Mutations in EXTL3 Cause Neuro-immuno-skeletal Dysplasia Syndrome.

EXTL3 regulates the biosynthesis of heparan sulfate (HS), important for both skeletal development and hematopoiesis, through the formation of HS proteoglycans (HSPGs). By whole-exome sequencing, we identified homozygous missense mutations c.1382C>T, c.1537C>T, c.1970A>G, and c.2008T>G in EXTL3 in nine affected individuals from five unrelated families. Notably, we found the identical homozygous missense mutation c.1382C>T (p.Pro461Leu) in four affected individuals from two unrelated families. Affected individuals presented with variable skeletal abnormalities and neurodevelopmental defects. Severe combined immunodeficiency (SCID) with a complete absence of T cells was observed in three families. EXTL3 was most abundant in hematopoietic stem cells and early progenitor T cells, which is in line with a SCID phenotype at the level of early T cell development in the thymus. To provide further support for the hypothesis that mutations in EXTL3 cause a neuro-immuno-skeletal dysplasia syndrome, and to gain insight into the pathogenesis of the disorder, we analyzed the localization of EXTL3 in fibroblasts derived from affected individuals and determined glycosaminoglycan concentrations in these cells as well as in urine and blood. We observed abnormal glycosaminoglycan concentrations and increased concentrations of the non-sulfated chondroitin disaccharide D0a0 and the disaccharide D0a4 in serum and urine of all analyzed affected individuals. In summary, we show that biallelic mutations in EXTL3 disturb glycosaminoglycan synthesis and thus lead to a recognizable syndrome characterized by variable expression of skeletal, neurological, and immunological abnormalities.

Plasma and urinary glycosaminoglycans in the course of juvenile idiopathic arthritis.

OBJECTIVES: The aim of the study was to perform analyses of plasma and urinary glycosaminoglycan isolated from juvenile idiopathic arthritis (JIA). METHODS, RESULTS: Chondroitin/dermatan sulfate (CS/DS), heparan sulfate/heparin (HS/H) and hyaluronic acid (HA) were evaluated in samples obtained from JIA patients before and after treatment. Electrophoretic analysis of GAGs identified the presence of CS, DS and HS/H in plasma of healthy subjects and JIA patients. CS were the predominant plasma GAGs constituent in all investigated subject. The plasma CS level in untreated patients was significantly decreased. Therapy resulted in an increase in this glycan level. However, plasma CS concentration still remained higher than in controls. Increased levels of DS and HA in untreated JIA patients were recorded. Anti-inflammatory treatment led to normalization of these parameters concentrations. Plasma and urinary concentrations of HS/H were similar in all groups of individuals. Urinary CS/DS and HA were decreased only in untreated patients. CONCLUSIONS: The data presented indicate that changes in plasma and urinary glycosaminoglycan occur in the course of JIA. There are probably the expression of both local articular cartilage matrix and systemic changes in connective tissue remodeling.

Urinary glycosaminoglycan (uGAG) excretion in healthy pediatric and adolescent population.

OBJECTIVES: The influence of age and gender factor on the urinary excretion of total glycosaminoglycans (uGAGs) and their particular types: chondroitin/dermatan sulfates (CS/DSs), heparan sulfates (HSs) and hyaluronan (HA) was analyzed in healthy pediatric and adolescent population. DESIGN AND METHODS: Urine samples were collected from 95 healthy children. Sulfated GAGs excreted in the urine were quantitated using standardized dye-binding method, while the concentrations of HA were determined by immunoassay. RESULTS: Age-dependent decline in total uGAG excretion (r=-0.686; p<0.001), resulting from a decrease in particular GAG fractions i.e. CS/DS (r=-0.757; p<0.001), HS (r=-0.401; p<0.05) and HA (r=-0.638; p<0.001), was found in healthy subjects. The observed differences were not gender specific with the exception of HS, in which excretion declines with age in males (r=-0.501; p<0.05) and does not change in females. Changes in the distribution pattern of uGAG were also found. CS/DS were the predominant uGAG's fraction, representing from 55% to 76% of the total GAGs. Children up to 3 years excreted more GAGs than older subjects and with a higher proportion of CS/DS and less content of HS. Moreover, the relative contribution of HA was increased twofold in adolescents, aged 15-18, as compared to younger subjects. A negative correlation existed between uGAG excretion and body height, except for HS, for which this relationship was found only in males. CONCLUSIONS: Changes in urinary distribution pattern of particular GAG types during physiological human growth and development were found. Evaluation of urinary GAG screening procedures during pathological conditions should be based on the GAG/creatinine ratios with age and gender taken into account.

Polydispersity of glycosaminoglycans in normal human urine.

To elucidate precise nature of urinary glycosaminoglycans (GAG) GAG in the acidic subfractions obtained in a previous paper (Endo et al. 1980) were quantitated by digestion with mucopolysaccharidases, nitrous acid treatment and by quantitative cellulose acetate membrane (Separax) electrophoresis. Hyaluronic acid, chondroitin sulfates and chondroitin, dermatan sulfate and dermatan, heparan sulfate, keratan sulfate, and acidic glycopeptide were found in wide distribution in these subfractions. The results suggested the presence of various degree of the depolymerization products of each GAG and of wide range of the desulfation products of each sulfated GAG. Distribution map of each GAG in the subfractions showed more detailed polydispersity of GAG in normal human urine than that reported previously.

Chemical definition of the mucopolysaccharidoses.

Glycosaminoglycans were isolated from the urines of 46 patients with mucopolysaccharidosis; 11 with Type I (Hurler), 8 with Type II (Hunter), 16 with Type III (Sanfilippo A and B), 9 with Type V (Scheie), one with Type VI (Marateaux-Lamy), and one unclassified. All 46 patients excreted in their urine excessive amounts of dermatan sulfate, heparan sulfate or both. In addition, patients of certain types excreted excessive amounts of chondroitin sulfates A and/or C. There is a trend in each type of the disease towards the same carbazole/orcinol ratio, glucosamine/galactosamine ratio and glycosaminoglycan composition. Molecular weight distribution of the urinary glycosaminoglycans by gel filtration from Sephadex G-200 is characteristic for each different type of mucopolysaccharidosis and is distinguished from normal controls and patients without mucopolysaccharidosis. Preparation of elution diagrams from Sephadex G-200 allows an estimation of the composition of the glycosamino-glycans. Practically all heparan sulfate and a sizable part of dermatan sulfate from the urinary glycosaminoglycans of all these patients have been highly degraded. In all the patients in which the specific enzyme defect was demonstrated, the assignment of the type of mucopolysaccharidosis, on the basis of the elution diagrams, was correct. Patients with mucopolysaccharidosis Type V displayed two conspicuously different types of elution patterns, suggesting heterogeneity. Indeed, only a portion of these patients showed alpha-L- iduronidase deficiency. Carriers had normal urinary glycosaminoglycan output and composition and exhibited normal elution diagrams.