Sayedul Haque

Mutations in orthologous genes in human spondyloepimetaphyseal dysplasia and the brachymorphic mouse

The osteochondrodysplasias are a genetically heterogeneous group of disorders affecting skeletal development, linear growth and the maintenance of cartilage and bone. We have studied a large inbred Pakistani family with a distinct form of recessively inherited spondyloepimetaphyseal dysplasia (SEMD) and mapped a gene associated with this dwarfing condition to chromosome 10q23–24, a region syntenic with the locus for the brachymorphic mutation on mouse chromosome 19. We identified two orthologous genes, ATPSK2 and Atpsk2, encoding novel ATP sulfurylase/APS kinase orthologues in the respective regions of the human and mouse genomes. We characterized a nonsense mutation in ATPSK2 in the SEMD family and a missense mutation in the region of Atpsk2 encoding the APS kinase activity in the brachymorphic mouse. ATP sulfurylase/APS kinase catalyses the metabolic activation of inorganic sulfate to PAPS, the universal donor for post-translational protein sulfation in all cell types. The cartilage-specificity of the human and mouse phenotypes provides further evidence of the critical role of sulfate activation in the maturation of cartilage extracellular matrix molecules and the effect of defects in this process on the architecture of cartilage and skeletogenesis.

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 β 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.

A gene for universal congenital alopecia maps to chromosome 8p21-22.

Complete or partial congenital absence of hair (congenital alopecia) may occur either in isolation or with associated defects. The majority of families with isolated congenital alopecia has been reported to follow an autosomal-recessive mode of inheritance (MIM 203655). As yet, no gene has been linked to isolated congenital alopecia, nor has linkage been established to a specific region of the genome. In an attempt to map the gene for the autosomal recessive form of the disorder, we have performed genetic linkage analysis on a large inbred Pakistani family in which affected persons show complete absence of hair development (universal congenital alopecia). We have analyzed individuals of this family, using >175 microsatellite polymorphic markers of the human genome. A maximum LOD score of 7.90 at a recombination fraction of 0 has been obtained with locus D8S258. Haplotype analysis of recombination events localized the disease to a 15-cM region between marker loci D8S261 and D8S1771. We have thus mapped the gene for this hereditary form of isolated congenital alopecia to a locus on chromosome 8p21-22 (ALUNC [alopecia universalis congenitalis]). This will aid future identification of the responsible gene, which will be extremely useful for the understanding of the biochemistry of hair development.

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.

Distinct, autosomal recessive form of spondyloepimetaphyseal dysplasia segregating in an inbred Pakistani kindred.

We describe a large inbred kindred from a remote area of Pakistan, comprising eight generations, with a distinct form of spondyloepimetaphyseal dysplasia (SEMD). We evaluated 16 affected individuals: 11 males and 5 females. Analysis of the pedigree strongly suggests autosomal recessive inheritance, and consanguineous loops could account for all the affected individuals being homozygous for the abnormal allele. The clinical findings included short stature evident at birth, short bowed lower limbs, mild brachydactyly, kyphoscoliosis, an abnormal gait, enlarged knee joints, precocious osteoarthropathy, and normal intelligence. Radiographs demonstrated delayed epiphyseal ossification at the hips and knees, platyspondyly with irregular end plates and narrowed joint spaces, diffuse, early osteoarthritic changes, primarily in the spine and hands, and mild brachydactyly. Mild metaphyseal abnormalities were seen predominantly at hips and knees. This distinctive phenotype is distinct from other autosomal recessive forms of SEMD because of the mild degree of metaphyseal involvement, the type of brachydactyly, and the absence of loose joints or other clinical findings.

X-Chromosomally inherited split-hand/split-foot anomaly in a Pakistani kindred

SummaryA Pakistani kindred comprising seven generations and 36 members with the split-hand/split-foot anomaly is described. The full expression of the trait, monodactylous or split hand and split foot, mainly of the lobster-claw type, was present in 33 males and 3 females. Other females showed a distinctly milder expression of the trait, usually in the form of partial syndactyly, metacarpal and phalangeal hypoplasia, and malformation. The distribution of the affected members in the pedigree is compatible with X-chromosomal inheritance. Hemizygous males and presumably homozygous females exhibit the typical split-hand/split-foot anomaly, whereas only a part of the obligatory heterozygous females show the milder expression. There were no associated anomalies, such as ectodermal dysplasia, cleft lip/palate, macular degeneration, malformations of the long bones or internal organs, and overt mental retardation.

A locus for hereditary hypotrichosis localized to human chromosome 18q21.1.

Hereditary hypotrichosis is a rare autosomal recessive condition characterized clinically by alopecia. Three consanguineous kindreds with multiple affected individuals were ascertained from different regions of Pakistan. A novel hypotrichosis locus was mapped to a 5.5 cM region on chromosome 18q21.1. A maximum two-point LOD score of 5.25 was obtained at marker D18S36 (θ=0.0). Three genes each for desmoglein and desmocollin proteins are located in this region. The expression in epidermal desmosomes and their connection to the keratin intermediate filaments make these genes excellent candidates for recessive hypotrichosis.

A novel locus for autosomal recessive form of hypotrichosis maps to chromosome 3q26.33–q27.3

Genetic conditions affecting hair structure or the hair growth cycle may be isolated or they may occur as part of complex syndromes with associated abnormalities of other ectodermal appendages. Defective hair structure caused by mutations in key hair structural proteins can result in severe alopecia. The best characterised conditions at the molecular level in this category are monilethrix1 (MIM 158000) and Netherton syndrome2,3 (MIM 256500). Monilethrix is an autosomal dominant disorder in which alopecia is the presenting manifestation; however, the degree of alopecia is variable between patients and during different time periods for the same individual. Causative mutations have been identified in the keratin hair basic 6 gene (HB6, MIM 601928) and the keratin hair basic 1 gene (HB1, MIM 602153).4 Netherton syndrome is a rare autosomal recessive condition characterised by “bamboo hair” (trichorrhexis invaginata), congenital ichthyosiform erythroderma, and atopic diathesis. Serine protease inhibitor, Kazal-type 5 gene (SPINK5, MIM 605010), located on chromosome 5q31–q32, encodes a 15 domain serine protease inhibitor and is mutated in Netherton syndrome.3 Structural hair shaft defects are also a feature of Menkes kinky hair syndrome (MIM 309400). Menkes disease,5 with X linked inheritance, is caused by mutations in the gene encoding Cu2+ transporting ATPase, ATP7A (MIM 300011).6 Isolated forms of alopecia include congenital atrichia and different forms of hypotrichosis, which may represent a dysregulation of the hair growth cycle and remodelling.7 Autosomal recessive congenital atrichia (MIM 203655) is the most extreme example of hair loss. In affected individuals with this form of alopecia, hair is typically absent from the scalp with shedding shortly after birth. Congenital atrichia has been linked to 8p21, where several mutations of the hairless gene (HR, MIM 602302) have been reported as the underlying cause of congenital atrichia.8,9 Marie Unna …

A novel autosomal recessive non-syndromic deafness locus (DFNB35) maps to 14q24.1–14q24.3 in large consanguineous kindred from Pakistan

Autosomal recessive nonsyndromic deafness is one of the most frequent forms of inherited hearing impairment. Over 30 autosomal recessive nonsyndromic hearing loss loci have been mapped, and 15 genes have been isolated. Of the over 30 reported autosomal recessive nonsyndromic hearing loss (NSHL) loci, the typical phenotype is prelingual non-progressive severe to profound hearing loss with the exception of DFNB8, which displays postlingual onset and DFNB13, which is progressive. In this report we describe a large inbred kindred from a remote area of Pakistan, comprising six generations and segregating autosomal recessive nonsyndromic prelingual deafness. DNA samples from 24 individuals were used for genome wide screen and fine mapping. Linkage analysis indicates that in this family the NSHL locus, (DFNB35) maps to a 17.54 cM region on chromosome 14 flanked by markers D14S57 and D14S59. Examination of haplotypes reveals a region that is homozygous for 11.75 cM spanning between markers D14S588 and D14S59. A maximum two-point LOD score of 5.3 and multipoint LOD score of 7.6 was obtained at marker D14S53. The interval for DFNB35 does not overlap with the regions for DFNA9, DFNA23 or DFNB5.

Atrichia with papular lesions in two Pakistani consanguineous families resulting from mutations in the human hairless gene

Atrichia with papular lesions (APL) is a rare autosomal recessive form of total alopecia, characterized by hair loss soon after birth and the development of papular lesions of keratin-filled cysts over extensive areas of the body. Mutations in the hairless (hr) gene, a putative single zinc finger transcription factor, have been implicated in the pathogenesis of this disorder. In the present study, we describe two novel deletion mutations in exons 2 and 8 of the human hairless gene leading to frameshift and downstream premature termination codons in two consanguineous Pakistani families affected with atrichia.