Abnormal childhood phenotypes associated with the same balanced chromosome rearrangements as in the parents

A case of Baraitser-Winter syndrome with unusual brain MRI findings: pachygyria, subcortical-band heterotopia, and periventricular heterotopia

Baraitser-Winter syndrome (BaWS) is characterized by iris coloboma, ptosis, hypertelorism, and mental retardation; it is a rare multiple congenital anomaly or a mental-retardation syndrome of unknown etiology. Patients suffering from this syndrome have been also found to show brain anomalies such as pachygyria, subcortical-band heterotopia (SBH), and hippocampal malformations; therefore, these anomalies have been included in the phenotypic spectrum of this syndrome. We report the case of a Japanese boy suffering from BaWS; the patient's brain magnetic resonance imaging scan revealed pachygyria, SBH, and periventricular heterotopia. However, the results of the genome-wide array comparative genomic hybridization did not reveal any chromosomal rearrangements.

Balanced translocations in mental retardation

Over the past few decades, the knowledge on genetic defects causing mental retardation has dramatically increased. In this review, we discuss the importance of balanced chromosomal translocations in the identification of genes responsible for mental retardation. We present a database-search guided overview of balanced translocations identified in patients with mental retardation. We divide those in four categories: (1) balanced translocations that helped to identify a causative gene within a contiguous gene syndrome, (2) balanced translocations that led to the identification of a mental retardation gene confirmed by independent methods, (3) balanced translocations disrupting candidate genes that have not been confirmed by independent methods and (4) balanced translocations not reported to disrupt protein coding sequences. It can safely be concluded that balanced translocations have been instrumental in the identification of multiple genes that are involved in mental retardation. In addition, many more candidate genes were identified with a suspected but (as yet?) unconfirmed role in mental retardation. Some balanced translocations do not disrupt a protein coding gene and it can be speculated that in the light of recent findings concerning ncRNA's and ultra-conserved regions, such findings are worth further investigation as these potentially may lead us to the discovery of novel disease mechanisms.

The phenotypic spectrum of baraitser-winter syndrome: a new case and review of literature

The syndrome of iris coloboma, ptosis, hypertelorism, and mental retardation (Online Mendelian Inheritance in Man -- OMIM # 243310), also known as the Baraitser-Winter syndrome, originally was described in a brother and sister and in an unrelated girl in 1988. Six additional individuals with a similar phenotype have been reported in the world literature. Microphthalmos, microcornea, and brain malformations were added to the phenotypic spectrum of this syndrome in 1995. We report a child who presented with the aforementioned findings. Eye examination revealed bilateral microphthalmos and typical iris, optic nerve, and choroidal colobomas. Magnetic resonance imaging of the brain demonstrated pachygyria and cortical atrophy.

Previously apparently undescribed syndrome: shallow orbits, ptosis, coloboma, trigonocephaly, gyral malformations, and mental and growth retardation

We describe 2 children with severe ptosis, trigonocephaly, broad nasal bridge, and major brain malformation. A total of 8 children have been reported who share most of these findings. Two of the individuals have had identical pericentric inversions involving chromosome 2p12-q14. These cases appear to represent a unique malformation syndrome.

"Balanced" karyotypes in six abnormal offspring of balanced reciprocal translocation normal carrier parents

Among 6800 consecutive blood samples studied for clinical cytogenetic diagnosis, we identified 30 families in which one parent of the proband had a balanced reciprocal autosomal translocation (excluding Robertsonian rearrangements). Twenty-eight of the 30 families had a malformed and/or mentally retarded proband: 19 with an unbalanced derived chromosome, 3 with abnormalities involving chromosomes other than those in the translocation, 5 with a "balanced" reciprocal translocation, and 1 with a normal karyotype. We hypothesize that the latter 6 affected probands with "balanced" karyotypes could be abnormal due to submicroscopic deletions and duplications as was originally suggested by Jacobs [1984]. Particularly in these 6 families, 83% of translocation breakpoints were associated with fragile sites, more than expected by chance (P < 0.025). This supports the report of an association between fragile sites and constitutional chromosome breakpoints by Hecht and Hecht [1984]. To explain these findings, we propose that autosomal fragile sites are unstable areas which predispose to breaks and unequal crossing over near the fragile site breakpoints creating minute duplications and deletions. Consequently, newborn infants inheriting a seemingly "balanced" karyotype from a normal parent with a balanced reciprocal translocation may still be at an increased risk of being malformed and/or developmentally delayed because of submicroscopic chromosomal imbalances.

Iris coloboma, ptosis, hypertelorism, and mental retardation: a new syndrome possibly localised on chromosome 2

A patient with a phenotype resembling that of three children recently reported is described. His karyotype shows a pericentric inversion of chromosome 2, very similar to another child previously reported. We discuss the possibility that all these cases constitute a distinct syndrome.

Familial mental retardation associated with balanced chromosome rearrangement rcp t(8;11)(q24.3;p15.1)

We report three sisters and their father with a reciprocal balanced translocation, rcp t(8;11)(q24.3;p15.1) and the same abnormal phenotypes, including mental retardation, growth disturbance, and amblyopia. It is considered that the abnormal phenotypes in our four cases might result from a tiny deletion or gene mutation at the breakpoints in 8q or 11p or both. Our cases showed no resemblance, apart from mental retardation, to Langer-Giedion syndrome, which is caused by the deletion of 8q23.3 and 8q24. Furthermore, our patients did not have the cardinal features of Beckwith-Wiedermann syndrome or WAGR which are caused by deletion of 11p. It is suggested that the amblyopia in our four cases might have resulted from the breakpoints at 11p15.1.

Clinical and cytogenetic survey of 39 individuals with Prader-Labhart-Willi syndrome

In a clinical and cytogenetic survey of 39 individuals with Prader-Labhart-Willi syndrome (PLWS) (23 males and 16 females ranging in age from 2 weeks to 39 years), an interstitial deletion of chromosome 15 (breakpoints q11 and q13) was identified in 21 cases and apparently normal chromosomes in the remainder. Studies of parental chromosome 15 variants showed that the del[15q] was paternal in origin, although chromosomes of both parents were normal. All chromosome deletions were de novo events. Possible causes for the chromosome deletion and the role of chromosome rearrangements in individuals with PLWS are discussed. Clinical characteristics of the deletion and nondeletion groups were recorded and compared with 124 individuals reported in the literature. Individuals with the chromosome deletion were found to have lighter hair, eye, and skin color, greater sun sensitivity, and higher intelligence scores than individuals with normal chromosomes. Correlation studies of metacarpophalangeal pattern profile variables and dermatoglyphic findings indicate apparent homogeneity of the deletion group and heterogeneity of individuals with PLWS and normal chromosomes.

The significance of pericentric inversions of chromosome 2

Thirteen new cases of a pericentric inversion 2 collected from different laboratories are reported. In addition 41 cases of a pericentric inversion 2 were reviewed from the literature. The pooled data were analysed using Weinberg's proband method to evaluate the risk of a carrier for either children with congenital anomalies or reproductive wastage. In the "corrected" sample of 166 lifeborn offspring of carriers of a pericentric inversion 2 there were five who showed phenotypic anomalies and two died a few hours after delivery. The reported anomalies are heterogeneous and probably reflect the basic risk of any couple for abnormal lifeborn offspring. There has been no observation of a lifeborn who inherited an unbalanced recombination of a parental pericentric inversion 2. A carrier of a pericentric inversion 2 obviously has an increased risk for reproductive wastage. This is indicated by (1) an increase of the rate of spontaneous abortions and (2) an increase of the rate of index patients ascertained because of previous miscarriages. The risk of a carrier of a pericentric inversion 2 for a spontaneous abortion or a stillbirth may be about twice the basic risk of the general population.

Inversion of chromosome 2 (p11p13): frequency and implications for genetic counselling

Two cases of a pericentric inversion of chromosome 2 were found amongst 3619 blood specimens referred for karyotypic analysis. An additional three cases were identified within 1820 pregnancies presenting for genetic amniocentesis because of late maternal age. The implications for management in these cases are discussed.

Familial paracentric inversion of chromosome 15 (q15q24)

A paracentric inversion of chromosome 15 was observed in the father of two infants who died 29 days and 24 hours, respectively, after birth. The same inversion was found in two sisters of the proband.

Pericentric inversions. Problems and significance for clinical genetics

A review is given of the incidence, cytogenetics, and biologic relevance of pericentric inversions (pii). In 251 cases in the literature and our patients, 96 different inversion forms with different breakpoints are found. Eighteen of these cases have been observed several times in unrelated families; they are classified as types. The problem of pii in the heterochromatic regions of chromosomes 1 and 9 is especially emphasized and the investigations required are pointed out. The significance of the individual pii is checked with regard to their behavior in meiosis and their phenotypical relevance. An approximately 1:1 segregation is found. Fertility, stillbirth, and rates of abortion are not statistically altered. The gonadal findings available at present in man are reported and commented on. The occurrence of aneusomic recombinants among the live offspring of carriers shows a marked dependence on the length of the relative inversion segments. Since these are distinctly below average in inversion types, they only result in recombinants in exceptional cases. Certain pointers to an above-random common occurrence of other chromosomal aberrations are not found in families with pii. A correlation between pii and clinical symptoms likewise cannot be detected. However, in this connection it is pointed out that trisomic mosaics were observed jointly with pii(9) and pii(22). The review is completed by a brief examination of the literature concerning the significance of pii in evolution.

Mentally retarded siblings with congenital heart defect, peculiar facies and cryptorchidism in the male: possible McDonough syndrome with coincidental (X; 20) translocation

We report on a family in which two of the three children (girl and boy) have a MCA/MR syndrome consisting of peculiar facies, retarded psychomotor development, mental retardation, congenital heart defect, kyphoscoliosis, diastasis recti, and cryptorchidism in the boy. This syndrome is quite similar to that of the only family previously described and which was denominated McDonough Syndrome. The syndrome is delineated and autosomal recessive inheritance is suggested as the most likely etiology. A balanced translocation (X; 20) in the affected boy and in the unaffected mother was a coincidental finding.

Hereditary persistence of fetal haemoglobin (HPFH) in conjunction with a chromosomal translocation involving the haemoglobin beta locus

An HPFH syndrome was found in a woman and her daughter who also carry a 'balanced' cyclic translocation of chromosome segments involving four chromosomes, with one break point located in the region of the Hb beta locus. This HPFH is characterized by 5% and 8% Hb F in peripheral blood, uneven distribution of Hb F in the red cells, and a G gamma/G gamma + A gamma ratio of 0.4. The mapping of the non alpha gene cluster shows no detectable deletion in the entire gamma-delta-beta-globin gene region.

Fragile chromosome 16(q22) cause a balanced translocation at the same point

A father with a fragile 16(q22) has a son with a de novo balanced translocation 1;16. Both the fragile site and the break point at chromosome 16 are similar (q22). The question of whether the fragile site can cause a structural chromosome abnormality at the same point is discussed.

Multiple skeletal familial abnormalities associated with balanced reciprocal translocation 2;8(q32;p13)

A father and three of his offspring had skeletal abnormalities consisting of a short forearm, cubitus valgus, fusion of first and second cervical vertebrae, and cleft of L5 and S1. All four had a reciprocal, apparently balanced, translocation 2;8(q32;p13). Normal sibs had normal chromosomes. We conclude that this may be a rare instance of an autosomal dominant condition associated with a balanced chromosome translocation.

Prader-Willi syndrome and chromosome 15. A clinical discussion of 20 cases

A chromosome 15 anomaly was observed in 12 of 20 patients, 17 of whom were clinically suspected of having Prader-Willi syndrome (PWS). The clinical features of eight cases with 15q11-12 deletion were very similar to those originally described in PWS. On the other hand, the group of normal karyotype patients is heterogeneous, and their features do not strictly correspond to the clinical definition of PWS. However, the hypothesis that PWS is associated with deletion of 15q11-12 can neither explain the apparently balanced translocations of chromosome 15 nor account for the small supernumerary metacentric chromosomes corresponding to an isochromosome 15 for band 15q11 observed in some cases.

Franceschetti syndrome in a child with a de novo balanced translocation (5;13)(q11;p11) and significant decrease of hexosaminidase B

We report a previously undescribed case of a de novo balanced translocation t(5;13)(q11;p11) and Franceschetti syndrome in a 3-year-old girl. The hypothesis that this unusual association might not be coincidental but rather due to position effect is proposed. Moreover the significant decrease of hexosaminidase B activity suggests the localization of this gene on the 5q11 band.

Unexpected structural chromosome rearrangements in prenatal diagnosis

Among 5315 prenatal diagnoses performed for various indications (maternal age, neural tube defect, metabolic diseases, X-linked diseases, pathologic pregnancies) 29 unexpected structural chromosome rearrangements were found in fetal cells. Fourteen were de novo chromosome rearrangements, six unbalanced, and eight balanced. Fifteen were inherited and balanced rearrangements. This high frequency of structural anomalies is discussed.

A recognizable phenotype in a child with partial duplication 13q in a family with t(10q;13q)

A case of partial duplication 13q14 leads to qter is reported in a 9-year-old male with clinical symptoms which include trigonocephaly and synophrys, producing an easily identifiable phenotype. The chromosome duplication resulted from a familial t(10;13)(qtr;q14). Subsequently, a normal balanced carrier sibling was diagnosed prenatally.

Study on segregation and risk for abnormal offspring in carriers of pericentric inversion of the (p11 leads to q13) segment of chromosome 2

Pericentric inversion of chromosome 2 was detected in four unrelated families. All these inversions involved the segment p11 leads to q13. The pedigree data are considered in comparison with other cases reported in the literature. Segregation data and possible reproductive failures are discussed.

Partial trisomy 4 resulting from a complex maternal rearrangement of chromosomes 2, 4, and 18 with interstitial translocation

A woman presented a complex chromosome rearrangement with translocation between chromosome 2 and 4 in addition to an insertion of the band 4q12 leads to q13 in the long arm of chromosome 18. The authors present a case study of the daughter who displayed the abnormal chromosome 18 and trisomy of band 4q12 leads to q13.

Pericentric inversion in chromosome no. 2 as a de novo mutation

A patient with a de novo inversion of chromosome 2 is described. Two of her three children have the same inversion.