted thumbs, pyramidal tract signs, or significant developmental delay. A review of the literature on familial hydrocephalus found no similar cases. A low-set umbilicus is not a frequently noted anomaly; its embryology and associated syndromes are discussed. The association of hydrocephalus and a low-set umbilicus appears to be the manifestation of a monogenic disorder in this family, and could be inherited in either an autosomal recessive or X-linked recessive manner.

New multisystemic disorder involving heart valves, skin, bones, and joints in two brothers

We report on 2 brothers with a severe progressive disorder characterized by thick skin, acne conglobata, "coarse" face, osteolysis, gingival hypertrophy, brachydactyly, camptodactyly, and mitral valve prolapse. The youngest brother died at age 24 years because of heart failure. Biochemical and pathological studies excluded known metabolic diseases. We think that this is a new genetic disorder inherited in autosomal recessive or X-linked recessive manner.