Linkage disequilibrium mapping in isolated founder populations: diastrophic dysplasia in Finland.

Linkage disequilibrium mapping in isolated populations provides a powerful tool for fine structure localization of disease genes. Here, Luria and Delbrück's classical methods for analysing bacterial cultures are adapted to the study of human isolated founder populations in order to estimate (i) the recombination fraction between a disease locus and a marker; (ii) the expected degree of allelic homogeneity in a population; and (iii) the mutation rate of marker loci. Using these methods, we report striking linkage disequilibrium for diastrophic dysplasia (DTD) in Finland indicating that the DTD gene should lie within 0.06 centimorgans (or about 60 kilobases) of the CSF1R gene. Predictions about allelic homogeneity in Finland and mutation rates in simple sequence repeats are confirmed by independent observations.

Cartilage-hair hypoplasia gene assigned to chromosome 9 by linkage analysis.

Cartilage-hair hypoplasia (CHH) is an autosomal recessive skeletal dysplasia of unknown pathogenesis leading to short-limbed stature. Associated features include hypoplasia of hair, abnormal cellular immunity, deficient erythrogenesis, increased risk of malignancies, Hirschsprung disease, and Diamond-Blackfan type hypoplastic anaemia. We mapped the CHH gene by linkage analysis with 5 markers to chromosome 9. Multipoint linkage analysis gives a lod score of 9.94 for a location between D9S43 and D9S50. Based on strong linkage disequilibrium the closest marker, D9S50, is likely to be less than 1 cM from the gene. No heterogeneity was observed in 14 Finnish families, nor was there evidence of reduced penetrance. These results provide a starting point for the eventual cloning and characterization of the CHH gene.

A recurrent mutation in the tyrosine kinase domain of fibroblast growth factor receptor 3 causes hypochondroplasia.

Hypochondroplasia (MIM 146000) is an autosomal dominant skeletal dysplasia with skeletal features similar to but milder than those seen in achondroplasia. Within the past year, the achondroplasia locus has been mapped to 4p 16.3 (refs 5-7) and mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have been identified in patients with the disorder. More than 95% of 242 cases reported so far are accounted for by a single Gly380Arg mutation. McKusick et al. proposed that achondroplasia and hypochondroplasia are allelic based on the similarities in phenotype between the two disorders and the identification of a severely dwarfed individual whose father had achondroplasia and whose mother had hypochondroplasia. There is also genetic linkage evidence that hypochondroplasia and achondroplasia map to the same locus. We therefore began a systematic screening of FGFR3 to detect mutations in patients with hypochondroplasia. We now report a single FGFR3 mutation found in 8 out of 14 unrelated patients with hypochondroplasia. This mutation causes a C to A transversion at nucleotide 1620, resulting in an Asn540Lys substitution in the proximal tyrosine kinase domain.

Abnormal copper metabolism and deficient lysyl oxidase activity in a heritable connective tissue disorder.

Biochemical abnormalities were studied in two brothers with bladder divericulas, inguinal hernias, slight skin laxity, and hyperelasticity and skeletal abnormalities including occipital exostoses. Lysyl oxidase activity was low in the medium of cultured skin fibroblasts, this abnormality being accompanied by reduced conversion of the newly synthesized collagen into the soluble form. Copper concentrations were markedly elevated in the cultured skin fibroblasts, but decreased in the serum and hair. Serum cerulophasmin levels were also low. The reduced lysyl oxidase activity is suggested to be responsible for ther clinical manifestations, but the deficiency in this copper-dependent enzyme may be secondary to the abnormalities in the metabolism of the cation. Nevertheless, a mutation directly affecting both lysyl oxidase and an intracellular copper transport protein cannot be excluded. The disease is tentatively classified as one subtype of the Ehlers-Danlos syndrome.

Sensitivity of conformation sensitive gel electrophoresis in detecting mutations in Marfan syndrome and related conditions.

OBJECTIVE: It has been firmly established that mutations in the gene for fibrillin 1, FBN1, cause Marfan syndrome (MFS). FBN1 mutations can also cause other phenotypes, such as ectopia lentis (EL) and familial isolated thoracic aortic aneurysm and dissection (FAA). When the clinical presentation is typical, diagnosis of MFS is usually easy to make. However, there can be a marked phenotypic variation between affected subjects even in one family, and making the diagnosis can be challenging, especially in childhood. The objective of this study was to test the sensitivity of conformation sensitive gel electrophoresis (CSGE) for detecting mutations in FBN1 in MFS and related phenotypes. DESIGN: Setting up CSGE analysis for the FBN1 gene and testing the method first by screening coded samples from 17 MFS patients with previously detected FBN1 mutations. We then used a test set consisting of 46 coded samples representing MFS, related phenotypes, and controls. RESULTS: Sixteen of the 17 known mutations were detected. Altogether 23 mutations were detected in a test set consisting of 46 coded samples representing MFS, related phenotypes, and controls. Nineteen of the mutations were novel. The mutation was detected in 18 of the 20 MFS patients and in one patient with familial EL, but not in a patient with sporadic MASS syndrome, any of the five sporadic annuloaortic ectasia (AAE) patients, or any of the 15 controls. A FBN1 mutation was detected in four members of a multigeneration family with AAE, however. CONCLUSIONS: These results indicate that CSGE is highly sensitive for the detection of mutations in FBN1, and that molecular diagnostics is a useful means of confirming clinical diagnoses of MFS and related disorders. Further careful investigations are needed, however, in order to correlate the interfamilial and intrafamilial clinical variabilities of fibrillinopathies and mutations in FBN1.

Data from subjects receiving intrathecal laronidase for cervical spinal stenosis due to mucopolysaccharidosis type I.

Five subjects with mucopolysaccharidosis type I and symptomatic cervical spinal stenosis received intrathecal laronidase in a 4-month pilot study and/or a 12-month extension study [1]. Clinical descriptions of study subjects, nonserious adverse events, individual data tables, and scoring system methods are provided. There were ten nonserious adverse events that occurred in more than one study subject. Somatosensory evoked potentials were absent in two subjects and normal in two subjects, limiting their utility as an endpoint. There were no significant changes in magnetic resonance imaging of cervical spinal cord or brain, pulmonary function tests, or cerebrospinal fluid opening pressure. These data are presented along with the scoring methods used in evaluation of the study subjects.

Identification of fifteen novel PHEX gene mutations in Finnish patients with hypophosphatemic rickets.

We have carried out a mutation screening of the PHEX gene in Finnish patients with hypophosphatemia. A total of 100% (5/5) of the familial HYP patients (X-linked hypophosphatemia) and 93% (14/15) of the sporadic cases were found to carry a mutation in the PHEX gene. We identified 18 mutations, of which 15 were novel. We report also a new polymorphism 46bp upstream of exon 16. Two families were segregating the same nonsense mutation in exon 1 (R20X), but since this mutation has been previously reported in three independent studies, we consider it to be a mutational hotspot rather than a Finnish founder mutation. We did not find PHEX gene mutations in two additional hypophosphatemia families in which the mode of inheritance was other than X-linked dominant. Also, no mutation could be detected in a patient with suspected oncogenic osteomalacia (OHO).

Anemia in children with cartilage-hair hypoplasia is related to body growth and to the insulin-like growth factor system.

Cartilage-hair hypoplasia (CHH) is a metaphyseal chondrodysplasia characterized by severe short-limbed short stature, hypoplastic hair, and defective immunity. The patients also have anemia. As GH may regulate both body growth and erythropoiesis, we used CHH as a clinical model to study their interrelationships. Retrospective analysis of hematological data of 114 patients showed that the severity of the anemia and macrocytosis in CHH varies with age. The anemia was most severe in early childhood. A prospective study of 21 patients with CHH showed that height correlates with hemoglobin (P = 0.006) and mean corpuscular volume of red blood cells (P < 0.0001). The individual hemoglobin levels correlated with the GH parameters [P = 0.035 for insulin-like growth factor I (IGF-I) and P = 0.002 for IGF-binding protein-3], and the mean corpuscular volume of red blood cell values correlated with fetal hemoglobin. Bone marrow cultures obtained from six patients with CHH showed reduced or totally absent erythroid colony formation, which was not influenced by GH or IGF-I in vitro or by GH treatment in vivo. In patients with CHH, we observed an association between erythropoiesis and growth. We conclude that body growth and erythropoiesis share common regulators. One of these is the GH-IGF-I axis; other factors, as not yet identified, may also be important.

Proteoglycan sulfation in cartilage and cell cultures from patients with sulfate transporter chondrodysplasias: relationship to clinical severity and indications on the role of intracellular sulfate production.

Mutations in the diastrophic dysplasia sulfate transporter (DTDST) gene have been associated with a family of chondrodysplasias that includes diastrophic dysplasia (DTD), atelosteogenesis type 2 (AO2) and the lethal condition achondrogenesis type 1B (ACG1B). There is a correlation between the nature of the mutations and the clinical phenotype, but our understanding of the pathophysiology of the disorder, which involves defective sulfation of cartilage proteoglycans, is far from complete. To evaluate the degree of proteoglycan undersulfation in vivo, we have extracted chondroitin sulfate proteoglycans from cartilage of twelve patients with sulfate transporter chondrodysplasias and analyzed their disaccharide composition by HPLC after digestion with chondroitinase ABC. The amount of non-sulfated disaccharide was elevated in patients' samples (controls, 5.5%+/-2.8 (n=10); patients, 11% to 77%), the highest amount being present in ACG1B patients, indicating that undersulfation of chondroitin sulfate proteoglycans occurs in cartilage in vivo and is correlated with the clinical severity. To investigate further the biochemical mechanisms responsible for the translation of genotype to phenotype, we have studied fibroblast cultures of patients with DTD, AO2 and ACG1B, and controls, by double-labelling with [35S]sulfate and [3H]glucosamine. The incorporation of extracellular sulfate, estimated by the 35S/3H ratio in proteoglycans, was reduced in all patients' cells, with ACG1B cells showing the lowest values. However, disaccharide analysis of chondroitin sulfate proteoglycans showed that these were normally sul fated or only moderately undersulfated; marked undersulfation was observed only after addition of the artificial glycosaminoglycan-chain initiator, beta-D-xyloside, to the culture medium. These results suggest that, while utilization of extracellular sulfate is impaired, fibroblasts can replenish their intracellular sulfate pool by oxidizing sulfur-containing compounds (such as cysteine) and thus partially rescue PG sulfation under basal conditions. This rescue pathway becomes insufficient when GAG synthesis rate is stimulated by beta-D-xyloside. These findings may explain why phenotypic consequences of DTDST mutations are restricted to cartilage, a tissue with high GAG synthesis rate and poor vascular supply, and imply that pharmacological therapy aimed at restoring the intracellular sulfate pool might improve PG sulfation in DTD and related disorders.

Uniparental disomy in cartilage-hair hypoplasia.

Cartilage-hair hypoplasia (CHH) is an autosomal recessive disorder that presents with pleiotropic manifestations including impaired skeletal growth and cellular immunity. It is most prevalent among two founder populations, the Old Order Amish in the USA and the Finns. The gene has been localized to 9p13 by linkage analysis and linkage disequilibrium mapping. A statistically significant deficiency of affected members resulting in a lower than expected segregation ratio has been reported in the Amish, but was not found in a previous study in Finnish CHH families. Reduced penetrance was the mechanism suggested in the Amish, but could not be verified by haplotype analyses performed after the assignment of the CHH gene. Here we have carried out segregation analysis of 101 Finnish CHH families, but again, evidence of a significant deficiency of affected members was not found. Nevertheless, among 54 uniplex families, 2 patients with CHH and uniparental disomy (UPD) for chromosome 9 were discovered. UPD might contribute to low segregation ratios by increasing the number of families with only 1 affected individual. These observations show that UPD may occur in an unexpectedly high number of the patients and should be taken into account in the genetic counselling and prenatal diagnostics of CHH families.

Identification of the Finnish founder mutation for diastrophic dysplasia (DTD).

Diastrophic dysplasia (DTD) is especially prevalent in Finland and the existence of a founder mutation has been previously inferred from the fact that 95% of Finnish DTD chromosomes have a rare ancestral haplotype found in only 4% of Finnish control chromosomes. Here we report the identification of the Finnish founder mutation as a GT-> GC transition (c.-26 + 2T > C) in the splice donor site of a previously undescribed 5'-untranslated exon of the diastrophic dysplasia sulfate transporter gene (DTDST); the mutation acts by severely reducing mRNA levels. Among 84 DTD families in Finland, patients carried two copies of the mutation in 69 families, one copy in 14 families, and no copies in one family. Roughly 90% of Finnish DTD chromosomes thus carry the splice-site mutation, which we have designated DTDST(Fin). Unexpectedly, we found that nine of the DTD chromosomes having the apparently ancestral haplotype did not carry DTDST(Fin), but rather two other mutations. Eight such chromosomes had an R279W mutation and one had a V340del deletion. We consider the possible implications of presence of multiple DTD mutations on this rare haplotype.

The gene defective in anhidrotic ectodermal dysplasia is expressed in the developing epithelium, neuroectoderm, thymus, and bone.

Anhidrotic ectodermal dysplasia (EDA) is characterized by defects in the development of teeth, hair, and sweat glands. To study the expression of the human gene defective in EDA in human fetal development (Weeks 6-23 of gestational age) and in adult tissues, in situ hybridization and immunohistochemistry were used. First signs of expression were detected at Week 8 in epidermis and in neuroectodermal cells. Starting at Week 12, osteoblasts and thymus were positive for EDA mRNA. Hair follicles expressed EDA mRNA from 18 weeks. The presence of the EDA protein coincided with mRNA expression in the tissues examined. The expression pattern of the EDA gene is consistent with typical involvement of the skin in the syndrome. However, the expression is not limited to the ectodermal tissues and many sites of expression are not obviously reflected in the clinical features of the syndrome.

Apparently new syndrome of short stature, lumbar malsegmentation, and minor facial anomalies in two brothers.

We describe a previously unrecognized syndrome in two brothers with short stature, webbed neck, unusual face, moderate malsegmentation of the lumbar spine, and unilateral Legg-Perthes-Calvé type "disease" of the hip. Autosomal recessive inheritance is proposed, although we cannot exclude the possibility of an X-linked recessive or an autosomal dominant condition with germinal mosaicism.

Craniofacial structure in diastrophic dysplasia--a cephalometric study.

Diastrophic dysplasia (DTD) is a well characterized, recessively inherited osteochondrodysplasia. Forty-eight patients with DTD were studied for craniofacial characteristics. Of these patients, 58% had cleft palate. A cephalometric analysis based on lateral cephalograms was performed. We observed a short anterior cranial base, vertical nasal bones, short and posteriorly positioned upper and lower jaws, increased anterior facial height, increase in the sagittal length of the body of the cervical vertebrae, and an abnormal dens of the second cervical vertebra. DTDST, in which mutations responsible for the disease occur, is a gene that codes for a sulphate transporter membrane protein. The craniofacial anomalies in DTD most likely result from deficient development and growth of cartilaginous structures and are probably due to defective sulfation of the proteoglycans of the cartilage.

Autoimmune enteropathy in Schimke immunoosseous dysplasia.

The clinical phenotype of Schimke immunoosseous dysplasia (SID) is characterized by growth retardation, renal failure, recurrent infections, cerebral infarcts, and skin pigmentation beginning in childhood. We report here on a 4-year-old male child who had all characteristic symptoms of SID, and, in addition, vomiting and prolonged diarrhea. The study results suggest that malabsorption, demonstrated as increased serum immunoglobulin A anti-gliadin antibody, steatorrhea and partial villous atrophy of the jejunal small bowel, is a previously unrecognized feature of SID.

A new form of metaphyseal chondrodysplasia in two sibs: surgical treatment of tracheobronchial malacia and scoliosis.

We describe a 19-year-old male with a previously unrecognized form of disproportionate short stature, tracheobronchial malacia, and progressive scoliosis and his 28-year-old sister with the same but milder condition. The clinical characteristics were short limbs and digits and thoracolumbar scoliosis. Bone films showed progression from marked metaphyseal dysplasia of tubular bones in childhood to short and broad bones with mild dysplasia of the joints in adulthood. The vertebrae and the intervertebral plates were only mildly affected in spite of marked scoliosis. Trachea and bronchi were reinforced with surrounding acrylate mesh before surgical treatment of the scoliosis. Affected sibs of both sexes and healthy parents suggest an autosomal recessive mode of inheritance.

Phenotypic expressions of a Gly 154Arg mutation in type II collagen in two unrelated patients with spondyloepimetaphyseal dysplasia (SEMD).

Type II collagenopathies consist of chondrodysplasias ranging from lethal to mild in severity. A large number of mutations has been found in the COL2A1 gene. Glycine substitutions have been the most common types of mutation. Genotype-phenotype correlations in type II collagenopathies have not been established, partly because of insufficient clinical and radiographic description of the patients. We found a glycine-to-arginine substitution at position 154 in type II collagen in two unrelated isolated propositi with spondyloepimetaphyseal dysplasia and provide a comparative clinical and radiographic analysis from birth to young adulthood for this condition. The clinical phenotype was disproportionate short stature with varus/valgus deformities of the lower limbs requiring corrective osteotomies, and lumbar lordosis. The skeletal radiographs showed an evolution from short tubular bones, delayed epiphyseal development, and mild vertebral involvement to severe metaphyseal dysplasia with dappling irregularities, and hip "dysplasia." The metaphyseal abnormalities disappeared by adulthood.

The spine in diastrophic dysplasia.

Diastrophic dysplasia is an autosomal recessive disorder of the skeleton, characterized by disproportionate short stature, generalized joint deformities, club feet, deformed ear pinnae, and, frequently, spinal deformity and cleft palate. Diastrophic dysplasia is more common in Finland than elsewhere. We studied 101 patients with an age range from newborns to 79 years to find out the frequency and type of spinal deformities, the early signs of progressive cases, and to follow the natural history of the disease. In the follow-up study, 17 patients were under 10 years, 21 under 21 years, and 63 over 21 years of age. One-third of the patients had cervical kyphosis; in the most severe case the kyphosis was 180 degrees and led to quadriplegia during anesthesia. In three patients, cervical kyphosis resolved spontaneously before the age of 5 years. The overall frequency of scoliosis was 37%; 49% in women and 22% in men. Only 13 patients had curves greater than 50 degrees; these curves constituted distinct rotation at the apex from the early evolution of the curve. The early signs of severe curves were detectable at the age of 2 to 4 years. Only two patients were operated on because of scoliosis; one with fusion in situ and the other instrumented with the pediatric Cotrel-Dubousset instrumentation. Three patients had a brace, which did not prevent the progression of the curve. Symptoms referring to a narrow spinal canal were registered in four patients, two of which were operated on; a lumbar posterior decompressive procedure was made at adult age.

Cervical kyphosis in diastrophic dysplasia.

STUDY DESIGN: An evaluation of cervical kyphosis in diastrophic dysplasia from newborn to adult life. OBJECTIVES: To discover the prevalence and natural history of cervical kyphosis in diastrophic dysplasia. SUMMARY OF BACKGROUND DATA: Typical findings in this rare skeletal dysplasia are sport-limbed short stature, multiple joint contractures, early degeneration of joints, and spinal deformities such as cervical kyphosis, scoliosis, and exaggerated lumbar lordosis. In diastrophic dysplasia, spontaneous resolution of cervical kyphosis has been reported, but so have severe forms causing medullar compression leading to quadriplegia and death. The prevalence and clinical outcome of the kyphosis are not known. METHODS: The radiographic natural history of the cervical spine was studied in 120 patients. They varied in age from newborns to 63-year-olds. The average follow-up time in 26 living patients with cervical kyphosis was 10.0 years. RESULTS: Midcervical kyphosis was noted in 29 patients (24%) in their first radiograph. In 25 patients, the first radiographs were taken before the age of 18 months, and 24 of these patients (96%) had cervical kyphosis. The most severe case was that of a 32-year-old patient with a 165 degrees kyphosis. In the 24 patients, the kyphosis resolved spontaneously at an average age of 7.1 years. Three patients with a severe kyphosis died; one patient is alive. One patient, a 4-year-old child has mild resolving deformity. CONCLUSIONS: Cervical kyphosis in diastrophic dysplasia usually is shown at the time of birth. It resolves spontaneously during growth and seldom needs treatment. Careful follow-up study and treatment, if necessary, are important tools for avoiding the neurologic problems and fatal outcome.

Foot deformities in diastrophic dysplasia. An analysis of 102 patients.

The exceptionally high prevalence of diastrophic dysplasia in Finland has enabled us to analyse the foot deformities of 102 patients at their first orthopaedic evaluation and classify 204 feet into five categories. The most common finding (43%) was a foot with tarsal valgus deformity and metatarsus adductus; 37% showed either equinovarus adductus (29%) or equinus (8%) deformities. At the first examination 13% showed metatarsus adductus deformity alone, and 7% were clinically normal. The expression 'club foot', generally used for the foot deformity in diastrophic dysplasia is a misnomer. There is a wide spectrum of deformities, some of them specific for the condition.