A man, a syndrome, a gene: Clouston's hidrotic ectodermal dysplasia (HED)

This paper presents a biographical sketch of Dr. H. R. Clouston, whose eponym is attached to a type of hidrotic ectodermal dystrophy, and a brief account of the mapping of the gene and its identification as the connexin gene, GJB6.     

有汗型外胚层发育不良一家系的Cx30基因突变检测及产前诊断

目的对一个中国汉族有汗型外胚层发育不良（hidrotic ectodermal dysplasis，HED）家系进行了突变筛查，并在此基础上对该家系中已孕5个月的胎儿进行了产前诊断。方法共收集了该家系2例患者及4名正常人的外周血标本，抽取了胎儿的脐血标本。扩增Cx30基因的整个编码区序列，直接双向测序，突变进一步经内切酶酶切分析验证，在成功地获得基因诊断结果后，进一步进行产前诊断。首先从脐血DNA标本中扩出Cx30基因的整个编码区序列，经内切酶酶切分析检测突变，并进一步将整个编码区序列克隆入T载体，测序验证突变。结果在两个受累患者中检测了相同的突变，即在Cx30基因存在一个263C→T的点突变，该突变导致了在GJB6蛋白第2个跨膜区中氨基酸残基改变（A88V）。胎儿的检测结果表明其基因组中同样存在该致病突变，因此是1个受累胎儿。结论实验数据表明Cx30基因中错义突变A88V也是中国汉族人群中有汗型外胚层发育不良的致病原因之一，可以通过基因诊断和产前诊断阻止致病基因的传递。     

Genome-wide patterns of identity-by-descent sharing in the French Canadian founder population

In genetics the ability to accurately describe the familial relationships among a group of individuals can be very useful. Recent statistical tools succeeded in assessing the degree of relatedness up to 6–7 generations with good power using dense genome-wide single-nucleotide polymorphism data to estimate the extent of identity-by-descent (IBD) sharing. It is therefore important to describe genome-wide patterns of IBD sharing for more remote and complex relatedness between individuals, such as that observed in a founder population like Quebec, Canada. Taking advantage of the extended genealogical records of the French Canadian founder population, we first compared different tools to identify regions of IBD in order to best describe genome-wide IBD sharing and its correlation with genealogical characteristics. Results showed that the extent of IBD sharing identified with FastIBD correlates best with relatedness measured using genealogical data. Total length of IBD sharing explained 85% of the genealogical kinship''s variance. In addition, we observed significantly higher sharing in pairs of individuals with at least one inbred ancestor compared with those without any. Furthermore, patterns of IBD sharing and average sharing were different across regional populations, consistent with the settlement history of Quebec. Our results suggest that, as expected, the complex relatedness present in founder populations is reflected in patterns of IBD sharing. Using these patterns, it is thus possible to gain insight on the types of distant relationships in a sample from a founder population like Quebec.     

Mucolipidosis II: a single causal mutation in the N-acetylglucosamine-1-phosphotransferase gene (GNPTAB) in a French Canadian founder population

Mucolipidosis (ML) II (I-cell disease) is a lysosomal storage disorder caused by a deficiency of UDP- N- acetylglucosamine:lysosomal enzyme N- acetylglucosamine-1-phosphotransferase. MLII is an autosomal recessive disease with a carrier rate estimated at 1/39 in Saguenay–Lac-Saint-Jean (SLSJ) (Quebec, Canada), which is the highest frequency documented worldwide. To identify the causing mutation, we sequenced GNPTAB exons in 27 parents of 16 MLII-deceased children from the SLSJ region as obligatory and potential carriers. We also performed a genealogical reconstruction for each parent to evaluate consanguinity levels and genetic contribution of ancestors. Our goal was to identify which parameters could explain the high MLII frequency observed in the SLSJ population. A single mutation (c.3503_3504delTC) was found in all obligatory carriers. In addition, 11 apparent polymorphisms were identified. The mutation was not detected in genomic DNA of 50 unrelated controls. Genealogical data show six founders (three couples) with a higher probability of having introduced the mutation in the population. The frequency of the mutation was increased as a consequence of this founder effect and of the resulting population structure. We suggest that c.3503_3504delTC is the allele causing MLII in the SLSJ population, and its high carrier rate is most likely explained by a founder effect.     

A founder mutation in the PEX6 gene is responsible for increased incidence of Zellweger syndrome in a French Canadian population

ABSTRACT: BACKGROUND: Zellweger syndrome (ZS) is a peroxisome biogenesis disorder due to mutations in any one of 13 PEX genes. Increased incidence of ZS has been suspected in French-Canadians of the Saguenay-Lac-St-Jean region (SLSJ) of Quebec, but this remains unsolved. METHODS: We identified 5 ZS patients from SLSJ diagnosed by peroxisome dysfunction between 1990--2010 and sequenced all coding exons of known PEX genes in one patient using Next Generation Sequencing (NGS) for diagnostic confirmation. RESULTS: A homozygous mutation (c.802_815del, p.[Val207_Gln294del, Val76_Gln294del]) in PEX6 was identified and then shown in 4 other patients. Parental heterozygosity was confirmed in all. Incidence of ZS was estimated to 1 in 12,191 live births, with a carrier frequency of 1 in 55. In addition, we present data suggesting that this mutation abolishes a SF2/ASF splice enhancer binding site, resulting in the use of two alternative cryptic donor splice sites and predicted to encode an internally deleted in-frame protein. CONCLUSION: We report increased incidence of ZS in French-Canadians of SLSJ caused by a PEX6 founder mutation. To our knowledge, this is the highest reported incidence of ZS worldwide. These findings have implications for carrier screening and support the utility of NGS for molecular confirmation of peroxisomal disorders.     

X-linked hypohidrotic ectodermal dysplasia and t(X;12) in a female

A female patient with features of hypohidrotic ectodermal dysplasia (HED) was found to be a carrier of a de novo t(X;12) with a breakpoint in Xq13.1. This is the second instance of an X/autosome translocation, with apparently the same X breakpoint, reported in HED.     

Ectrodactyly, ectodermal dysplasia and cleft palate (EEC syndrome):Report of a family and review of the literature

A family is described in which a father and son are affected with ectrodactyly, ectodermal dysplasia and cleft palate. This particular constellation of major malformations may constitute a variant form of the EEC syndrome which characteristically includes cleft lip with or without cleft palate. From a review of the cases previously reported in the literature, autosomal dominant inheritance is the most likely mode of transmission of these conditions.     

Genetic homogeneity of the urofacial (Ochoa) syndrome confirmed in a new French family

The urofacial syndrome (UFS) or Ochoa syndrome has been reported as a rare autosomal recessive disorder comprising a uropathy and facial abnormalities. The gene was mapped on chromosome region 10q23-q24. We report the first European cases of UFS. Haplotype analyses in our French family were compared with those previously described in patients from Columbia and America (literature data). The results are compatible with the same localization of the critical region and favor the hypothesis of genetic homogeneity.     

Linkage disequilibrium analysis of childhood-onset spinal muscular atrophy (SMA) in the French -- Canadian population

Spinal muscular atrophy (SMA) is, after Duchenne muscular dystrophy,the most common neuromuscular disorder in childhood. The generesponsible for childhood SMA has been mapped to the q11. 2– q13. 3 region of chromosome 5. We have extended ourlinkage studies of SMA In the French - Canadian population toInclude microsatellite markers at the D5S125, D5S351, D5S435,JK53CA1/ 2 and MAPI B locl. These markers span about 4 cM ofthe SMA candidate region. We observed significant evidence forlinkage between SMA and all the markers tested. The analysisof recombinant chromosomes provide evidence for the followinggenetic order: D5S125-D5S435-MAP1B-3'-JK53CA1/2 and places D5S351proximal to JK53CA1/2. Furthermore, we confirm the current localizationof the SMA gene distal to D5S435. Finally, we provide demonstrationof significant linkage disequilibrium between childhood-onsetSMA and four of the five marker loci, D5S125, D5S435, D5S351and JK53CA1/2. Analysis of SMA-region haplotypes suggests thatthere may be a predominant SMA allele that is present on about17% of SMA chromosomes in this sample of the French - Canadianpopulation. We conclude that the observed linkage disequilibriumis likely due to genetic drift among regions of Quebec, consistentwith this population's early history.     

Genitourinary anomalies are a component manifestation in the ectodermal dysplasia, ectrodactyly, cleft lip/palate (EEC) syndrome

Here we report on 13 individuals with the EEC syndrome from a single craniofacial clinic population. Eight of 13 underwent genitourinary (GU) evaluation; all had abnormal findings. Seven had anomalies of the urinary tract, and 3 had genital anomalies. To our knowledge, this is the first report of GU evaluation of the majority of EEC patients from a single clinic population. Results support the suggestion that GU anomalies are a major component of the EEC syndrome. Genitourinary evaluation of all EEC patients and their first degree relatives seems indicated. The abnormal findings observed to date suggest variable expression of an autosomal dominant gene.     

Fine mapping the candidate region for peripheral neuropathy with or without agenesis of the corpus callosum in the French Canadian population

Peripheral neuropathy with or without agenesis of the corpus callosum (ACCPN [MIM 2180000]) is an autosomal recessive disease characterised by progressive sensorimotor neuropathy, mental retardation, dysmorphic features and complete or partial agenesis of the corpus callosum. The ACCPN gene was mapped in 1996 to a 4 cM region on chromosome 15. We have since collected additional French Canadian (FC) families and typed a total of 11 polymorphic markers spanning approximately 18 cM on chromosome 15. Through the use of haplotype analysis we have confirmed the presence of a founder haplotype in the FC population, and identified critical recombinants which reduce the ACCPN candidate interval to a approximately 2 cM or 1000 Kb region flanked by markers D15S1040 and ACTC. Linkage disequilibrium analysis supports the haplotype data, and suggests that the ACCPN gene lies nearest to marker D15S1232.     

Ectrodactyly (split-hand/split-foot) and ectodermal dysplasia with normal lip and palate in a four-generation kindred

Five members of a four-generation Mauritian family with ectrodactyly (split-hand/split-foot deformity) and ectodermal dysplasia but without clefting of the lip or palate have been investigated. The ectrodactyly ranged from virtual normality to severe tetramelic deficiencies. The ectodermal dysplasia manifested as hypotrichosis and abnormal dentition. Distinction is drawn between this autosomal dominant condition and the classical EEC syndrome; independent syndromic status is proposed.     

Association of ectodermal dysplasia, ectrodactyly, and macular dystrophy: the EEM syndrome.

We report five patients with ectodermal dysplasia, ectrodactyly associated with syndactyly or cleft hand or both, and, in addition, macular dystrophy which was presumed to be progressive, in an isolated population on a remote island in Japan. The heredity of this syndrome was thought to be autosomal recessive. Three cases have been reported so far with a combination of the same abnormalities. The parents in these cases were consanguineous.     

The distribution of HLA alleles revealed a founder effect in the geographically isolated Chinese population, Drung

The Drung ethnic minority is one of the smallest ethnic groups of China, geographically isolated by mountains and rivers. Before 1949, Drung society maintained many vestiges of the primitive commune system. The origin and migration of the Drung and their genetic background are still unknown because of limited records about this population. Here, we for the first time demonstrated the unique distribution of HLA alleles in the Drung by high-resolution sequence-based typing (SBT) method. Number of alleles detected is obviously less than expected and only a few alleles with a high homozygosity in each locus are predominant in this minority. The characteristics of HLA allele distribution in the Drung could reflect founder effects, suggesting the Drung probably descended from very few ancestors. The statistical analysis based on allele frequencies indicated that the Drung was an isolated ethnic group, but it also provided the clue that the Drung was genetically related to Chinese southwestern ethnic groups. Significant reduced allelic diversity and genetic isolate in the Drung make it an ideal homogeneous population and very useful model to study the evolution of HLA and the origin and migration of Chinese ethnic groups. The research paved a way to elucidate the genetic background of this mysterious minority and disease predisposition.     

Mitochondrial DNA polymorphism detected with the restriction enzymes BstNI and BclI in a French Canadian population

The enzymes Bst NI and Bell were used to detect various human mitochondrial DNA RFLPs in a sample of 104 unrelated French Canadians. These sequence variations were found in total white blood cell DNA probed with whole human mitochondrial DNA. With Bst NI, 6 mitochondrial DNA restriction patterns (morphs) were identified. Bst NI morphs 2–6 each differ from morph 1 by one single distinct restriction site gain or loss on the mitochondrial DNA molecule. Although Bst NI morph 1 was found in most of the subjects (80%), each other morph was observed at a frequency of at least 3%. With the enzyme BclI , 4 different morphs were detected. Morphs 2–4 also result from different single restriction site alteration as compared with Bcl I morph 1. The morph 1 was clearly the most frequent (95%) while morphs 3 and 4 were present in only 1% of the subjects. These data indicate that the enzyme Bst NI and, to a much lesser extent, the enzyme Bcl I detect mitochondrial Dn'A polymorphism in Caucasians. They are therefore of interest for population genetics studies.     

Cataracts, alopecia, and sclerodactyly: a previously apparently undescribed ectodermal dysplasia syndrome on the island of Rodrigues

An unique autosomal recessive ectodermal dysplasia is present in 5 sibs from the Indian Ocean island of Rodrigues. The main manifestations are total congenital alopecia, bilateral congenital cataracts, and skin changes of the hands and feet including sclerodactyly, hyperkeratosis, contractures, and pseudoainhum formation. The phenotype differs from that of other genetic ectodermal dysplasias and independent syndromic status is probable.