Takaya Tohma

Molecular cytogenetic analysis of eight inversion duplications of human chromosome 13q that each contain a neocentromere.

Neocentromeres are fully functional centromeres that have arisen in previously noncentromeric chromosomal locations on rearranged chromosomes. The formation of neocentromeres results in the mitotic stability of chromosomal fragments that do not contain endogenous centromeres and that would normally be lost. Here we describe a unique collection of eight independent patient-derived cell lines, each of which contains a neocentromere on a supernumerary inversion duplication of a portion of human chromosome 13q. Findings in these patients reveal insight into the clinical manifestations associated with polysomy for portions of chromosome 13q. The results of FISH and immunofluorescent analysis of the neocentromeres in these chromosomes confirm the lack of alpha-satellite DNA and the presence of CENtromere proteins (CENP)-C, -E, and hMAD2. The positions of the inversion breakpoints in these chromosomes have been placed onto the physical map of chromosome 13, by means of FISH mapping with cosmid probes. These cell lines define, within chromosome 13q, at least three distinct locations where neocentromeres have formed, with five independent neocentromeres in band 13q32, two in band 13q21, and one in band 13q31. The results of examination of the set of 40 neocentromere-containing chromosomes that have thus far been described, including the 8 neocentromere-containing chromosomes from chromosome 13q that are described in the present study, suggest that chromosome 13q has an increased propensity for neocentromere formation, relative to some other human chromosomes. These neocentromeres will provide the means for testing hypotheses about sequence requirements for human centromere formation.

SMOC1 is essential for ocular and limb development in humans and mice.

Microphthalmia with limb anomalies (MLA) is a rare autosomal-recessive disorder, presenting with anophthalmia or microphthalmia and hand and/or foot malformation. We mapped the MLA locus to 14q24 and successfully identified three homozygous (one nonsense and two splice site) mutations in the SPARC (secreted protein acidic and rich in cysteine)-related modular calcium binding 1 (SMOC1) in three families. Smoc1 is expressed in the developing optic stalk, ventral optic cup, and limbs of mouse embryos. Smoc1 null mice recapitulated MLA phenotypes, including aplasia or hypoplasia of optic nerves, hypoplastic fibula and bowed tibia, and syndactyly in limbs. A thinned and irregular ganglion cell layer and atrophy of the anteroventral part of the retina were also observed. Soft tissue syndactyly, resulting from inhibited apoptosis, was related to disturbed expression of genes involved in BMP signaling in the interdigital mesenchyme. Our findings indicate that SMOC1/Smoc1 is essential for ocular and limb development in both humans and mice.

Characterization of the gene encoding human pituitary-specific transcription factor, Pit-1

Pit-1 is a pituitary-specific transcription factor that binds to and transactivates promoters of growth hormone- and prolactin-encoding genes. A chromosomal gene related to human Pit-1 isolated from human gene libraries was over 14 kb long and split into six exons. All of the splice donor and acceptor sites conformed to the GT/AG rule. The gene was mapped to human chromosome region 3p11.

The origin of cytologically unidentifiable chromosome abnormalities: six cases ascertained by targeted chromosome-band painting.

De novo chromosome structural abnormalities cannot always be diagnosed by the use of standard cytogenetic techniques. We applied a previously developed chromosome-band-specific painting method to the diagnosis of such rearrangements. The diagnostic procedures consisted of microdissection of an aberrant chromosomal region of a given patient, polymerase chain reaction (PCR) amplification of the dissected chromosomal DNA, and subsequent competitive fluorescence in situ hybridization (FISH) using the PCR products as a probe pool on metaphase chromosomes from the patient and/or a karyotypically normal person. With this strategy, we studied 6 de novo rearrangements (6p+, 6q+, 9p+, 17p+, +mar, and +mar) in 6 patients. These rearrangements had been seen by conventional banding but their origin could not be identified. In all 6 patients, we successfully ascertained the origin. Using an aberrant region-specific probe pool, FISH signals appeared on both the aberrant region and a region of another specific chromosome pair. A reverse probe pool that was generated through the microdissection of normal chromosomes at a candidate region for the origin of the aberration hybridized with both the aberrant and the candidate regions. We thus diagnosed one patient with 17p+ as having trisomy for 14q32-qter, one with 9p+ as having trisomy for 12pter-p12, one with 6q+ as having a tandem duplication (trisomy) of a 6q23-q25 segment, one with 6p+ as having a tandem duplication (trisomy) of a 6p23-q21.3 segment, one with a supernumerary metacentric marker chromosome as having tetrasomy for 18pter-cen, and the last with an additional small marker chromosome as having trisomy for 18p11.1 (or p11.2)-q11.2. The present targeted chromosome-band-painting method provides the simple and rapid preparation of a probe pool for region-specific FISH, and is useful for the diagnosis of chromosome abnormalities of unknown origin.

Craniofacial and dental characteristics of Kabuki syndrome

We describe oral manifestations in six patients (three females and three males aged 6 to 24 years) with Kabuki syndrome (KS), based on their physical, orthopantomographic, and cephalometric findings. All six patients had a high-arched palate, malocclusion, most commonly unilateral posterior cross-bite (5/6), severe maxillary recession and mid-facial hypoplasia. Other frequently observed oral manifestations included small dental arch and hypodontia. Three patients lacked permanent teeth, mostly the central/lateral incisors. Both tooth size (in primary and permanent teeth) and dental arch (in length and width) tended to be small. We would like to stress that oral care and management is a must for the well-being of KS patients.

Functional disomy for Xq26.3-qter in a boy with an unbalanced t(X;21)(q26.3;p11.2) translocation

A nine-month-old boy, with functional disomy for Xq26-qter and multiple congenital abnormalities, is reported. The boy had severe pre- and postnatal growth retardation, profound developmental delay, hypotonia, microcephaly, agenesis of the corpus callosum, dysmorphic facial features, cryptorchidism, and left multidysplastic kidney. He developed feeding difficulties and infantile spasms. G-banding analysis of his chromosomes showed additional material on the short arm of chromosome 21. His parents refused to submit to chromosome analysis. Analysis with chromosome microdissection followed by reverse and forward chromosome painting indicated his karyotype as 46,XY,der(21)t(X;21)(q26;p11.2). This is the first description of pure functional disomy for Xq26-qter due to an unbalanced X-autosome translocation.

The costello syndrome: A boy with thick mitral valves and arrhythmias

SummaryA 3-year-old boy with Costello syndrome is reported. He had typical clinical features of the syndrome including severe postnatal growth retardation, poor sucking, mild developmental delay, a coarse characteristic facies, thick and loose skin of the hands and feet, sparse and curly hair, dark skin, and relative macrocephaly but lacked nasal papillomas. In addition, he had cardiac anomalies with extrasystoles and thick mitral valve tips. Mitral valve defects may be a clinical feature of the syndrome.

A locus for ophthalmo‐acromelic syndrome mapped to 10p11.23

Ophthalmo‐acromelic syndrome (OAS, OMIM %206920) is a rare autosomal recessive disease, presenting with clinical anophthalmia and limb anomalies. We recruited three OAS families including a Japanese family with two affected patients and two consanguineous Lebanese families each having an affected. Homozygosity mapping was performed using the 50K SNP chip and additional informative markers. A locus for OAS was mapped to the 422‐kb region at 10q11.23, based on the results from the two consanguineous families as well as the consistent data from the Japanese non‐consanguineous family. The 422‐kb region only contained one gene, MPP7. Although we could not detect any pathological mutations in OAS families analyzed, MPP7 could remain a candidate as aberrant changes might exist beyond our mutation detection methods. Further families are needed to confirm this candidate locus.

Two sisters with Toriello-Carey syndrome

Toriello-Carey syndrome comprises agenesis of the corpus callosum, telecanthus, short palpebral fissures, small nose with anteverted nares, Robin sequence, abnormally shaped ears, cardiac defect, and hypotonia. We describe two Japanese sisters with a Toriello-Carey syndrome whose phenotypes were as severe as reported male cases. The younger sister died suddenly at age 4 months. Our patients with a severe phenotype and possible parental consanguinity suggest autosomal recessive inheritance of Toriello-Carey syndrome.

Small interstitial deletion of the long arm of chromosome 2 (2q24.3): further delineation of 2q medial monosomy syndrome.

SummaryWe report on a female infant with an interstitial deletion involving 2q24.3. She had multiple congenital anomalies similar to those in patients with del(2)(q31q33) except for an occipital encephalocele. As a result of comparison of clinical findings among interstitial 2q deletions, a distinct 2q medial monosomy syndrome may be delineable in association with a deletion of 2q31.