Identification of novel RP2 mutations in a subset of X-linked retinitis pigmentosa families and prediction of new domains.

X-linked Retinitis Pigmentosa (XLRP) shows a huge genetic heterogeneity with almost five distinct loci on the X chromosome. So far, only two XLRP genes have been identified, RPGR (or RP3) and RP2, being mutated in approximately 70% and 10% of the XLRP patients. Clinically there is no clearly significative difference between RP3 and RP2 phenotypes. In the attempt to assess the degree of involvement of the RP2 gene, we performed a complete mutation analysis in a cohort of patients and we identified five novel mutations in five different XLRP families. These mutations include three missense mutations, a splice site mutation, and a single base insertion, which, because of frameshift, anticipates a stop codon. Four mutations fall in RP2 exon 2 and one in exon 3. Evidence that such mutations are different from the 21 RP2 mutations described thus far suggests that a high mutation rate occurs at the RP2 locus, and that most mutations arise independently, without a founder effect. Our mutation analysis confirms the percentage of RP2 mutations detected so far in populations of different ethnic origin. In addition to novel mutations, we report here that a deeper sequence analysis of the RP2 product predicts, in addition to cofactor C homology domain, further putative functional domains, and that some novel mutations identify RP2 amino acid residues which are evolutionary conserved, hence possibly crucial to the RP2 function.

Mutation analysis of the RPGR gene reveals novel mutations in south European patients with X-linked retinitis pigmentosa.

The RPGR (retinitis pigmentosa GTPase regulator) gene has been shown to be mutated in 10-20% of patients with X-linked retinitis pigmentosa (XLRP), a severe form of inherited progressive retinal degeneration. A total of 29 different RPGR mutations have been identified in northern European and United States patients. We have performed mutation analysis of the RPGR gene in a cohort of 49 southern European males affected with XLRP. By multiplex SSCA and automatic direct sequencing of all 19 RPGR exons, seven different and novel mutations were identified in eight of the 49 families; these include three splice site mutations, two microdeletions, and two missense mutations. RNA analysis showed that the three splice site defects resulted in the generation of aberrant RPGR transcripts. Six of these mutations were detected in the conserved amino-terminal region of RPGR protein, containing tandem repeats homologous to the RCC1 protein, a guanine nucleotide-exchange factor for Ran-GTPase. Several exonic and intronic sequence variations were also detected. None of the RPGR mutations reported in other populations were identified in our series. Our results are consistent with the notions of heterogeneity and minority causation of XLRP by mutations in RPGR in Caucasian populations.

Autosomal recessive familial exudative vitreoretinopathy: evidence for genetic heterogeneity.

Two unrelated families with familial exudative vitreoretinopathy (FEVR) show apparent autosomal recessive inheritance rather than the previously reported autosomal dominant or X-linked recessive mode of inheritance. Compared with the other modes of inheritance, the inherited clinical features here include earlier onset (at birth) and a more severe progressive course.

The gene for mesomelic dysplasia Kantaputra type is mapped to chromosome 2q24-q32.

Mesomelic dysplasia Kantaputra type (MDK) (MIM *156232) is a new autosomal dominant skeletal dysplasia characterized by dwarfism, shortening of the forearms/lower-legs, carpal/tarsal synostosis, and dorsolateral foot deviation. We studied a Thai family in which 15 members in 3 generations were affected with MDK. With reference to the breakpoints of a balanced translocation [t(2;8)(q31;p21)] in patients from a previously reported Italian family with a skeletal dysplasia that appears similar to MDK, a linkage analysis was performed in the Thai family using 50 CA-repeat markers mapped to nearby regions (2q22-q34 and 8p24-p21) of the translocation breakpoints. The results clearly ruled out a linkage of MDK to marker loci at the 8p24-p21 region, whereas all nine affected members available for the study shared a haplotype at four loci (D2S2284, D2S326, D2S2188, and D2S2314) spanning about 22.7 cM in the 2q24-q32 region. The computer-assisted two-point linkage analysis revealed maximum logarithm of odds (lod) scores of 4.82, 4.21, 4.82, and 4.21 (theta = 0) at these loci, respectively. These data indicated that the MDK locus is in the vicinity of D2S2284 and D2S2188 loci that are most likely mapped to 2q24-q32.

Two novel mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene in X-linked retinitis pigmentosa (RP3). Mutations in brief no. 172. Online.

Recently a new gene called RPGR (retinitis pigmentosa GTPase regulator) was isolated in Xp21.1 and found to be mutated in patients with RP3 type X-linked retinitis pigmentosa. Two new mutations, the first a single base pair deletion and the other a two base pairs deletion, have been found in one Spanish and one Italian family.

Mutation in the nerve-specific 5'non-coding region of Cx32 gene and absence of specific mRNA in a CMTX1 Italian family. Mutations in brief no. 195. Online.

Charcot-Marie-Tooth type I demyelinating neuropathies are genetically heterogeneous disorders (chrmosome 17,1,X). There are at least three genes on X chromosome, the more frequently involved being Cx32 in Xq13.1. Cx32 encodes for connexin-32, a gap junction protein of 283 aminoacids. We report the results of molecular studies in a CMTX1 Italian family, in which the mutation, found in the 5'-UTR, resulted in an abnormal mRNA connexin-32 expression. Mutations in PMP22 and P0 genes were also excluded in this family. Cx32 gene analysis carried out by PCR-SSCP on family members genomic DNAs, running a 321 bp fragment spanning the TATA box, the trasciptional start site, and the non coding exon 1b, revealed a shift correlated with a transition from C to T at position 40 of exon 1b of the 12 affected members, while was not found in the controls. Then the RT PCR-SSCP on cDNA from two peripheral nerve biopsies of two heterozygous females of the family were sequenced showing only the wild-type alleles and suggesting that mutated mRNAs were too unstable to be detected. The result also suggests a regulating role of the 5'-UTR of Cx32 mRNA.

A further observation of corneal dystrophy and perceptive deafness in two siblings.

We studied two siblings with the rare association of corneal dystrophy and perceptive deafness (Harboyan syndrome). To our knowledge, this is the third description of this hereditary disorder. The results of the clinical, genetic, audiometric, and ocular examination of the two siblings and the type of inheritance, which agree with the previous description of the syndrome, are reported. Various hereditary syndromes associated with corneal dystrophy are reviewed.

Linkage of DFNB1 to non-syndromic neurosensory autosomal-recessive deafness in Mediterranean families.

Recent studies show a susceptibility locus (DFNB1) responsible for non-syndromic neurosensory autosomal-recessive deafness (NSRD) mapping to the pericentromeric region of chromosome 13q. In order to better understand the frequency with which DFNB1 is the gene for deafness in our patient population and the role of DFNB1 in Caucasians, we performed a genetic linkage study with four microsatellite markers linked to DFNB1 in a total of 48 independent Mediterranean families, of which 30 and 18 were of Italian and Spanish descent, respectively. A maximum two-point lod score of 7.28 was found with marker D13S115 at a recombination frequency of theta 0.1. Significant lod scores were also obtained for D13S143, D13S292 and D13S175. Genetic heterogeneity was confirmed using the HOMOG program which indicated absence of linkage to DFNB1 in approximately 21% of the sample. This study clearly demonstrates that DFNB1 plays an important role in 79% of Mediterranean families with NSRD. Furthermore, results from multipoint analysis predict that the DFNB1 gene maps between markers D13S175 and D13S115 which are separated by approximately 14.2 cM.

Simultaneous occurrence of tetrasomy 21 and trisomy 8 in a patient with early blastic metamorphosis of chronic myeloproliferative disorder.

We report an unusual hyperdiploid karyotype characterized by the simultaneous occurrence of tetrasomy 21 and trisomy 8 detected during early blastic evolution of a BCR-ABL-negative chronic myeloproliferative disorder. Blast cells from this patient showed a striking response to all-trans-retinoic acid (ATRA)-induced differentiation as evaluated by CD15 expression following in vitro exposure to this inducer. Our report represents the first description of such a composite karyotype in human hematologic malignancies.

A clinical, genetic and echocardiographic study of hypertrophic cardiomyopathy in a large family.

OBJECTIVES: To confirm recent reports on the incidence of human lymphocyte antigens (HLA) in familial hypertrophic cardiomyopathy and to better define the genetic patterns found in these patients. METHODS: A large family (31 members, 18M, 13F, age range 6-80 years) with a high incidence of hypertrophic cardiomyopathy was screened for HLA, dermatoglyphic patterns and blood subtyping. RESULTS: Our finding show variable expression of the disease and reduced penetrance. No linkage between the disease-causing gene and HLA loci could be demonstrated in the family. There was no specific haplotype which present in all affected individuals and missing in all controls. Haplotype A2 B18 was the most commonly encountered in affected individuals but was absent in IV 3 and present in a few controls. No linkage was found between the disease-responsible gene and the blood groups. Finally, no typical pattern emerged from the dermatoglyphic studies. CONCLUSION: The genetic assessment of this family, in agreement with other European studies, showed no clear correlation between hypertrophic cardiomyopathy and blood groups ABO, Rh, Lewis, Duffy and was unable to show atypical or unusual dermatoglyphic patterns.

CFC syndrome: report on three additional cases.

We describe three patients, originating from three different Italian localities, affected by the cardio-facio-cutaneous (CFC) syndrome. In addition to a varying degree of mental retardation, these patients present characteristics consisting of a peculiar face with bitemporal frontal constriction and other anomalies involving the eyes, nose, ears, hair, skin, and heart that are consistent with this diagnosis.

Neu-Laxova syndrome: pathological, radiological, and prenatal findings in a stillborn female.

We describe a case of Neu-Laxova syndrome in a stillborn female. She was born at 41 weeks of gestation to consanguineous Italian parents, who had had 2 previous stillborn offspring. Pathological, radiological, and prenatal studies are reported.

Prenatal ultrasound diagnosis of macroglossia in the Wiedemann-Beckwith syndrome.

We report the ultrasound prenatal diagnosis at the 30th week of macroglossia in two sibs with the Wiedemann-Beckwith syndrome; the syndrome was also present in their mother. A study of high resolution chromosomes did not show any anomaly.

A malformed girl with a de novo proximal 6q deletion.

An additional case of interstitial deletion of chromosome 6, the first with breakpoints in q12 and q14, is reported. The female infant was the malformed first child of young, healthy parents. A review of proximal 6q deletions is made.

Cytogenetic study of a cell line of human penile cancer.

A cell line of penile cancer from a 60-year-old Ugandan black patient has been studied by the authors. Transmission and scanning electron microscopy showed a large number of blebs and microvilli at cell surface; desmosomes were evident at TEM. Cytogenetic investigation (R-, C-, Nor-banding) showed the frequent presence of some markers: del(1p),del(1q),iso(3q),der(4),del(8p),11q+, t rob(13;14), 14p+, t rob(21;21). The epidemiology, geographical distribution, and aetiological role of human papilloma virus type 16 and herpes simplex type 2 are discussed.