Germline Mutations in RASA1 Are Not Found in Patients with Klippel-Trenaunay Syndrome or Capillary Malformation with Limb Overgrowth.

The RASA1 gene encodes p120RASGAP, a multidomain cytoplasmic protein that acts as a negative regulator of the RAS signalling pathway. Heterozygous loss-of-function RASA1 mutations were identified in patients with Parkes Weber syndrome and multifocal capillary malformations. This syndrome is characterised by a capillary blush on an extremity, arteriovenous microfistulas, and bony and soft tissue hypertrophy. The aim of this study was to test RASA1 in 2 disorders characterised by asymmetric limb enlargement and vascular malformations, namely Klippel-Trenaunay syndrome and regional capillary malformation with overgrowth. We did not identify any clear pathogenic change in these patients. Thus, besides clinical and radiological criteria, RASA1 testing constitutes an additional tool to differentiate Parkes Weber syndrome of capillary malformation-arteriovenous malformation (CM-AVM) from overlapping disorders.

Phenotypic variability in 49 cases of ESCO2 mutations, including novel missense and codon deletion in the acetyltransferase domain, correlates with ESCO2 expression and establishes the clinical criteria for Roberts syndrome.

BACKGROUND: Roberts syndrome (RBS) and SC phocomelia are caused by mutations in ESCO2, which codes for an acetyltransferase involved in the regulation of sister chromatid cohesion. Of 26 mutations described to date, only one missense mutation has been reported and all others are predicted to be truncating mutations. Genotype-phenotype analysis has been hampered by limited numbers of patients with clinical information available. OBJECTIVE: To provide unpublished clinical data for 31 patients with proven ESCO2 mutations and combine this series with previously reported clinical and mutation data on 18 cases. Methods Genotype-phenotype correlations and functional effects of two novel ESCO2 mutations were analysed. In situ hybridisation on human embryos at Carnegie stages 14, 17 and 21 was performed to study ESCO2 expression during development. RESULTS AND CONCLUSIONS: Using the cohort of 49 patients, the clinical criteria for RBS were delineated to include: growth retardation; symmetric mesomelic shortening of the limbs in which the upper limbs are more commonly and severely affected than the lower limbs; characteristic facies with microcephaly. The severity of malformations of the facies correlates with the severity of limb reduction. The occurrence of corneal opacities may be associated with specific mutations. Two new mutations, both in the ESCO2 acetyltransferase domain, are described and their acetylation effects in vitro demonstrated. In situ hybridisation on human embryos showed ESCO2 expression in the brain, face, limb, kidney and gonads, which corresponds to the structures affected in RBS.

Clinical, enzymatic, and molecular genetic characterization of a biochemical variant type of argininosuccinic aciduria: prenatal and postnatal diagnosis in five unrelated families.

A biochemical variant of argininosuccinate lyase deficiency, found in five individuals, is introduced. In comparison to classical patients, the variant cases of argininosuccinate lyase deficiency were characterized by residual enzyme activity as measured by the incorporation of [14C]citrulline into proteins. The five patients of different ethnic backgrounds presented with relatively mild clinical symptoms, variable age of onset, marked argininosuccinic aciduria and severe, but not complete, deficiency of argininosuccinate lyase. [14C]Citrulline incorporation into proteins, which is completely blocked in classical argininosuccinic aciduria, was only partially reduced in fibroblasts of these patients. Further investigation showed that previous standard conditions of the assay were not optimal. Higher concentrations of citrulline in the incubation medium strongly stimulated 14C incorporation in normal cells, but not in the patients; as a result, the relative incorporation level in the patients dropped to 6-28% compared to 18-75% of normal in the original procedure. Prenatal diagnosis was successfully performed in three of the families. Affected pregnancies were indicated by (partial) deficiency of [14C]citrulline incorporation in chorionic villi and/or increased levels of argininosuccinate in amniotic fluid. Analysis of the ASL gene in the five patients revealed a considerable allelic heterogeneity. Three novel mutations--R385C (2 patients), V178M and R379C--were detected in homozygous states, whereas one patient was compound heterozygous for the known mutations R193Q and Q286R. In conclusion, there are patients of different ethnic backgrounds who are characterized by residual activity of argininosuccinate lyase and who present with less severe clinical courses. In addition, we present an improved biochemical assay for accurate prenatal and postnatal diagnosis.