Analphoid 3qter markers

Two cases of marker chromosomes derived from a non‐centromeric location were studied to determine the characteristics of these markers with respect to the presence of functional centromeres and whether an associated phenotype could be described. The markers were characterized by fluorescence in situ hybridization and centromeric protein studies. Assessments were done to identify clinical features. Case 1 is a girl referred at age 1.5 years with swirly areas of hyperpigmentation, bilateral preauricular pits, hypotonia, developmental delay, and seizures. Case 2 is a male first evaluated as a newborn and then later during the first year of life. He had streaky hypopigmentation, right preauricular pit, accessory nipples, postaxial polydactyly, asymmetric cerebral ventricles, duplicated right kidney, a right pulmonary artery stenosis, and seizures. Mosaicism for an extra marker from the 3qter region was present in both cases. Both markers had a constriction near one end and were C‐band negative. Centromeric protein studies indicated absence of CENP‐B, presence of CENP‐C (data for case 1 only), and presence of CENP‐E. Marker chromosomes were thus identified with a chromosomal origin far from their usual centromeric region and yet appeared to have functional centromeres. These two cases did not permit a specific clinical phenotype to be ascribed to the presence of tetrasomy for 3q26.2 ∼ 3q27.2→3qter. Am. J. Med. Genet. 94:113–119, 2000. © 2000 Wiley‐Liss, Inc.     

Trisomy 6qter

A previously reported patient with trisomy for the distal part of 6q was shown by R-banding to be trisomic for 6q26qter, due to a t(6;22)(q26;p12) mat. Altogether nine patients with 6qter trisomy have been reported. The main features of the 6qter trisomy syndrome are: severe mental and growth retardation; acrocephaly and brachycephaly; a carp-shaped mouth; micrognathia; a very short neck with unusual anterior webbing; joint contractures; the absence of severe inner organ malformations; and survival into adulthood.     

Phenotype resembling Donnai-Barrow syndrome in a patient with 9qter;16qter unbalanced translocation

We describe a 3-year-old boy with complete agenesis of corpus callosum, developmental delay/mental retardation, anterior diaphragmatic hernia, Morgagni type, severe hypermetropia, and facial dysmorphism suggesting the diagnosis of Donnai-Barrow syndrome. Subtelomeric FISH analysis revealed a paternally-derived t(9;16) (q34.3;q24.3) translocation with partial 9q monosomy and partial 16q trisomy. As some facial features resemble the 9q emerging phenotype, we suggest the hypothesis that some patients with Donnai-Barrow syndrome might be abscribed to 9q terminal deletion.     

Duplication 3q(q21 → qter) without limb anomalies

We report on a 2.5-month-old boy with hypertelorism, hypertrichosis, anteverted nostrils, malformed ears, thin lips, downturned corners of the mouth, micrognathia, short neck, cryptorchidism, and bilateral simian creases without limb anomalies. Cytogenetic studies showed a duplication 3q → qter 46,XY,der(6),t(3;6)(q21;p25)pat. The absence of limb anomalies is noteworthy; all 12 previously reported patients with the same duplication had limb anomalies. The uniqueness of this report provokes speculations regarding limb morphogenesis in embryos with chromosome anomalies. The concepts of chronogenetics, heterochrony, and developmental field defects appear relevant to yet another set of patients with chromosome anomalies.     

A new case of dup(3q) syndrome due to a pure duplication of 3qter

The characteristic clinical features of the dup(3q) syndrome include typical facial features, mental and growth retardation, and (often) congenital heart anomalies. However, pure duplication of 3qter is rare because most of the reported cases are patients who carry an unbalanced translocation and, in addition to the duplication for 3qter, have a deletion for another chromosomal segment. A new case with a pure duplication of 3q detected in a 2-month-old boy is presented here. Extensive cytogenetic analysis revealed an inverted duplication of the distal part of 3q (chromosomal band 3q26.3 up to the telomere), with no (detectable) loss of the original telomeric sequences. Clinical evaluation revealed several phenotypic hallmarks characteristic for the dup(3q) syndrome. By comparing the duplicated region of this patient with the duplicated regions of the other patients with a pure duplication of 3q, we were able to localize the critical region for the dup(3q) phenotype to band 3q26.3. Alongside this new case with a pure duplication of 3q, an overview of six previous cases is given.     

A further case of monosomy 10qter

A child with a terminal deletion of chromosome 10 (q26) is described. A comparison of the phenotypic and cytogenetic features is made in the five reported cases of monosomy 10qter. No phenotypic features are found sufficiently characteristic to delineate a syndrome. Enzymatic activities for PGAMA and GOT1 were normal.     

Familial cryptic translocation between chromosomes 2qter and 8qter: further delineation of the Albright hereditary osteodystrophy-like phenotype

Recently five patients with an Albright hereditary osteodystrophy (AHO)-like phenotype were reported to have a subtelomeric deletion of the long arm of chromosome 2. These patients showed a striking resemblance to a number of patients from a large pedigree known to us for a long time. After molecular confirmation of a subtelomeric deletion in one patient, FISH analysis was used and a cryptic translocation between the long arms of chromosomes 2 and 8, t(2;8)(q37.3;q24.3), was detected. Remarkably, five proven and 10 probable cases with a 2qter deletion were found in the family, but none with an 8qter deletion. This was not explained by increased fetal loss. The major clinical characteristics of terminal 2q deletion are a short, stocky build, round face, sparse hair, deeply set eyes, bulbous nose, thin vermilion border, brachymetaphalangism, seizures, and developmental delay. A specific behavioural phenotype consisting of periods of hyperkinesia and aggression can develop with age. The overall phenotype is sufficiently characteristic to allow clinical recognition. The cytogenetic and molecular studies did not narrow down the common deleted region. Both testing of additional 2q markers and characterisation of other AHO-like patients with 2q37 microdeletions may help to define the candidate gene region.     

Delineation of the cryptic 1qter deletion phenotype

The 1qter microdeletion is often reported in the literature as a part of a complex chromosome rearrangement. We describe a patient with a normal initial cytogenetic analysis later found by subtelomeric FISH to have a de novo isolated 1qter microdeletion. Further characterization was completed through microarray comparative genomic hybridization (CGH) and specific bacterial artificial chromosomes (BACs) to a region of 5.2-5.3 Mbp. Six additional cases were reviewed from a literature search. While no particular feature is specifically unique, the most frequently associated features include short stature, developmental delay and mental retardation, microcephaly, seizures, abnormal corpus callosum, and abnormal ear shape. This further delineates the phenotype and further narrows the chromosomal region responsible for a 1qter microdeletion phenotype.     

Duplication of 7q31.2----7qter and deficiency of 18qter: report of two patients and literature review

We describe two male patients with a 46,XY,-18,+der(18),t(7;18) (q31.2;q23)mat karyotype. Previously, 22 other patients with dup(7q) have been described, but only four of them had duplication of segment 7q31----7qter. The two patients in this study were ascertained independently and lived in different states. However, because of the rarity of this translocation, the patients were suspected to be related. The families were investigated extensively, and the patients were found to be third cousins once removed. Both patients had severe hypospadias, large fontanelles, cleft palate, and minor facial anomalies (square and prominent forehead, short, downslanting palpebral fissures, long eyelashes, long philtrum, short nose, thin vermilion border with downcurved upper lip). Their phenotypes were compared with those of previously described patients. One of the two patients described here is alive at 23 months and is the oldest known living patient with this chromosome abnormality. Apneic spells often are present and may be secondary to severe brain abnormalities, such as those identified in our two patients.     

Monosomy 10qter: a new case.

A new case of terminal deletion 10q26-qter is described. The phenotypic features are compatible with those of the previously reported cases. Deafness is reported for the first time.     

Is there a monosomy 10qter syndrome?

A case of terminal deletion 10q25→qter is reported. Comparison of the findings with those noted in the three previously published cases revealed marked clinical dissimilarities and some unusual features not hitherto described.     

The Facioscapulohumeral muscular dystrophy region on 4qter and the homologous locus on 10qter evolved independently under different evolutionary pressure

Background  

The homologous 4q and 10q subtelomeric regions include two distinctive polymorphic arrays of 3.3 kb repeats, named D4Z4. An additional BlnI restriction site on the 10q-type sequence allows to distinguish the chromosomal origin of the repeats. Reduction in the number of D4Z4 repeats below a threshold of 10 at the 4q locus is tightly linked to Facioscapulohumeral Muscular Dystrophy (FSHD), while similar contractions at 10q locus, are not pathogenic. Sequence variations due to the presence of BlnI-sensitive repeats (10q-type) on chromosome 4 or viceversa of BlnI-resistant repeats (4q-type) on chromosome 10 are observed in both alleles.     

Trisomy 18qter and trisomy mapping of chromosome 18

Four cases of partial trisomy 18q are reported and compared to observations from the literature. The phenotype of 18qter trisomy is described and compared to full trisomy 18.