A deletion and a duplication in distal 22q11.2 deletion syndrome region. Clinical implications and review.

BACKGROUND: Individuals affected with DiGeorge and Velocardiofacial syndromes present with both phenotypic diversity and variable expressivity. The most frequent clinical features include conotruncal congenital heart defects, velopharyngeal insufficiency, hypocalcemia and a characteristic craniofacial dysmorphism. The etiology in most patients is a 3 Mb recurrent deletion in region 22q11.2. However, cases of infrequent deletions and duplications with different sizes and locations have also been reported, generally with a milder, slightly different phenotype for duplications but with no clear genotype-phenotype correlation to date. METHODS: We present a 7 month-old male patient with surgically corrected ASD and multiple VSDs, and dysmorphic facial features not clearly suggestive of 22q11.2 deletion syndrome, and a newborn male infant with cleft lip and palate and upslanting palpebral fissures. Karyotype, FISH, MLPA, microsatellite markers segregation studies and SNP genotyping by array-CGH were performed in both patients and parents. RESULTS: Karyotype and FISH with probe N25 were normal for both patients. MLPA analysis detected a partial de novo 1.1 Mb deletion in one patient and a novel partial familial 0.4 Mb duplication in the other. Both of these alterations were located at a distal position within the commonly deleted region in 22q11.2. These rearrangements were confirmed and accurately characterized by microsatellite marker segregation studies and SNP array genotyping. CONCLUSION: The phenotypic diversity found for deletions and duplications supports a lack of genotype-phenotype correlation in the vicinity of the LCRC-LCRD interval of the 22q11.2 chromosomal region, whereas the high presence of duplications in normal individuals supports their role as polymorphisms. We suggest that any hypothetical correlation between the clinical phenotype and the size and location of these alterations may be masked by other genetic and/or epigenetic modifying factors.

Unrelated chromosomal anomalies found in patients with suspected 22q11.2 deletion.

Screening for 22q11.2 deletions has not an easy approach due to the wide variability of their associated phenotype. Many clinical features overlap with those of other known syndromes and reported loci. Patients referred to exclude a 22q11.2 deletion are usually tested with a locus-specific FISH probe, with 10% positive cases depending on the selection criteria, but patients testing negative for FISH at 22q11.2 may have other chromosomal aberrations in routine cytogenetic analysis. We tested 819 patients suspected of having a 22q11.2 deletion. Eighty-eight patients (10.7%) were positive for 22q11.2 deletion, whereas 30 patients (3.7%) showed other chromosomal abnormalities involving deletions and duplications, derivative chromosomes, marker chromosomes, apparently balanced and unbalanced translocations and sex chromosome aneuploidies. Of these alterations, 28 did not involve region 22q11 and most had not been associated with 22q11.2 deletion phenotype before. We discuss the similarity of DiGeorge/velocardiofacial syndrome with other known clinical entities and suggest correlations between the new loci and the observed clinical features. The frequency of unrelated chromosomal anomalies reported in this study and in other previous reports highlights the importance of conventional cytogenetic analysis as an initial genome-wide screening tool in all referred patients, and provides useful data to optimize diagnostic and screening protocols according to the most frequent chromosomal findings.

Mapping translocation breakpoints by next-generation sequencing.

Balanced chromosome rearrangements (BCRs) can cause genetic diseases by disrupting or inactivating specific genes, and the characterization of breakpoints in disease-associated BCRs has been instrumental in the molecular elucidation of a wide variety of genetic disorders. However, mapping chromosome breakpoints using traditional methods, such as in situ hybridization with fluorescent dye-labeled bacterial artificial chromosome clones (BAC-FISH), is rather laborious and time-consuming. In addition, the resolution of BAC-FISH is often insufficient to unequivocally identify the disrupted gene. To overcome these limitations, we have performed shotgun sequencing of flow-sorted derivative chromosomes using "next-generation" (Illumina/Solexa) multiplex sequencing-by-synthesis technology. As shown here for three different disease-associated BCRs, the coverage attained by this platform is sufficient to bridge the breakpoints by PCR amplification, and this procedure allows the determination of their exact nucleotide positions within a few weeks. Its implementation will greatly facilitate large-scale breakpoint mapping and gene finding in patients with disease-associated balanced translocations.

Mietens-Weber syndrome: two new patients and a review.

In 1966, Mietens and Weber reported four out of six siblings from a consanguineous couple with growth failure, dislocation of the head of the radii, bilateral flexion contracture of the elbows, short ulnae and radii, bilateral corneal opacities, horizontal and rotational nystagmus, strabismus, small, pointed nose and mild to moderate mental retardation. Since then, only three other cases have been reported. We report on two new cases, a pair of female twins aged 9 years. The patients were born after an uneventful, normal pregnancy, to young and non-consanguineous parents. After birth, physical findings included horizontal nystagmus and dislocation of both elbows because of abnormally short radii and ulnae in both twins. Further clinical examinations showed moderate psychomotor delay with marked language compromise. Karyotypes were normal in both girls. A review of the literature reveals that the Mietens-Weber syndrome is an uncommon disorder with a probable autosomal recessive pattern of inheritance. To our best knowledge, including the two cases reported here, only nine cases have been observed so far. The finding of congenital nystagmus and radii dislocation in a patient with mental retardation is probably nonrandom and is highly suggestive of Mietens-Weber syndrome.

Higher frequency of uncommon 1.5-2 Mb deletions found in familial cases of 22q11.2 deletion syndrome.

Familial 22q11.2 deletions have been reported as a 6%-28% of the total affected cases of 22q11.2 microdeletion syndrome (del22q11.2). Different deletion genotypes have been described for this disorder, with a predominant 3 Mb deletion present in 90% of the cases, a less common 1.5-2 Mb deletion in 8%, and atypical smaller deletions in 2%. We have studied 15 cases of del22q11.2 from 6 families (two of them three-generation families) that were previously diagnosed through FISH. We have sized the deleted region by allele genotyping of 12-16 polymorphic markers in all cases, and we have found three families affected with the 1.5-2 Mb deletion, two affected with the 3 Mb deletion, and one in which the deletion size could not be determined. This predominance of the smaller 1.5-2 Mb deletions in our familial cases differs from the minor frequency observed in sporadic cases of del22q11.2. This finding suggests that small deletions are more linked to familial inheritance than large ones, possibly due to psychosocial or biological factors associated with differences in the phenotype. Deletion sizing on routine diagnosis may help characterizing the inheritability of 22q11.2 microdeletion syndrome.

Macrocephaly-cutis marmorata telangiectatica congenita: report of six new patients and a review.

We report on six additional patients with macrocephaly-cutis marmorata telangiectatica congenita (M-CMTC; MIM 602501) and review the literature. This syndrome is a multiple congenital anomalies/mental retardation and overgrowth disorder comprising macrocephaly, cutis marmorata, vascular marks of lip and/or philtrum, syndactyly, hemihypertrophy, CNS anomalies, and developmental delay. Based on the findings in our 6 patients and on 69 patients previously reported we listed the very frequent (observed in >75%), frequent (25-75%), and less frequent (>25%) components of the syndrome.