Atypical noncontiguous TSC2/PKD1 gene deletions presenting as tuberous sclerosis/polycystic kidney disease contiguous gene syndrome.

Tuberous sclerosis complex (TSC) and autosomal dominant polycystic kidney disease (ADPKD) are genetically distinct disorders typically associated with pathogenic variants in TSC1 and TSC2 for the former and PKD1 and PKD2 for the latter. TSC2 and PKD1 lie adjacent to each other, and large deletions comprising both genes lead to TSC2/PKD1 contiguous gene deletion syndrome (CGS). In this study, we describe a young female patient exhibiting symptoms of TSC2/PKD1 CGS in which genetic analysis disclosed two noncontiguous partial gene deletions in TSC2 and PKD1 that putatively are responsible for the manifestations of the syndrome. Further analysis revealed that both deletions appear to be de novo on the maternal chromosome, presumably with a germline origin. Despite extensive analysis, no maternal chromosomal rearrangement triggering these pathogenic variants was detected. This case elucidates a unique pathogenesis for TSC2/PKD1 CGS, diverging from the common contiguous deletions typically observed, marking the first reported instance of TSC2/PKD1 CGS caused by independent, functionally significant partial gene deletions.

dup(1)(q21q32) as a sole cytogenetic event is associated to a leukemic transformation in myelodysplastic syndromes.

Duplication of the long arm of chromosome 1 (1q) has been detected accompanied with other chromosome abnormalities in Myelodysplastic Syndromes (MDS). However, as a sole karyotypic change, it is rarely observed. We present here two patients affected of a MDS that showed a dup(1)(q21q32) as a sole cytogenetic change in their bone marrow cells. Complementary methodologies confirmed the duplication of chromosome 1q and, did not show additional cryptic chromosome abnormalities. One patient acquired a secondary trisomy 8 and the other one progressed toward an acute leukemia with no additional cytogenetic alterations.

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.

Mutations in TBX1 genocopy the 22q11.2 deletion and duplication syndromes: a new susceptibility factor for mental retardation.

A screen for TBX1 gene mutations identified two mutations in patients with some features compatible with the 22q11.2-deletion syndrome but with no deletions. One is a de novo missense mutation and the other is a 5' untranslated region (5'UTR) C>T change that affects a nucleotide with a remarkable trans-species conservation. Computer modelling shows that the 5'UTR change is likely to affect the mRNA structure and in vitro translation experiments demonstrate that it produces a twofold increase in translation efficiency. Recently, duplications in the 22q11.2 region were reported in patients referred for fragile-X determination because of cognitive and behavioural problems. Because the 5'UTR nucleotide change may be a functional equivalent of a duplication of the TBX1 gene, we decided to screen 200 patients who had been referred for fragile-X determination and 400 healthy control individuals. As a result, we found the 5'UTR mutation to be present in three patients with mental retardation or behavioural problems and absent in control individuals of the same ethnic background. This observation suggests that it may be reasonable to screen for such mutation among patients with unspecific cognitive deficits and we provide an easy and quick way to do it with an amplification refractory mutation system (ARMS) approach. To our knowledge, this is the first human mutation showing that TBX1 is a candidate causing mental retardation associated with the 22q11.2 duplication syndrome.

Spontaneous repigmentation of silvery hair in an infant with congenital hydrops fetalis and hypoproteinemia.

Silvery hair is a characteristic finding of 3 rare autosomal recessive disorders: Chédiak-Higashi syndrome (CHS), Elejalde syndrome (ES), and Griscelli syndrome (GS). We report the case of a 2-month-old male infant with transient silvery hair and generalized hypopigmentation of the skin and eyes who did not have one of these classic causative disorders. The patient was delivered at 35 weeks' gestation with congenital hydrops fetalis associated with a chromosomal abnormality (46,XY,add[2],[p23]), hypothyroidism, hypoproteinemia, and hypogammaglobulinemia. Over the course of follow-up, spontaneous brown repigmentation of the silvery hair was noted. We concluded that the silvery hair was induced by hypoproteinemia secondary to congenital hydrops fetalis.