6q16.3q23.3 duplication associated with Prader-Willi-like syndrome.

BACKGROUND: Prader-Willi syndrome (PWS) is characterized by hypotonia, delayed neuropsychomotor development, overeating, obesity and mental deficiency. This phenotype is encountered in other conditions, defining Prader-Willi-like syndrome (PWLS). CASE PRESENTATION: We report a 14-year-old boy with a complex small supernumerary marker chromosome (sSMC) associated with PWLS. The propositus presents clinical features commonly found in patients with PWLS, including growth hormone deficit. Banding karyotype analysis and fluorescence in situ hybridization (FISH) revealed a marker derived from chromosome 6 and a neocentromere as suspected, but array-CGH enabled us to characterize this marker as a der(10)t(6;10)(6qter → 6q23.3::10p11.1 → 10p11.21)dn. As far as we know, this is the first diagnosed case of PWLS associated with a complex sSMC, involving a 30.9 Mb gain in the 6q16.3q23.3 region and a 3.5 Mb gain in the 10p11.21p11.1 region. Several genes have been mapped to the 6q region including the TCBA1 gene, which is associated with developmental delay and recurrent infections, the ENPP1 gene, associated with insulin resistance and susceptibility to obesity and the BMIQ3 gene, associated with body mass index (BMI). No OMIM gene was found in the smallest 10p11.21p11.1 region. CONCLUSIONS: We suggest that the duplicated chromosome segment 6q16.3q23.3 may be responsible for the phenotype of our case and may also be a candidate locus of PWLS.

Pure direct duplication (12)(q24.1-->q24.2) in a child with Marcus Gunn phenomenon and multiple congenital anomalies.

Partial trisomy of the region 12q24.1-->q24.2 is rare and usually associated with other rearrangements. We report on the clinical and cytogenetic findings in a girl with a pure de novo direct duplication dup(12)(q24.1-->q24.2). She had developmental and growth retardation, facial dysmorphism with upslanting palpebral fissures, wide downturned mouth, short neck, and Marcus Gunn phenomenon. She also had single transverse creases, hypoplasia of the corpus callosum, and cardiac malformations consisting of a bicuspid aortic valve, multiple ventricular septal defects, and kinking of the aorta. The size of the duplication was characterized by molecular cytogenetics and comparative genomic hybridization (CGH) to be 11.5 Mb in size and extended from the BAC probe RP11-256L11 loci (108.2 Mb) +/- 1 Mb to the BAC probe RP11-665J20 loci (119.7 Mb) +/- 1 Mb. No such pure 12q24 duplication was detected out of the 23 patients reported in the literature with duplications in 12q region. Comparison with these reported 12q trisomies suggests the duplication dup(12)(q24.1-->q24.2) is associated with a recognizable phenotype consisting of characteristic facial dysmorphism, growth retardation, and cardiac malformation.

Intrachromosomal insertion mimicking a pericentric inversion: molecular cytogenetic characterization of a three break rearrangement of chromosome 20.

Intrachromosomal insertions are uncommon rearrangements, in which a chromosomal segment is intercalated into another part of the same chromosome. The insertion may occur in the same arm (paracentric) or in the other arm (pericentric). The cytogenetic recognition of these structurally rearranged chromosomes can be difficult, and intrachromosomal insertions can be easily mistaken for inversions. We describe a case of a familial pericentric insertion of chromosome 20, initially misdiagnosed as a pericentric inversion in the healthy carrier and then reinterpreted as insertion in an abnormal child with a recombinant chromosome. Fluorescence in situ hybridization (FISH) allowed us to confirm the mechanism of recombinant formation and to locate the three breakpoints precisely. Our cytogenetically unbalanced epileptic patient carried a 20q deletion and 20p duplication, and the genes, CHRNA4 and KCNQ2 that have been implicated in autosomal dominant epilepsy, were deleted. The haplo-insufficiency of these two genes may contribute to the cause of epilepsy in patients with ring chromosome 20.

22q11.2 duplication syndrome: two new familial cases with some overlapping features with DiGeorge/velocardiofacial syndromes.

Twenty-one patients, including our two cases, with variable clinical phenotype, ranging from mild learning disability to severe congenital malformations or overlapping features with DiGeorge/velocardiofacial syndromes (DG/VCFS), have been shown to have a chromosome duplication 22q11 of the region that is deleted in patients with DG/VCFS. The reported cases have been identified primarily by interphase FISH and could have escaped identification and been missed by routine cytogenetic analysis. Here we report on two inherited cases, referred to us, to rule out 22q11 microdeletion diagnosis of VCFS. The first patient was a 2-month-old girl, who presented with cleft palate, minor dysmorphic features including short palpebral fissures, widely spaced eyes, long fingers, and hearing loss. Her affected mother had mild mental retardation and learning disabilities. The second patient was a 7(1/2)-year-old boy with velopharyngeal insufficiency and mild developmental delay. He had a left preauricular tag, bifida uvula, bilateral fifth finger clinodactyly, and bilateral cryptorchidism. His facial features appeared mildly dysmorphic with hypertelorism, large nose, and micro/retrognathia. The affected father had mild mental retardation and had similar facial features. FISH analysis of interphase cells showed three TUPLE1-probe signals with two chromosome-specific identification probes in each cell. FISH analysis did not show the duplication on the initial testing of metaphase chromosomes. On review, band q11.2 was brighter on one chromosome 22 in some metaphase spreads. The paucity of reported cases of 22q11.2 microduplication likely reflects a combination of phenotypic diversity and the difficulty of diagnosis by FISH analysis on metaphase spreads. These findings illustrate the importance of scanning interphase nuclei when performing FISH analysis for any of the genomic disorders.

Characterization of cystic fibrosis conductance transmembrane regulator gene mutations and IVS8 poly(T) variants in Portuguese patients with congenital absence of the vas deferens.

BACKGROUND: Cystic fibrosis conductance transmembrane regulator (CFTR) gene mutations and IVS8 poly(T) variants in Portuguese patients with bilateral (CBAVD) and unilateral (CUAVD) congenital absence of the vas deferens remain to be evaluated. METHODS: Patient screening was carried out by PCR, denaturing gradient gel electrophoresis and DNA sequencing. RESULTS: CFTR mutations were found in 18 out of 31 (58.1%) CBAVD and in three of four (75%) CUAVD patients. The most frequent mutations were F508del and R334W in CBAVD and G542X in CUAVD, with the allelic frequencies of R334W (6.5%) and G542X (25%) being particular to the Portuguese population. The 5T allelic frequency was 3.5% in the fertile male population, 25% in CUAVD and 27.4% in CBAVD patients. The combined frequency of mutations (CFTR+5T) was increased in CBAVD to 22 out of 31 (71%). The frequency of CFTR mutations was compared with that of patients with secondary obstructive azoospermia (OAZ; one out of 16, 6.3%) and non-obstructive azoospermia (NOAZ; two out of 22, 9.1%) with conserved spermatogenesis, which were similar to the general population. However, whereas the 5T allelic frequency in OAZ was similar to that of the general population (3.1%), it was increased in NOAZ cases (14.3%). CONCLUSIONS: Data confirm that CFTR+5T mutations represent the most common genetic abnormality in CAVD, and suggest that cases of NOAZ may be associated with the 5T allele.

Functional disomy of Xp including duplication of DAX1 gene with sex reversal due to t(X;Y)(p21.2;p11.3).

Translocations involving the short arms of the X and Y in human chromosomes are uncommon. One of the best-known consequences of such exchanges is sex reversal in 46,XX males and some 46,XY females, due to exchange in the paternal germline of terminal portions of Xp and Yp, including the SRY gene. Translocations of Xp segments to the Y chromosome result in functional disomy of the X chromosome with an abnormal phenotype and sex reversal if the DSS locus, mapped in Xp21, is present. We describe a 7-month-old girl with severe psychomotor retardation, minor anomalies, malformations, and female external genitalia. Cytogenetic analysis showed a 46,X,mar karyotype. The marker was identified as a der(Y)t(Xp;Yp) by fluorescence in situ hybridisation analysis. Further studies with specific locus probes of X and Y chromosomes made it possible to clarify the break points and demonstrated the presence of two copies of the DAX1 gene, one on the normal X chromosome and one on the der(Y). The karyotype of the child was: 46,X,der(Y)t(X;Y)(p21.2;p11.3). The syndrome resulted from functional disomy Xp21.2-pter, with sex reversal related to the presence of two active copies of the DAX1 gene located in Xp21. Few cases of Xp disomy with sex reversal have been reported, primarily related to Xp duplications with 46,XY karyotype, and less often to Xp;Yq translocations. To our knowledge, our patient with sex reversal and a t(Xp;Yp) is the second reported case.