Abstract

Multiple congenital anomalies may occur because of genetic and or environmental factors, as the aetiology. A retrospective study has been undertaken to report especially the genetic aetiology in 170 consecutively referred cases with multiple congenital anomalies (MCA). The information has been gathered from the duly filled proforma. Chromosomal analysis was carried out from the peripheral lymphocyte cultures.

One hundred seventy included 106 males, 63 females and the cord blood of a stillborn foetus with sex unidentified. Their age ranged from a stillborn foetus of 7 months to over 18 years. Consanguinity was noticed in 59; uncle - niece (22), first cousins (27) and distant relatives (10). Fourty two had a family history of multiple congenital anomalies. Twenty one were born prematurely.

Minor anomalies limited to the head or limbs varied from 0.6 to 55.9%. Major MCA varied from 4.1 to 89.4% with a maximal involvement of central nervous system.

Aetiology was determined in 102 (60%) and 68 (40%) were assumed to be multifactorial and or idiopathic. 29 (17%) had an eventful antenatal period with either maternal or foetal problems. Chromosomal abnormality accounted for 36.5% of the cases (62) and single gene disorders, sporadic syndromes and sequence for 6.5% (11).

Numerical chromosomal anomalies were observed in 55 (88.71%): Down syndrome (54) and a case of 47, XXX. Structural chromosomal abnormalities were seen in 7 (11.29%); translocation Down syndrome (46, XY, rob (14;21) (3), 46, XY, rob (21;21) (2); reciprocal translocation (46, XY, t(3;7)(q26;q33) (1)) and mosaic deletion in X (46, XX/46, XX, del (Xq)(q23q26) (1).

Autosomal dominant mode of inheritance was identified in 3 (Treacher Collins, Oculodentodigital, Stickler) and recessive in 5 (Cerebro Oculo Facial Skeletal, Peters Plus, Morquio one each respectively and Miller-Dieker in 2). Sporadic occurrence of Noonan/Brachyman - de - Lange syndromes and Pierre Robin sequence were observed.

Genetic counselling was given to the families specifically with reference to the risk of recurrence and management.

Introduction

The term congenital indicates that the anomalies are present at or from birth. Some of the anomalies are treatable (cleft lip and or palate); some are lethal (bilateral renal agenesis) and the third category is compatible with long-term survival but results in severe disability (brain defects). Developmental abnormality apparent at birth is seen in one in 40 newborns. A similar frequency has been suggested for the presence of subtle internal defect, which may become apparent at childhood or in adult life. The congenital

anomalies could occur as single (isolated) or as multiple anomalies. The anomalies are also grouped as major and minor. The major anomaly invariably has an adverse outcome on either the function or the social acceptability of the affected individuals and their families. In contrast, the minor anomaly is neither of medical nor of cosmetic importance; but in the presence of 2 or more minor anomalies then 10 to 20% risk exists to have a major anomaly.¹

The classification and nomenclature of the morphologic defects has grouped the anomalies clinically as malformation, disruption, deformation, dysplasia, sequence, syndrome and association. The first 4 are included under the isolated category and the last 3 are considered as the multiple categories.²

The aetiology for 50% is unknown and for the remaining 50%, environmental factors constitute 5 to 10% and the genetic factors 40%. Recent studies have shown that early embryonic genes may also be the most likely cause of the birth defects. Cascades of developmental genes act sequentially and involve complicated feedback loops, regulating the process of morphogenesis, have begun to be elucidated.³

A precise diagnosis, supported by appropriate laboratory investigations is important in the assessment of the aetiology as well as in providing the counselling. Finally, it goes a long way in the management, risk estimation and subsequent prevention of such anomalies.

With this view, the present study has been undertaken to analyze the aetiology of 170 consecutively referred cases with multiple congenital anomalies (MCA)

.Objectives

1. To report the general information on MCA (sex, age, birth order, consanguinity, parental age, family history, antenatal history, birth details, neonatal history).
2. To classify the MCA into major and minor defects.
3. To classify the MCA according to the diagnosis and aetiology (chromosomal/single gene disorders, syndromes, sequence/sporadic, multifactorial, environmental).

Material and Methods

One hundred and seventy consecutive cases of MCA associated with developmental or speech delay or an obvious mental retardation (MR), referred to the Division of Human Genetics over a period of 25 months, has been considered for the study.

A detailed proforma containing parental details, pedigree, family history, conception details, physical findings and the available investigations, was filled up. GTG banded lymphocyte cultures were analyzed for the karyotyping.

Results

I. General information

General information has been provided on sex ratio, age at referral, birth order, consanguinity, parental age, family history, antenatal history, birth details and neonatal history.

Sex ratio and Age at referral : There were 106 male and 63 female probands. It was noticed that MCA was more prevalent in males. The male to female sex ratio was 1.68:1. For the sample received from the cord blood, the sex was not known. 60.6% of the children have been referred in the preschool period i.e. below 3 years (n 103) and among them 70.8% were infants (n 73) (Table 1).

Birth order : Nearly, 46% (n 78) were noticed to be first-born (Table 2).

Consanguinity : Fifty nine patients (34.7%) were born to consanguineous parents. The different types of consanguinity noticed were uncle - niece (22), first cousins (27) and distant relatives (10).

Parental age : Parental age at conception was analyzed at 5-year intervals. Sixty one probands (35.9%) were born to mothers in the age group of 21 to 25 years. In the paternal age group of 26 to 30 years, 67 cases (39.4%) have been observed. This reflects the younger age group of the parents (Table 3).

Family history : Analysis of the family history of these patients revealed that 24.7% (n 42) had either a history of MR (15), similar problem as the probands (8), MCA (5), seizures (4), neural tube defects (3), developmental delay (2) and various other problems like a visual or hearing defect, minor skeletal anomalies of the limb (5). There were h/o spontaneous abortions as well in the parents.

Antenatal history : A problematic antenatal period during conception seen in 17% of the cases (n 29) was either due to maternal problems like pregnancy induced hypertension, diabetes mellitus, anaemia, thyroid problems or foetal problems like oligohydramnios, polyhydramnios, intra uterine growth retardation, abnormal foetal lie or reduced foetal presentations.

Birth details : A full term gestational period and a normal vaginal delivery was noticed in 98 cases (57.6%) whereas prematurity was seen in 21 cases (12.4%). 41 cases (24.1%) were delivered by Caesarean section, the indications for which were mainly non-progression of labour, failed trial labour or foetal distress. Low birth weight is taken as an index for failure to thrive, 3.5% (n 6) had birth weight < 1.5 kg. 48.8% of the patients (n 83) had a normal weight ranging between 2-3 kg. Birth asphyxia could have been the probable cause of MR in 12 patients (7.1%) who did not ‘cry’ at birth.

Neonatal problems : Nearly 50% of the patients had manifested one or the other of the neonatal problems like failure to thrive, feeding problems, incubator care, respiratory distress, recurrent infections, seizures and prolonged physiologic jaundice.

II. Classification - MCA into minor and major anomalies

Minor anomaly : Most of the minor anomalies were found pertaining to the head or limbs. Commonest ones noticed were hypertelorism, low set ears, mongolid slant of eyes, epicanthic folds, clinodactyly of little finger. It was noticed that most of the Down syndrome (DS) patients had all these features (Table 4).

Major anomalies : It was seen that central nervous system was the maximally involved one with 89.4% patients (n 152) showing its involvement in one way or the other like delay in developmental milestones or speech, microcephaly, seizures, behavioural problems, or altered muscle tone. Involvement of musculo-skeletal system was noticed in the form of spinal, chest wall or limb deformities. Cardiovascular involvement has manifested as murmurs, ventricular septal defect, aortic stenosis patent ductus arteriosus and mitral valve prolapse. Urogenital involvement was seen as micropenis, small scrotum or cryptorchidism (Table 5).

III. Classification - MCA as per aetiology

Aetiology was determined in 102/170 cases (60%). The remaining 68 (40%) were assumed to be multifactorial and or idiopathic. 29/170 probands (17%) had an eventful antenatal period with either maternal or foetal problems. Chromosomal abnormality accounted for 36.5% of the cases (62/170) and single gene disorders, sporadic syndromes and sequence for 6.5% (11/170) (Table 6).

Numerical abnormalities of chromosomes (55/62, 88.71%) mainly comprised Down syndrome (54) (Trisomy 21 (51), Mosaicism (3)) and a case of 47, XXX. Structural abnormalities were seen in 7 (11.29%) and they were : translocation Down syndrome 5 (46, XY, rob (14:21)(3), 46, XY, rob (21:21)(2); reciprocal translocation between 3 and 7 (46,XY, t(3;7)(q26;q33)(1) and mosaic deletion in X (46,XX/46,XY, del (Xq)(q23;q26).

Single gene disorders were autosomal dominant mode of inheritance in three (Treacher Collins, Oculodentodigital, Stickler) and autosomal recessive in five (Cerebro Oculo Facial Skeletal (COFS), Peters Plus, Morquio one each respectively and Miller - Dieker in two). Noonan syndrome, Brachyman-de-Lange syndrome and Pierre Robin sequence were detected to be sporadic (Table 7).

Discussion

The present work has been discussed as per the observations.

I. General information

Sex ratio and Age at referral (Table 1)

In general, a higher sex ratio of males (3:2) having MCA has been reported except in Trisomy 13 and mosaic cases of Down syndrome.4,5 The differences in the sex ratio may be attributed to the intra-uterine selection or the preferential segregation of Y with 21. In the present study also a higher ratio of male patients as well as a high occurrence of trisomy 21 have been observed.

The higher prevalence of birth defects in the pre-school children reflect the parental awareness about early detection/diagnosis/intervention, thereby hoping for a better prognosis.

Birth order (Table 2)

The higher percentage of the first-born reflected a younger parental age and the probability of these parents having adopted preventive measures or prenatal diagnosis, in the event of their having had a child with birth defects.

Consanguinity

There is conflicting opinion about the influence of consanguinity on MCA.6-12 In India, the reported incidence of consanguinity is between 5 and 60% and the commonest type of consanguineous relationship is that between uncle and niece.3,7 Many studies have shown that among the offspring of consanguineous marriages there is an increased incidence of both birth anomalies as well as defects which may set in later, such as hearing loss or mental retardation. The association of consanguinity to MCA has been attributed to homozygosity for the mutant genes, whereby the mating in consanguinity gives exactly the conditions most likely to enable a rare feature to show itself. The present study findings regarding consanguinity and associated birth defects in 34.7% cases were more or less similar to the views expressed in literature. The higher value of the first cousin relationship is similar to the observations in an Arab study of 25 to 54%.³

Parental age (Table 3)

In India, the marriageable age group for couples is relatively early and they tend to complete their family life also at an earlier age. Moreover, in consanguineous union, younger age at marriage seemed to be prevalent.13 Probably the same points also accounted for the younger parental age noticed in the present study.

Antenatal/family history; birth details; neonatal problems

The h/o spontaneous abortions obtained in the family history might probably be due to birth defects of a severe degree in the conceptus, which was not compatible to life. Reviewing the family history throws light on the type of malformation and its aetiology. When a h/o another sibling having the same feature as the proband is obtained, it gives a clue that the patient may have an autosomal recessive condition even when consanguinity is not observed in the parents. This knowledge is important while giving the risk figures for counselling. The various neonatal and medial problems encountered by the patients may be because of the functional deficit associated with the malformations. For instance, it is a known fact that Down syndrome patients are more susceptible to infections as they have a low immune mechanism.

II. Classification: minor and major birth defects

Minor anomalies (Table 4)

Congenital anomalies could be single or multiple; and of major or minor clinical significance. Single minor anomalies are seen in about 14% of newborns.2 Usually, they are of no serious medical significance, but indicate the presence of an associated major anomaly. It has been noticed that 90% of the infants with 3 or more minor anomalies manifest one or more major defects. The incidence of multiple major anomalies in embryos is around 10 to 15% and most of them are spontaneously aborted.14

Minor anomalies are more or less to be treated as clues to more serious problems as well as towards the recognition of syndromes because they are neither of medical nor cosmetic significance. Minor anomalies are found to occur in 10% of the newborns. If 2 or more minor anomalies have been noticed, then there is a 20% risk of the baby having a major malformation.3 Minor anomalies may also bee seen as a familial trait. The developmental origin of minor anomalies is due to altered mechanical forces affecting the development of an otherwise normal tissue. It might also occur as a result of a primary malformation. In the present study, the frequency of the minor anomalies ranged from 0.6% to 55.9%. The differences noticed are due to the overlap of many features manifested in the patients.

Major multi-systemic anomalies definitely have an adverse outcome on either the function or social acceptability of the individual. Surveys have observed that 2-3% have at least one major anomaly. In some instances, major anomalies like mental deficit, deafness seemed to manifest later in life in which case the incidence becomes 5%. In the present study, the major systems involved were central nervous system, Cardio Vascular system, Digestive system, Uro-genital and Musculo - Skeletal system.¹⁵

III. Classification - MCA as per aetiology (Tables 6 and 7)

The incidence of congenital anomalies is between 6 and 20%.¹⁴ The causes of these anomalies are grouped into genetic (40%) [single gene disorders (7%), chromosomal disorders (8%), multifactorial (25%)]; and environmental factors (10%). The causes are not known for nearly 50% of the congenital anomalies i.e. idiopathic.¹⁴

Genetic factors are the most important causes of congenital anomalies accounting for one third of all birth defects and 85% of anomalies with a known cause (Carlson 2004, Rimoin et al 2007).^16,17

Chromosomal abnormality (CA) (Tables 6 and 7)

Chromosomal abnormality, either numerical or structural, may involve the autosomes and or the sex chromosomes and the manifestations are due to a genetic imbalance. These chromosomal abnormalities lead to dosage effects of the individual genes or a general developmental instability caused by a number of abnormal gene products. These changes may initiate anomalies by biochemical or other means at the subcellular, cellular or tissue level.¹

The reported frequency of chromosomal abnormality in MCA is between 16.6%18 and 22.6%.¹⁹ In the present study, the breakdown of the numerical and the structural chromosomal abnormality seemed to be similar to that quoted in literature, with Down syndrome being the commonest anomaly. The observed higher percentage of chromosomal abnormality may be because of the inclusion of the polymorphic variants also.

Single gene disorders (Table 6)

Gene defects account for 7% to 8% of congenital anomalies. A mutation usually involves a loss or change in the function of the gene and is a permanent, heritable change in the DNA sequence. Rarely does a mutation lead to developmental improvement; most mutations are deleterious and some are lethal.20 Anomalies resulting from gene mutations are inherited according to Mendelian laws and hence it is possible to give the risk of recurrence in the probands or their close relatives. The types of single gene defects are as per the location of the genes in the autosomes or sex chromosomes, as well as based on the expression of the single or double copy of the mutated genes known as dominant or recessive respectively.

In the present study, autosomal dominant (AD) mode of inheritance has been noticed in three cases viz: Treacher Collins syndrome, Oculo Dento Digital syndrome, Stickler syndrome; autosomal recessive (AR) inheritance in five cases viz. COFS syndrome, Peters Plus syndrome and Morquio syndrome one each respectively and Miller Dieker syndrome in two; and Brachman-de Lange syndrome and Noonan syndrome diagnosed to be sporadic. One case of Robin sequence was also observed.

A syndrome is a pattern of multiple anomalies derived from a single known structural defect or mechanical factor. The initiating factor may be a chromosomal anomaly or a single gene defect. A sequence in the other hand reflects the phenotypic manifestations occurring as a consequence of a cascade of events initiated by a single primary factor. Microdeletions, as the name implies, are due to sub microscopic deletions where the loss involves only a few genes at closely adjacent loci.

In Pierre-Robin syndrome or Robin sequence noticed in a female proband, the primary initiating defect could have been hypoplasia of the mandibular area prior to 9 weeks in utero which then would have lead to a chain of associated anomalies as seen in the patient.

Multifactorial inheritance (Table 6)

Multifactorial inheritance conditions very often are single major anomalies or they may also be seen as part of the phenotypes in syndromes developing due to various causes. This is the commonest cause of congenital anomalies, wherein the emphasis is on genetic and environment i.e. nature versus nurture. As genetic factor, it is due to the polygenic effects crossing the liability threshold for a particular condition. In this study, cases of cleft lip/palate and some cases of MR could be considered as multifactorial conditions.

Environmental (Table 6)^16,17

Environmental factors cause 7 to 10% of congenital abnormalities. Certain teratogens may cause developmental disruptions following maternal exposure to them. Included in this category are radiation, chemicals, drugs and infections. The organs and parts of the embryo are most sensitive to teratogenic agents during periods of rapid differentiation. Because, biochemical differentiation precedes morphological differentiation; the period during which the structures are sensitive to interference by teratogen precedes their stage of visible development by a few days. Some environmental influences adversely affect embryonic development by a few days. Some environmental influences adversely affect embryonic development by altering intra cellular compartment, cell surface, extracellular matrix, and foetal environment.13 In the present study, a clear cut environmental factor could not be attributed, except for the presence of foetal rubella syndrome in one case and in 2 mothers who gave the history of having undertaken hormonal treatment prior to conceivement. In the present study, the aetiology could be identified in 50% cases and in the remaining 50%, it is idiopathic, consistent with that reported in literature. In general, the discrepancy seen may be because of the sample size, sample bias and clinical evaluation. Lack of full details in some cases may be another contributing factor.

Management and Genetic Counselling (GC)²¹

Keeping in mind, the diagnosis and the aetiology, appropriate counselling is being provided to the patients and their families. GC procedure includes explanation of the cause of the defect, the outcome, the management, the risk of recurrence, the available prenatal diagnosis and the reproductive options, over various sessions.

A more specific counselling could be given to cases with chromosomal abnormality and single gene disorders. Depending on the type of chromosomal anomaly, the age and karyotype of the parents, recurrence risk varies. In a unique case of the patient showing t(3;7) and where the parents had a normal karyotype, the defect was considered to have arisen de-novo and hence the risk of occurrence in subsequent pregnancies was negligible. For those cases diagnosed to have autosomal dominant or autosomal recessive pattern of inheritance, the risk of recurrence is either 50% or 25% respectively for each conception. For multifactorial inheritance, only empirical risk factors based on the frequency of the anomaly in the general population could be given. For the cases of microdeletion and Robin sequence, the recurrence risk was given as < 1%.

Family studies including parental studies were undertaken in relevant cases to determine the parental origin of the chromosomal defect followed by appropriate counselling.

Conclusion

Congenital anomalies may be induced by genetic or environmental factors that cause derangements during prenatal development. Most common birth defects show multifactorial inheritance with a threshold liability and are determined by a combination of genetic or environmental factors.

Analysis of the birth defects and aetiology revealed that genetic aetiology accounted for 43% (73) (chromosomal abnormality 36.5% (62), single gene disorders 6.5% (11)) and environmental 17% (29). The rest of the cases (40%) were assumed to be multifactorial and or idiopathic.

The study was added information to the contribution of the genetic aetiology to the cause of MCA. A knowledge of the aetiology plays a pivotal role in approaching the cases, aids in the development of a specific treatment plan, helps the families to understand the prognosis and recurrence risk and helps on a community level to develop preventive strategies. The causal relationship between the MCA and chromosomal defects is fairly well established.

Acknowledgement

Patients and their families are gratefully thanked for their co-operation and consent.

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