Nance-Horan syndrome in females due to a balanced X;1 translocation that disrupts the NHS gene: Familial case report and review of the literature.

The Nance-Horan syndrome is an X-linked disorder characterized by congenital cataract, facial features, microcornea, microphthalmia, and dental anomalies; most of the cases are due to NHS gene mutations on Xp22.13. Heterozygous carrier females generally present less severe features, and up to 30% of the affected males have intellectual disability. We describe two patients, mother and daughter, manifesting Nance-Horan syndrome. The cytogenetic and molecular analyses demonstrated a 46,X,t(X;1)(p22.13;q22) karyotype in each of them. No copy-number genomic imbalances were detected by high-density microarray analysis. The mother had a preferential inactivation of the normal X chromosome; expression analysis did not detect any mRNA isoform of NHS. This is the first report of Nance-Horan syndrome due to a skewed X chromosome inactivation resulting from a balanced translocation t(X;1) that disrupts the NHS gene expression, with important implications for clinical presentation and genetic counseling.

Cytogenetic profile in 1,921 cases of trisomy 21 syndrome.

BACKGROUND AND AIMS: Trisomy 21 is the most frequent genetic cause of intellectual disability. It is caused by different cytogenetic aberrations: free trisomy, Robertsonian translocations, mosaicism, duplication of the critical region and other structural rearrangements of chromosome 21. The aim of the study was to identify in Mexican trisomy 21 patients who attended Hospital Infantil de México Federico Gómez from 1992-2011 the type and frequency of the cytogenetic aberration and to evaluate the effect of maternal age. METHODS: A retrospective analysis of epidemiological data and karyotype reports were carried out; type and frequency of the cytogenetic variants were determined. RESULTS: We identified 2,018 cases referred with a clinical diagnosis of trisomy 21. In 1,921 analyses (95.2%) a cytogenetic variant of trisomy 21 was identified: free trisomy 21 in 1,787 cases (93.02%), four cases (0.21%) had an additional non-contributory aberration; Robertsonian translocations in 92 cases (4.79%); mosaicism in 31 cases (1.61%) and seven cases (0.36%) had other chromosomal abnormalities, five (0.26%) had other contributory structural rearrangements and two corresponded to double aneuploidies (0.10%). Gender distribution was 1,048 (54.56%) males and 873 (45.44%) females. A maternal age effect was observed in patients with free trisomy 21 with mothers >36 years of age. CONCLUSION: The present work reports the experience of a Mexican referral center regarding the karyotype diagnosis of patients with trisomy 21 and is one of the most extensive studies published so far. Percentages of the cytogenetic abnormalities present in our population reflect the ones previously reported for these cytogenetic alterations worldwide.

Velocardiofacial syndrome in Mexican patients: Unusually high prevalence of congenital heart disease.

INTRODUCTION: Velocardiofacial syndrome (VCFS) is the most common microdeletion syndrome with an incidence of 1:4000 live births. Its phenotype is highly variable with facial, velopharyngeal, cardiac, endocrine, immunologic and psychiatric abnormalities. It is caused by a microdeletion in chromosome 22q11.2. OBJECTIVES: We present 7 years of experience evaluating patients with VCFS regarding their main clinical characteristics. MATERIAL AND METHODS: The patients included were multidisciplinary evaluated and had a positive FISH analysis for del22q11.2. RESULTS: A total of 62 patients were assessed, a 34 female/28 male ratio was observed with ages ranging from 9 days to 16 years, all but one patient had typical facial features. A diagnosis of congenital heart disease was established in 97% of the patients; other clinical characteristics were identified with different percentages such as cleft palate, and hypocalcaemia. Three cases had a familial presentation. DISCUSSION: While the clinical findings of this study were in general terms in keeping with the literature, it is interesting the unexpectedly high percentage of congenital heart disease identified in Mexican children with VCFS that also was the main cause for clinical referral.

Trisomy 1q41-qter and monosomy 3p26.3-pter in a family with a translocation (1;3): further delineation of the syndromes.

BACKGROUND: Trisomy 1q and monosomy 3p deriving from a t(1;3) is an infrequent event. The clinical characteristics of trisomy 1q41-qter have been described but there is not a delineation of the syndrome. The 3p25.3-pter monosomy syndrome (MIM 613792) characteristics include low birth weight, microcephaly, psychomotor and growth retardation and abnormal facies. CASE PRESENTATION: A 2 years 8 months Mexican mestizo male patient was evaluated due to a trisomy 1q and monosomy 3p derived from a familial t(1;3)(q41;q26.3). Four female carriers of the balanced translocation and one relative that may have been similarly affected as the proband were identified. The implicated chromosomal regions were defined by microarray analysis, the patient had a trisomy 1q41-qter of 30.3 Mb in extension comprising about 240 protein coding genes and a monosomy 3p26.3-pter of 1.7 Mb including only the genes CNTN6 (MIM 607220) and CHL1 (MIM 607416), which have been implicated in dendrite development. Their contribution to the phenotype, regarding the definition of trisomy 1q41-qter and monosomy 3p26.3-pter syndromes are discussed. CONCLUSION: We propose that a trisomy 1q41-qter syndrome should be considered in particular when the following characteristics are present: postnatal growth delay, macrocephaly, wide fontanelle, triangular facies, frontal bossing, thick eye brows, down slanting palpebral fissures, hypertelorism, flat nasal bridge, hypoplasic nostrils, long filtrum, high palate, microretrognathia, ear abnormalities, neural abnormalities (in particular ventricular dilatation), psychomotor developmental delay and mental retardation. Our patient showed most of these clinical characteristics with exception of macrocephaly, possibly due to a compensatory effect by haploinsufficiency of the two genes lost from 3p. The identification of carriers has important implications for genetic counseling as the risk of a new born with either a der(3) or der(1) resulting from an adjacent-1 segregation is of 25% for each of them, as the products of adjacent-2 or 3:1 segregations are not expected to be viable.