Autosomal dominant spondylocarpotarsal synostosis syndrome: phenotypic homogeneity and genetic heterogeneity

Spondylocarpotarsal synostosis syndrome (SCT) (OMIM 272460), originally thought to be a failure of normal spine segmentation, is characterized by progressive fusion of vertebras and associates unsegmented bars, scoliosis, short stature, carpal and tarsal synostosis. Cleft palate, sensorineural or mixed hearing loss, joint limitation, clinodactyly, and dental enamel hypoplasia are variable manifestations. Twenty-five patients have been reported. Thirteen affected individuals were siblings from six families and four of these families were consanguineous. In four of those families, Krakow et al. [Krakow et al. (2004) Nat Genet 36:405-410] found homozygosity or compound heterozygosity for mutations in the gene encoding FLNB. This confirmed autosomal recessive inheritance of the disorder. We report on two new patients (a mother and her son) representing the first case of autosomal dominant inheritance. These patients met the clinical and radiological criteria for SCT and did not present any features which could exclude this diagnosis. Molecular analysis failed to identify mutations in NOG and FLNB. SCT is therefore, genetically heterogeneous. Both dominant and autosomal recessive forms of inheritance should be considered during genetic counseling.     

Clinical and genetic heterogeneity of Seckel syndrome

Seckel syndrome is a rare autosomal recessive condition belonging to the group of osteodysplastic primordial "dwarfism" and characterized by the association of 1) severe pre- and postnatal growth retardation, 2) microcephaly with mental retardation, and 3) specific dysmorphic features. Recently, two disease loci have been mapped to chromosomes 3q22.1-q24 and 18p11.31-q11.2, respectively, by homozygosity mapping in consanguineous families. Here, we report on the exclusion of these loci in five consanguineous and one multiplex nonconsanguineous Seckel syndrome families and in two consanguineous families presenting type II osteodysplastic primordial dwarfism. These results support the view that Seckel syndrome is a clinically and genetically heterogeneous condition.     

Clinical variability and genetic homogeneity of the camptodactyly-arthropathy-coxa vara-pericarditis syndrome

The camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP) is an autosomal recessive condition characterized by the association of congenital or early onset camptodactyly and noninflammatory arthropathy with synovial hyperplasia. Progressive coxa vara deformity and/or noninflammatory pericardial or pleural effusions have been observed in some patients. Recently, the disease gene has been assigned to human chromosome region 1q25-q31, and truncating mutations have been identified in the megakaryocyte stimulating factor gene. Studying 12 patients from 8 unrelated families, we emphasized hip and spine involvement, particularly in the course of the disease as shown in a 58-year-old patient. Despite clinical variability, linkage studies support genetic homogeneity of the disease.     

Weill-Marchesani syndrome in mother and son

A mother and son, each showing the characteristic features of the Weill-Marchesani syndrome, are described. It is suggested that this family provides further evidence for genetic heterogeneity in this condition.     

Clinical and genetic heterogeneity in Melkersson-Rosenthal Syndrome

Melkersson Rosenthal syndromes (MRS) is a rare autosomal dominantly inherited neurocutaneous syndrome characterised by a triad of facial (seventh cranial) nerve palsy, recurrent orofacial swelling and fissuring of the tongue. A recent report implicated a heterozygous missense variant in SLC27A1 (FATP1) as the cause of this condition in members of an affected Chinese family. We undertook Sanger sequencing of this gene in 14 affected unrelated individuals affected by MRS. We did not detect any putative pathogenic variants. Our data indicates that there is both clinical and genetic heterogeneity in this condition and that the causative gene remains to be identified for the majority of cases.     

Clinical and genetic heterogeneity in Desbuquois dysplasia

Desbuquois dysplasia is a rare chondrodysplasia of autosomal recessive inheritance characterized by short stature, joint laxity, facial anomalies, a "Swedish key" appearance of the proximal femur, and advanced carpal and tarsal bone age. Patients with Desbuquois dysplasia can be divided in two groups, depending on whether hand changes include an extra ossification center distal to the second metacarpal and whether phalangeal dislocations are present or absent. We have recently reported linkage of a Desbuquois dysplasia gene to 17q25.3 in a group of patients with typical hand abnormalities. Here, we report on the exclusion of the 17q25.3 locus in three inbred Desbuquois families originated from Turkey, Asia, and Morocco without typical hand abnormalities. Microsatellite DNA markers from the 17q25.3 region were used at an average spacing of 2 cM, and the three affected individuals from families 1 to 3 were heterozygous for the 17q25.3 region. These results allow us to exclude this region as the locus in Desbuquois families with no hand anomalies and demonstrate genetic heterogeneity. Ongoing studies will hopefully lead to the identification of the responsible genes.     

Clinical and genetic heterogeneity of hypochondroplasia.

Hypochondroplasia (HCH) is an autosomal dominant condition characterised by short stature, micromelia, and lumbar lordosis. In a series of 29 HCH probands (13 sporadic cases, 16 familial cases), we tested their DNA for the N540K recurrent mutation previously described in the proximal tyrosine kinase domain of the FGFR3 gene on chromosome 4p16.3, and we detected this mutation in 21/29 HCH patients. Interestingly, three familial cases were clearly unlinked to chromosome 4p16.3. Reviewing the clinical and radiological manifestations of the disease a posteriori, we observed that the N540K mutation was associated with relative macrocrania with a high and large forehead and short hands. By contrast, in the three pedigrees inconsistent with linkage to chromosome 4p16.3, the clinical phenotype was milder, macrocephaly and shortening of the long bones was less obvious, the hands were normal, and no metaphyseal flaring was noted. This study supports the view that HCH is a clinically and genetically heterogeneous condition.     

Clinical and genetic heterogeneity in keratosis follicularis spinulosa decalvans

Keratosis follicularis spinulosa decalvans (KFSD) is an uncommon genodermatosis mainly characterized by follicular hyperkeratosis, progressive cicatricial alopecia and photophobia. Although an excess of affected males and linkage studies strongly suggest an X-linked pattern of inheritance, an apparently rarer autosomal dominant form with prominent follicular inflammation has also been postulated. We report on a three-generation family with five affected individuals and male-to-male transmission. In addition to widespread keratosis pilaris, cicatricial alopecia and eye involvement, our patients show diffuse facial erythema, recurrent folliculitis, enamel hypoplasia, and thickened nails. A literature review of the last 50 years identified 43 additional KFSD cases. X-linked inheritance is demonstrated in two pedigrees by linkage studies and suspected in five. An autosomal dominant pattern is confirmed in three families, including ours, by male-to-male transmission and considered likely in four. Marked facial erythema, extensive folliculitis, onychodystrophy and multiple caries are frequently reported in the autosomal dominant variant, while palmo-plantar keratoderma and early onset seem more typical of the X-linked form. Moreover, three sporadic male patients showing additional multisystemic abnormalities might be explained by an X-linked contiguous-gene syndrome.     

Clinical and genetic heterogeneity in Mexican patients with ulcerative colitis

Ulcerative colitis (UC) is an inflammatory bowel disease of unknown etiology. Genetic factors implied on its onset and severity may include genes located within the class II major histocompatibility complex (MHC) region. The aim of this study was to determine the relationship between human leukocyte antigen (HLA)-DRB1 alleles with the clinical disease patterns of UC in Mexican Mestizo patients. High-resolution HLA typing was performed by polymerase chain reaction-sequence specific oligonucleotide (PCR)-SSO reverse dot blot and PCR-single-strand polymorphism in 67 patients with UC and 99 ethnically matched healthy controls. UC patients overall showed an increased frequency of HLA-DR1 as compared with healthy controls (17.1% versus 5%, [pC = 0.003, OR = 3.9]). Patients with extensive colitis showed increased frequencies of HLA-DR1 (pC = 1 x 10(-10), OR = 13.9), HLA-DRB1*0103 (pC = 1 x 10(-3), OR = 21.7), HLA-DRB1*0102 (pC = 0.007, OR = undetermined), and HLA-DR15 (pC = 1 x 10(-3), OR = 8.5) when compared with healthy controls. We also found a statistically increased frequency of HLA-DR15 in UC patients with extensive colitis compared with UC patients with only distal colitis (18.7% versus 1.8%, pC = 0.03; OR = 12.2). When patients who underwent proctocolectomy were compared with those who did not, an increased frequency of HLA-DRB1*0103 was observed (21.8% versus 4.9%; pC = 0.03; OR = 5.4; 95% confidence interval, 1.39-21.93). Also, patients with proctocolectomy showed increased frequencies of HLA-DR1 (pC = 1 x 10(-3), OR = 24.2) and HLA-DRB1*0103 (pC = 1 x 10(-3), OR = 50.6) when compared with healthy controls. We concluded that HLA-DR1 is associated with genetic susceptibility to UC in the Mexican Mestizo population. HLA-DR15 distinguishes a subgroup of patients with extensive colitis and the HLA-DRB1*0103 allele distinguishes a subgroup of severe form of disease that might require surgical management.     

Evidence of genetic and phenotypic heterogeneity in the Romano-Ward syndrome.

We report two families with phenotypically different forms of Romano-Ward syndrome. In one family, only five of 18 affected subjects are symptomatic, whereas in the other the proportion is three out of five. The families show distinct ECG morphologies, in addition to QT prolongation. Previous reports have shown genetic linkage either to the HLA locus on chromosome 6 or the Harvey-ras oncogene on chromosome 11. No linkage was found to either locus in the families reported here. The implications of phenotypic and genotypic heterogeneity in Romano-Ward syndrome are discussed in relation to the neurogenic and intrinsic models of pathogenesis.     

Clinical variability and genetic homogeneity of the camptodactyly‐arthropathy‐coxa vara‐pericarditis syndrome

The camptodactyly‐arthropathy‐coxa vara‐pericarditis syndrome (CACP) is an autosomal recessive condition characterized by the association of congenital or early onset camptodactyly and noninflammatory arthropathy with synovial hyperplasia. Progressive coxa vara deformity and/or noninflammatory pericardial or pleural effusions have been observed in some patients. Recently, the disease gene has been assigned to human chromosome region 1q25‐q31, and truncating mutations have been identified in the megakaryocyte stimulating factor gene. Studying 12 patients from 8 unrelated families, we emphasized hip and spine involvement, particularly in the course of the disease as shown in a 58‐year‐old patient. Despite clinical variability, linkage studies support genetic homogeneity of the disease. Am. J. Med. Genet. 95:233–236, 2000.     

Clinical and genetic heterogeneity of amyotrophic lateral sclerosis

Although clinical picture of amyotrophic lateral sclerosis (ALS) is a stereotypical one, resulting from combination of signs secondary to dysfunction of both upper motor neuron (UMN) and lower motor neuron (LMN), clinical heterogeneity is a consistent feature of the disease. Age of onset, relative mix of UMN and LMN signs, duration of the disease and association with other conditions are major factors contributing to variable clinical phenotypes. Genetically, familial forms of ALS are associated with a large number of pleiotropic genes whose mutations impair different biochemical pathways, resulting in overlapping clinical and pathological phenotypes. Over the last few years contribution of large‐ and low‐effect genes to sporadic ALS is increasingly recognized.     

Genetic variation in ICF syndrome: evidence for genetic heterogeneity

ICF syndrome is a rare autosomal recessive immunoglobulin deficiency, sometimes combined with defective cellular immunity. Other features that are frequently observed in ICF syndrome patients include facial dysmorphism, developmental delay, and recurrent infections. The most diagnostic feature of ICF syndrome is the branching of chromosomes 1, 9, and 16 due to pericentromeric instability. Positional candidate cloning recently discovered the de novo DNA methyltransferase 3B (DNMT3B) as the responsible gene by identifying seven different mutations in nine ICF patients. DNMT3B specifically methylates repeat sequences adjacent to the centromeres of chromosome 1, 9, and 16. Our panel of 14 ICF patients was subjected to mutation analysis in the DNMT3B gene. Mutations in DNMT3B were discovered in only nine of our 14 ICF patients. Moreover, two ICF patients from consanguineous families who did not show autozygosity (i.e. homozygosity by descent) for the DNMT3B locus did not reveal DNMT3B mutations, suggesting genetic heterogeneity for this disease. Mutation analysis revealed 11 different mutations, including seven novel ones: eight different missense mutations, two different nonsense mutations, and a splice-site mutation leading to the insertion of three aa's. The missense mutations occurred in or near the catalytic domain of DNMT3B protein, indicating a possible interference with the normal functioning of the enzyme. However, none of the ICF patients was homozygous for a nonsense allele, suggesting that absence of this enzyme is not compatible with life. Compound heterozygosity for a missense and a nonsense mutation did not seem to correlate with a more severe phenotype.     

Pendred syndrome: evidence for genetic homogeneity and further refinement of linkage.

Pendred syndrome is the association between congenital sensorineural deafness and goitre. The disorder is characterised by the incomplete discharge of radioiodide from a primed thyroid following perchlorate challenge. However, the molecular basis of the association between hearing loss and a defect in organification of iodide remains unclear. Pendred syndrome is inherited as an autosomal recessive trait and has recently been mapped to 7q31 coincident with the non-syndromic deafness locus DFNB4. To define the critical linkage interval for Pendred syndrome we have studied five kindreds, each with members affected by Pendred syndrome. All families support linkage to the chromosome 7 region, defined by the microsatellite markers D7S501-D7S523. Detailed haplotype analysis refines the Pendred syndrome linkage interval to a region flanked by the marker loci D7S501 and D7S525, separated by a genetic distance estimated to be 2.5 cM. As potential candidate genes have as yet not been mapped to this interval, these data will contribute to a positional cloning approach for the identification of the Pendred syndrome gene.     

New evidence for genetic heterogeneity of the Freeman-Sheldon syndrome

We report on two sibs (a boy and a girl) with the Freeman-Sheldon (FS) syndrome (also called cranio-carpo-tarsal "dysplasia" or whistling face syndrome), born to normal parents. This unusual finding may represent genetic heterogeneity, germinal mutation of an autosomal dominant gene, and an epistatic recessive gene that suppressed the expression of the abnormal gene in the father, his parents being first cousins. The last 2 mechanisms seem less probable.     

Genetic heterogeneity in Leigh syndrome: Highlighting treatable and novel genetic causes

Leigh syndrome (LS), the most common childhood mitochondrial disorder, has characteristic clinical and neuroradiologic features. Mutations in more than 75 genes have been identified in both the mitochondrial and nuclear genome, implicating a high degree of genetic heterogeneity in LS. To profile these genetic signatures and understand the pathophysiology of LS, we recruited 64 patients from 62 families who were clinically diagnosed with LS at Seoul National University Children's Hospital. Mitochondrial genetic analysis followed by whole-exome sequencing was performed on 61 patients. Pathogenic variants in mitochondrial DNA were identified in 18 families and nuclear DNA mutations in 22. The following 17 genes analyzed in 40 families were found to have genetic complexity: MTATP6, MTND1, MTND3, MTND5, MTND6, MTTK, NDUFS1, NDUFV1, NDUFAF6, SURF1, SLC19A3, ECHS1, PNPT1, IARS2, NARS2, VPS13D, and NAXE. Two treatable cases had biotin-thiamine responsive basal ganglia disease, and another three were identified as having defects in the newly recognized genes (VPS13D or NAXE). Variants in the nuclear genes that encoded mitochondrial aminoacyl tRNA synthetases were present in 27.3% of cases. Our findings expand the genetic and clinical spectrum of LS, showing genetic heterogeneity and highlighting treatable cases and those with novel genetic causes.