Extended haplotype studies in South African and Dutch variegate porphyria families carrying the recurrent p.R59W mutation confirm a common ancestry.

BACKGROUND: Variegate porphyria (VP) is due to a partial deficiency of protoporphyrinogen oxidase (PPOX), the seventh enzyme in the haem biosynthetic pathway. Clinically, VP is characterized by photosensitivity and acute neurovisceral attacks that can manifest separately or together in affected individuals. The disease is inherited in an autosomal dominant fashion with incomplete penetrance and PPOX gene mutations associated with VP are usually unique to patients and their families. In South Africa, however, VP is highly prevalent as the result of a founder mutation, designated p.R59W. Previous genealogical and haplotype studies showed a link between South African and Dutch carriers of p.R59W and it was suggested that this mutation was introduced to South Africa by Dutch settlers at the end of the 17th century. OBJECTIVES: To perform extended haplotype analysis in six South African and Dutch VP families with the p.R59W mutation. METHODS: Haplotyping of 13 microsatellite markers flanking the PPOX gene on chromosome 1q22-23 and five informative single nucleotide polymorphisms within and around the gene. RESULTS: A core haplotype cosegregated in all families studied. CONCLUSIONS: Our data deliver further confirmation that the South African and Dutch VP families carrying mutation p.R59W shared a common ancestor.

A novel mutation in the L12 domain of keratin 1 is associated with mild epidermolytic ichthyosis.

BACKGROUND: Epidermolytic ichthyosis (EI), previously termed bullous congenital ichthyosiform erythroderma or epidermolytic hyperkeratosis, is a clinically heterogeneous genodermatosis caused by mutations in the genes encoding the suprabasal keratins 1 and 10. Classical EI is clinically characterized by severe neonatal erythroderma, blistering and fragile skin in infancy, quickly subsiding with subsequent development of generalized scaling hyperkeratosis. We report three Dutch families with palmoplantar keratoderma and mild blistering, but without neonatal erythroderma and generalized scaling. A novel heterozygous missense mutation in the linker L12 domain of KRT1:c.1019A>G, p.Asp340Gly was found associated with this phenotype in these families. OBJECTIVES: To investigate the effects of the novel KRT1:p.Asp340Gly and the one other previously reported KRT1:p.Asp340Val mutations on keratinocyte cytoskeleton formation and stress resistance. METHODS: Wild-type and mutant pEGFP-KRT1 fusion constructs were transfected into HaCaT cells and exposed to hypo-osmotic shock. Haplotyping and genealogical studies were performed to investigate the possibility of a common founder for p.Asp340Gly. RESULTS: Cells transfected with either one of the keratin 1 L12 domain mutations showed significantly increased tonofilament aggregation. The haplotype around the KRT1 gene was shared in all affected family members of two families and a common founder was traced. CONCLUSIONS: Our study supports the pathogenicity of the keratin 1 L12 domain mutations in vitro. These mutations are associated with a milder EI phenotype with pronounced palmoplantar keratoderma, and without neonatal erythroderma and scaling. The KRT1:p.Asp340Gly mutation in the Dutch families is likely to have arisen from a common founder.

Novel missense mutations in the FOXC2 gene alter transcriptional activity.

Mutations in the FOXC2 gene that codes for a forkhead transcription factor are associated with primary lymphedema that usually develops around puberty. Associated abnormalities include distichiasis and, very frequently, superficial and deep venous insufficiency. Most mutations reported so far either truncate the protein or are missense mutations in the forkhead domain causing a loss of function. The haplo-insufficient state is associated with lymphatic hyperplasia in mice as well as in humans. We analyzed the FOXC2 gene in 288 patients with primary lymphedema and found 11 pathogenic mutations, of which 9 are novel. Of those, 5 were novel missense mutations of which 4 were located outside of the forkhead domain. To examine their pathogenic potential we performed a transactivation assay using a luciferase reporter construct driven by FOXC1 response elements. We found that the mutations outside the forkhead domain cause a gain of function as measured by luciferase activity. Patient characteristics conform to previous reports with the exception of distichiasis, which was found in only 2 patients out of 11. FOXC2 mutations causing lymphedema-distichiasis syndrome reported thus far result in haplo-insufficiency and lead to lymphatic hyperplasia. Our results suggest that gain-of-function mutations may also cause lymphedema. One would expect that in this case, lymphatic hypoplasia would be the underlying abnormality. Patients with activating mutations might present with Meige disease.

Identification of a recurrent mutation in the protoporphyrinogen oxidase gene in Swiss patients with variegate porphyria: clinical and genetic implications.

Variegate porphyria (VP), one of the acute hepatic porphyrias, results from an autosomal dominantly inherited deficiency of protoporphyrinogen oxidase (PPOX), the seventh enzyme in heme biosynthesis. Affected individuals can develop both cutaneous symptoms and potentially life-threatening neurovisceral attacks. Thirty unrelated VP index patients and families are currently known in the Swiss Porphyrin Reference Laboratory in Zürich. In 16 of a total of 24 genetically tested families, we detected a recurrent mutation in the PPOX gene, designated 1082-1083insC, reflecting a prevalence of 67%. Haplotype analysis revealed that 1082-1083insC arose on a common genetic background and, thus, represents a novel founder mutation in the Swiss population. Knowledge on the carrier status within a family does not only allow for adequate genetic counseling but also for prevention of the potentially life-threatening acute porphyric attacks. Hence, future molecular screening in Swiss VP patients might be facilitated by first seeking for mutation 1082-1083insC.

Exclusion of ferrochelatase gene mutations in patients with seasonal palmoplantar keratoderma.

Erythropoietic protoporphyria (EPP) is an autosomal dominant disorder that results from a deficiency of ferrochelatase (FECH), the last enzyme in the heme biosynthetic pathway. The characteristic clinical symptoms usually manifest in early childhood on the sun-exposed areas of the body. They are due to protoporphyrin-induced photosensitivity and include pain, burning and stinging of the skin, followed by erythema and edema. Recently, the occurrence of predominantly seasonal palmar and palmoplantar keratoderma in patients with homozygous mutations in the FECH gene has been reported. These data suggested that palmoplantar keratoderma might be a clinical sign of EPP. Palmoplantar keratodermas (PPKs) are a heterogeneous group of genetic skin diseases and include a seasonal variant, erythrokeratolysis hiemalis et estivalis (EH), also known as keratolytic winter erythema. Because the skin symptoms in the latter disorder are similar to those reported for recessive EPP we examined the FECH gene in three unrelated Dutch Caucasian patients with a previous diagnosis of EH in whom mutations in several other genes had been excluded. However, sequencing analysis of the entire coding regions and the adjacent splice sites of the FECH gene in these individuals revealed absence of mutations. Hence, our data largely exclude the possibility that FECH mutations might be responsible for the palmoplantar skin phenotype observed in EH.

A 2-bp deletion in the GJA1 gene is associated with oculo-dento-digital dysplasia with palmoplantar keratoderma.

Oculo-dento-digital dysplasia (ODDD, OMIM no. 164210) is a pleiotropic disorder characterized mainly by ocular anomalies, varying degrees of finger and toe syndactyly, and enamel defects. It is caused by missense mutations in the gene coding for the gap junction protein connexin 43 or GJA1. Other types of mutations have so far not been reported. Here we describe a Dutch kindred with ODDD showing a new symptom, palmoplantar keratoderma, and associated with a novel 2-bp deletion mutation of GJA1. The dinucleotide deletion 780_781delTG is located in the cytoplasmic C-terminal loop and leads to a frameshift. This is predicted to lead to the production of a slightly truncated protein with 46 incorrect amino acids in the C-terminal cytoplasmic loop (C260fsX307). This novel mutation may explain the presence of skin symptoms.

Computing with DNA by operating on plasmids.

A new method of computing using DNA plasmids is introduced and the potential advantages are listed. The new method is illustrated by reporting a laboratory computation of an instance of the NP-complete algorithmic problem of computing the cardinal number of a maximal independent subset of the vertex set of a graph. A circular DNA plasmid, specifically designed for this method of molecular computing, was constructed. This computational plasmid contains a specially inserted series of DNA sequence segments, each of which is bordered by a characteristic pair of restriction enzyme sites. For the computation reported here, the DNA sequence segments of this series were used to represent the vertices of the graph being investigated. By applying a scheme of enzymatic treatments to the computational plasmids, modified plasmids were generated from which the solution of the computational problem was selected. This new method of computing is applicable to a wide variety of algorithmic problems. Further computations in this style are in progress.