PCR screening for 22q11.2 microdeletion: Development of a new cost-effective diagnostic tool

[22q11.2DS Syndrome as a Genetic Subtype of Schizophrenia]

INTRODUCTION

The 22q11.2 deletion syndrome (22q11.2DS) is associated with the microdeletion of this chromosomal region, and represents the second most common genetic syndrome after Down's syndrome. In patients with schizophrenia, 22q11.2DS has a prevalence of 2%, and in selected groups can be increased to between 32-53%.

OBJECTIVE

To describe the generalities of 22q11.2DS syndrome as a genetic subtype of schizophrenia, its clinical characteristics, molecular genetic aspects, and frequency in different populations.

METHODS

A review was performed from 1967 to 2013 in scientific databases, compiling articles about 22q11.2DS syndrome and its association with schizophrenia.

RESULTS

The 22q11.2 DS syndrome has a variable phenotype associated with other genetic syndromes, birth defects in many tissues and organs, and a high rate of psychiatric disorders, particularly schizophrenia. Likewise, it has been identified in clinical populations with schizophrenia selected by the presence of common syndromic characteristics. FISH, qPCR and MLPA techniques, and recently, aCGH and NGS technologies, are being used to diagnose this microdeletion.

CONCLUSIONS

It is important in clinical practice to remember that people suffering the 22q11.2DS have a high genetic risk for developing schizophrenia, and it is considered that the simultaneous presence of this disease and 22q11.2DS represents a genetic subtype of schizophrenia. There are clear phenotypic criteria, molecular and cytogenetic methods to diagnose this group of patients, and to optimize a multidisciplinary approach in their monitoring.

Molecular screening for 22Q11.2 deletion syndrome in patients with congenital heart disease

Few studies have investigated the prevalence of 22q11.2 deletion syndrome (22q11.2DS) among patients with isolated heart defects or nonconotruncal heart defects. Polymerase chain reaction (PCR) followed by length polymorphism restriction fragment analysis (RFLP) is useful for low-cost molecular diagnosis and screening. This cross-sectional study included 392 patients with congenital heart disease, described clinical features, and performed PCR-RFLP for analysis of polymorphism in three loci with a high heterozygosity rate located in the typically deleted region of 1.5 megabases. Heterozygosity excluded 22q11.2DS. Patients with homozygosity for the three markers underwent multiplex ligation-dependent probe amplification (MLPA) and fluorescence in situ hybridization (FISH) for the final diagnosis, estimating the prevalence of 22q11.2DS. The use of PCR-RFLP excluded 22q11.2DS in 81.6 % (n = 320) of 392 patients. Of the remaining 72 patients, 65 underwent MLPA, showing 22q11.2DS in five cases (prevalence, 1.27 %). Four of these five patients underwent FISH, confirming the MLPA results. All five patients with the deletion had heart diseases commonly found with 22q11.2DS (interrupted aortic arch, persistent truncus arteriosus, tetralogy of Fallot, and ventricular septal defect plus atrial septal defect). Two patients had congenital extracardiac anomaly (one with arched palate and micrognathia and one with hypertelorism). Three patients reported recurrent respiratory infections, and one patient reported hypocalcemia. All were underweight or short in stature for their age. This study contributed to showing the prevalence of 22q11.2DS in patients with any congenital heart disease, with or without other features of the syndrome. Patients with 22q11.2DS may not have all the major features of the syndrome, and those that are found may be due to the heart defect.

Screening newborn blood spots for 22q11.2 deletion syndrome using multiplex droplet digital PCR

BACKGROUND

The diagnosis of 22q11 deletion syndrome (22q11DS) is often delayed or missed due to the wide spectrum of clinical involvement ranging from mild to severe, often life-threatening conditions. A delayed diagnosis can lead to life-long health issues that could be ameliorated with early intervention and treatment. Owing to the high impact of 22q11DS on public health, propositions have been made to include 22q11DS in newborn screening panels; however, the method of choice for detecting 22q11DS, fluorescent in situ hybridization, requires specialized equipment and is cumbersome for most laboratories to implement as part of their routine screening. We sought to develop a new genetic screen for 22q11DS that is rapid, cost-effective, and easily used by laboratories currently performing newborn screening.

METHODS

We evaluated the accuracy of multiplex droplet digital PCR (ddPCR) in the detection of copy number of 22q11DS by screening samples from 26 patients with 22q11DS blindly intermixed with 1096 blood spot cards from the general population (total n = 1122).

RESULTS

Multiplex ddPCR correctly identified all 22q11DS samples and distinguished between 1.5- and 3-Mb deletions, suggesting the approach is sensitive and specific for the detection of 22q11DS.

CONCLUSIONS

These data demonstrate the utility of multiplex ddPCR for large-scale population-based studies that screen for 22q11DS. The use of samples from blood spot cards suggests that this approach has promise for newborn screening of 22q11DS, and potentially for other microdeletion syndromes, for which early detection can positively impact clinical outcome for those affected.

Síndrome de deleção 22q11.2 e cardiopatias congênitas

OBJETIVO: Revisar as características clínicas, etiológicas e diagnósticas da síndrome de deleção 22q11 e sua associação com as cardiopatias congênitas. FONTES DOS DADOS: Foram pesquisados artigos científicos presentes nos portais Medline, Lilacs e SciELO, utilizando-se descritores específicos como "22q11", "DiGeorge syndrome", "velocardiofacial syndrome", "congenital heart defects" e "cardio-vascular malformations". O período adotado para a revisão foi de 1980 a 2009. SÍNTESE DOS DADOS: As malformações cardíacas são os defeitos congênitos observados mais frequentemente ao nascimento e representam um problema importante de Saúde Pública. Dentre suas principais causas conhecidas destaca-se a síndrome de deleção 22q11, também chamada de síndrome de DiGeorge, síndrome velocardiofacial e CATCH22. Trata-se de uma doença autossômica domi-nante caracterizada por um fenótipo altamente variável, o que dificulta em muito seu reconhecimento clínico. Além disso, a maior parte dos pacientes apresenta uma microdeleção identificada principalmente por técnicas de citogenética molecular, como a hibridização in situ fluorescente, pouco disponíveis em nosso meio. De forma similar a outras síndromes, a síndrome de deleção 22q11 associa-se a certos defeitos cardíacos específicos, no caso os do tipo conotruncal. Apesar disso, não há ainda na literatura um consenso sobre quais os pacientes com car-diopatia congênita que deveriam ser investigados para a síndrome de deleção 22q11. CONCLUSÕES: Cardiologistas e cirurgiões cardíacos, espe-cialmente pediátricos, devem estar cientes das peculiaridades e dos cuidados dispensados à síndrome de deleção 22q11. Os indivíduos com a síndrome apresentam comumente alterações envolvendo vários sistemas, o que pode levar a dificuldades e a complicações durante seu manejo clínico e cirúrgico.

DiGeorge Syndrome: a not so rare disease

INTRODUCTION

The DiGeorge Syndrome was first described in 1968 as a primary immunodeficiency resulting from the abnormal development of the third and fourth pharyngeal pouches during embryonic life. It is characterized by hypocalcemia due to hypoparathyroidism, heart defects, and thymic hypoplasia or aplasia. Its incidence is 1:3000 live births and, despite its high frequency, little is known about its natural history and progression. ←This is probably due to diagnostic difficulties and the great variety of names used to describe it, such as velocardiofacial, Shprintzen, DiGeorge, and CATCH 22 Syndromes, as well as conotruncal facial anomaly. All represent the same genetic condition, chromosome 22q11.2 deletion, which might have several clinical expressions.

OBJECTIVES

To describe clinical and laboratorial data and phenotypic characteristics of patients with DiGeorge Syndrome.

METHODS

Patients underwent standard clinical and epidemiological protocol and tests to detect heart diseases, facial abnormalities, dimorphisms, neurological or behavioral disorders, recurrent infections and other comorbidities.

RESULTS

Of 14 patients (8m - 18y11m), only one did not have 22q11.2 deletion detected. The main findings were: conotruncal malformation (n = 12), facial abnormalities (n = 11), hypocalcemia (n = 5) and low lymphocyte count (n=2).

CONCLUSION

The authors pointed out the necessity of DGS suspicion in all patient presenting with heart defects, facial abnormalities (associated or not with hypocalcemia), and immunological disorders because although frequency of DGS is high, few patients with a confirmed diagnosis are followed up.

Síndrome de deleção 22q11.2: compreendendo o CATCH22

OBJETIVO:Realizar uma revisão dos aspectos históricos, epidemiológicos, clínicos, etiológicos e laboratoriais da síndrome de deleção 22q11.2, salientando-se a importância e as dificuldades do seu diagnóstico. FONTES DE DADOS: Pesquisa nas bases de dados Medline, Lilacs e SciELO, além da Internet e capítulos de livros em inglês, acerca de publicações feitas entre 1980 e 2008. Para isso, utilizaram-se os descritores "22q11", "DiGeorge", "Velocardiofacial" e "CATCH22". SÍNTESE DOS DADOS: A síndrome de deleção 22q11.2, também conhecida como síndrome de DiGeorge ou velocardiofacial, foi identificada no começo da década de 1990. A microdeleção 22q11.2 é considerada uma das síndromes de microdeleção genética mais frequentes em seres humanos. Caracteriza-se por um espectro fenotípico bastante amplo, com mais de 180 achados clínicos já descritos do ponto de vista físico e comportamental. Contudo, nenhum achado é patognomônico ou mesmo obrigatório. A maioria dos pacientes apresenta uma deleção pequena, detectada somente por técnicas de genética molecular, como a hibridização in situ fluorescente. Apresenta padrão de herança autossômico dominante, ou seja, indivíduos acometidos apresentam um risco de 50% de transmiti-la a seus filhos. CONCLUSÕES: Pacientes com a síndrome de deleção 22q11.2 frequentemente necessitam, ao longo de suas vidas, de um grande número de intervenções médicas e hospitalizações. O diagnóstico precoce é fundamental para a adequada avaliação e manejo clínico dos indivíduos e seus familiares.

Frequency of 22q11.2 microdeletion in sporadic non-syndromic tetralogy of Fallot cases

BACKGROUND

Tetralogy of Fallot (TOF) is a congenital conotruncal heart defect commonly found in DiGeorge (DGS) and velocardiofacial (VCFS) syndromes. The deletion of chromosome 22q11 has also been demonstrated in sporadic or familial cases of TOF. The aim of the present study was to investigate the frequency of del22q11 in patients with non-syndromic TOF seen at a tertiary Pediatric Cardiology care center.

METHOD

One hundred and twenty three non-syndromic TOF patients were selected and evaluated by history, physical examination and review of medical records. Venous blood was drawn for genomic DNA extraction after informed consent 22q11 microdeletion diagnosis was conducted through a standardized SNP genotyping assay and consecutive homozygosity mapping. Phenotype-genotype correlations regarding cardiac anatomy were conducted.

RESULTS

We evaluated 123 non-syndromic TOF patients for a 22q11 deletion. 105 (85.4%) patients presented pulmonary stenosis and 18 (14.6%) had pulmonary atresia. Eight patients (6.5%) were found to have a deletion. Of the deleted patients, three (37.5%) presented pulmonary atresia. We have verified a tendency towards a higher prevalence of pulmonary atresia when comparing TOF patients with and without 22q11 microdeletion.

CONCLUSIONS

22q11.2 deletion in non-syndromic TOF patients is present in approximately 6% of patients. We suggest a tendency towards a higher prevalence of pulmonary atresia in non-syndromic TOF patients with 22q11 microdeletion. Molecular genetic screening of non-syndromic TOF patient may be important for the correct care of these patients and a more specific genetic diagnostic and counseling.