Clinical and molecular findings of 13 families from Saudi Arabia and a family from Sudan with homocystinuria.

Homocystinuria due to cystathionine beta synthase (CBS) deficiency results in elevated plasma homocysteine and methionine levels, which are associated with multiple organ pathologies, including vascular, respiratory, musculoskeletal, nervous, and ocular tissues. This autosomal recessive disorder is caused by homozygous or compound heterozygous mutations in the CBS gene encoding for the CBS. Although homocystinuria is observed in Arab and North African patients, their clinical presentations have not been described and molecular causes remained largely uninvestigated. In this study, we describe the clinical presentations of 22 homocystinuria patients from 13 Saudi Arabian families and 1 North African Sudanese family. Cardinal biochemical features of homocystinuria manifested in all patients, but heterogeneity of expression was observed for other associated phenotypes. One patient developed Legg-Calvé-Perthes disease that has not been previously described in homocystinuria. In the Saudi families, a novel nonsense mutation, p.Trp323X, and recurrent p.Arg336Cys and p.Gly153Arg mutations were identified in the CBS gene. The p.Trp323X mutation was found in 10 of the 13 unrelated Saudi families. In the Sudanese family, the p.Thr257Met mutation in the CBS gene, previously described in Italian and Spanish patients, was found. This study shows that the spectrum of CBS gene mutations in Saudi homocystinuria patients is quite different than the Arab patients from Qatar and Israel. This study is the only detailed phenotypic and genetic depiction of homocystinuria patients from Saudi Arabia and Sudan. The data are useful for diagnosis and management of Saudi patients.

Novel and recurrent mutations in the AIRE gene of autoimmune polyendocrinopathy syndrome type 1 (APS1) patients.

Autoimmune polyendocrinopathy syndrome type 1 (APS1) is characterized by the presence of at least two out of three clinical features, which include Addison's disease, hypoparathyroidism, and chronic mucocutaneous candidiasis. This disorder is caused by mutations in the AIRE (autoimmune regulator) gene. While several AIRE mutations have been described in APS1 patients of various ethnic origins, the genetic cause of APS1 in Arab patients requires further investigation. This study describes seven Arab families, in which 18 patients had APS1. In addition to the cardinal features of APS1, some patients exhibited alopecia, diabetes mellitus, nephrocalcinosis and other phenotypes associated with APS1. DNA sequencing of the AIRE gene of patients from this study identified four novel and one recurrent mutation. These mutations likely result in loss of AIRE function in the patients. In addition, it was noted that the non-pathogenic c.834C> G mutation (rs1800520, encoding for p.Ser278Arg) occurs with high incidence in the AIRE gene of Arab individuals. Furthermore, this investigation demonstrates inflammation of the hair follicles in APS1 patients with alopecia universalis. We conclude that Arab APS1 patients carry novel and recurrent mutations in the AIRE gene.

A family exhibiting arterial tortuosity syndrome displays homozygosity for markers in the arterial tortuosity locus at chromosome 20q13.

Arterial tortuosity associated with hyperextensible skin and hypermobility of joints, features that are characteristics of Ehlers-Danlos syndrome (EDS), has been described in several families. An arterial tortuosity locus has recently been mapped to chromosome 20q13. Here, we report a consanguineous Kurdish family in which an affected child manifested elongation and severe tortuosity of the aorta, carotid, and other arteries. Additional clinical symptoms include loose skin, hypermobile joints, hernias, and facial features that resemble EDS individuals. To examine whether the arterial tortuosity locus was involved in this child, homozygosity analysis was performed using microsatellite markers on 20q13. The affected child was found homozygous, whereas the unaffected parents and three siblings were heterozygous. Additional typing defined the genomic interval to a 37-cm region within which the arterial tortuosity locus is located. Three functional candidate genes (B4GALT5, KCNB1, and PTGIS) were sequenced. No mutations were discovered in the coding regions of these three genes and the promoter regions of B4GALT5 and KCNB1 genes. Moreover, the B4GALT5 mRNA expression was unaltered in patient-derived lymphoblastoid cells. In the PTGIS gene promoter, the affected child was homozygous for eight variable number of tandem repeats, while parents and unaffected siblings carried six repeats.

Fine mapping of the X-linked split-hand/split-foot malformation (SHFM2) locus to a 5.1-Mb region on Xq26.3 and analysis of candidate genes.

Split-hand/split-foot malformation (SHFM) is a genetically heterogeneous disorder, with five known loci, that causes a lack of median digital rays, syndactyly, and aplasia or hypoplasia of the phalanges, metacarpals, and metatarsals. In the only known SHFM2 family, affected males and homozygous females exhibit monodactyly or bidactyly of the hands and lobster-claw feet. This family (1) was revisited to include additional subjects and genealogical data. All 39 affected males and three females fully expressed the SHFM, while 13 carrier females examined exhibited partial expression of SHFM. We narrowed the previously linked 22-Mb genetic interval on Xq24-q26 (2), by analyzing additional family members and typing additional markers. The results define a 5.1-Mb region with a new centromeric boundary at DXS1114 and a telomeric boundary at DXS1192. We did not identify mutations in the exons and exon/intron boundaries of 19 candidate genes. These data suggest that the mutation may lie in a regulatory region of one of these candidate genes or in another gene within the SHFM2 region with unclear role in limb development.

Novel mutations in the EXT1 gene in two consanguineous families affected with multiple hereditary exostoses (familial osteochondromatosis).

Multiple hereditary exostoses (HME) is an autosomal dominant developmental disorder exhibiting multiple osteocartilaginous bone tumors that generally arise near the ends of growing long bones. Here, we report two large consanguineous families from Pakistan, who display the typical features of HME. Affected individuals also show a previously unreported feature--bilateral overriding of single toes. Analysis using microsatellite markers for each of the known EXT loci, EXT1, EXT2, and EXT3 showed linkage to EXT1. In the first family, mutation analysis of the EXT1 gene revealed that affected individuals were heterozygous for an in-frame G-to-C transversion at the conserved splice donor site in intron 1. This mutation is predicted to disrupt splicing of the first intron and produce a frameshift that leads to a premature termination codon. In the second family, an insertion of an A in exon 8 is predicted to produce a frameshift at codon 555 followed by a premature termination, a further 10 codons downstream. In both families, an increased number of affected male subjects were observed. In affected females in family 2, phenotypic variability and incomplete penetrance were noted.

Mutation in the cartilage-derived morphogenetic protein-1 (CDMP1) gene in a kindred affected with fibular hypoplasia and complex brachydactyly (DuPan syndrome).

The present authors have previously described a consanguineous Pakistani family with fibular hypoplasia and complex brachydactyly (DuPan syndrome) inherited as an autosomal recessive trait. All affected individuals showed either reductions or absence of bones in the limbs, and appendicular bone dysmorphogenesis with unaffected axial bones. Obligate heterozygote parents were phenotypically normal. Mutations in the cartilage-derived morphogenetic protein 1 (CDMP1) gene have been reported in two acromesomelic chondrodysplasias (i.e. Hunter-Thompson type and Grebe type) which are phenotypically related to DuPan syndrome. CDMP1, a member of the transforming growth factor beta super-family of secreted signalling molecules, has been reported to regulate limb patterning and distal bone growth. Therefore, the present authors examined genomic DNA from the family with DuPan syndrome for mutations in the CDMP1 gene. Affected individuals were homozygous for a missense mutation, T1322C, in the coding region of the CDMP1 gene. This mutation was not found in 44 control subjects of Pakistani origin. The T1322C change predicts a leu441pro substitution in the mature domain of the CDMP1 protein. This is likely to cause a conformational change in the CDMP1 protein that influences the expression of genes which are required for normal bone development. This finding extends the spectrum of phenotypes produced by defects in the CDMP1 gene.