NEONATAL SURGERY - 1976

2. SPECIAL SECTIONS

7. Genetically Determined Diseases and Malformations

   The Study of hereditary malformations is based on advances in molecular biology, Cytology, medical genetics, clinical biochemistry, and related fields. A major contribution to The Development of medical and clinical genetics in our country was made by N. P. Dubinin, V. D. Timakov, N. I. Zhukov-Verezhnikov, N. P. Bochkov, E. F. Davidenkova, A. A. Prokofieva-Belgovskaya, B. V. Konyukhov, and others.

Under METABOLISM/18.html">The Influence of adverse genetic factors, any Organs and Tissues of a newborn infant may undergo abnormal development. In some cases, a congenital defect affects only a single organ, while in others it constitutes an integral part of a complex clinical syndrome that includes Anomalies of the extremities, eyes, facial Skeleton, and Internal Organs. The development of such multiple malformations is frequently combined with Metabolic Disorders, as well as neurohumoral and neuroendocrine dysfunctions.

Biological approaches to Structure/149.html">The problem of Congenital Malformations are based on specific Levels of Organization of hereditary structures. Currently, three such levels are generally distinguished: 1) the Gene (molecular) level; 2) the chromosomal hereditary apparatus (chromosomal level); and 3) the system comprising the full Complement of Chromosomes (genomic level). Mutations occurring at any of these three levels serve as the underlying cause of Hereditary diseases and Congenital Malformations.

The clinical picture of hereditary anomalies is frequently indistinguishable from anomalies of exogenous origin (the phenocopy problem). This can be attributed to the fact that in both cases, Embryogenesis involves alterations in the exact same PHYSIOLOGICAL AND BIOCHEMICAL processes—in the first instance under the influence of genetically deficient enzyme systems, and In the second under the IMPACT OF ENVIRONMENTAL factors. Fetal anomalies during intrauterine development are intimately linked to the mother's physiological state. Clinical observations indicate that the incidence of congenital anomalies increases with maternal age. The potential for Embryonic and Fetal damage is particularly high during the so-called Critical periods of development, i.e., those moments in embryogenesis when the differentiation of specific structures proceeds with maximum intensity.

All congenital malformations associated with genetic factors can be provisionally divided into three groups: 1) those caused by Gene Mutations; 2) those caused by chromosomal mutations; and 3) those partially caused by genetic factors.

Malformations Caused by Gene Mutations

   The hereditary nature of a disease implies, first of all, its familial distribution. However, the majority of malformations occur not as familial cases, but as sporadic (isolated) ones. Therefore, the division of hereditary anomalies into familial and sporadic is purely conventional, and contrasting them during clinical and genetic evaluation is unjustified.

The General characteristics of the clinical manifestations of a hereditary defect depend on the action of one or more pathological (mutant) genes. In this regard, The Effect of a pathological gene can be characterized by its penetrance (frequency of manifestation) and expressivity (degree of Development of the trait it controls).

Clinical and genetic analysis requires a thorough examination of not only typical cases, but also atypical, abortive, and forme fruste presentations of a given anomaly. In view of the clinical polymorphism so characteristic of hereditary diseases, the identification of both typical symptoms and microsymptoms of the condition is of paramount importance.

Hereditary forms of diseases are characterized by a specific mode of inheritance. Chung et al. (1960) proposed criteria for determining the main inheritance patterns: autosomal dominant, autosomal recessive, and X-linked (sex-linked).

Autosomal dominant inheritance with complete penetrance is characterized by the following features: 1) direct transmission from generation to generation "without skipping" generations; 2) every affected child has an affected parent; 3) in a marriage between an affected heterozygote and a healthy partner, the expected frequency of affected children is 50%; 4) both sexes are affected to an equal degree; 5) "dominant" genes are known exclusively by their Clinical presentation in heterozygotes, whereas homozygotes are exceedingly rare.

If carriers of the pathological dominant gene are clinically healthy (so-called incomplete penetrance), the disease "skips" one or more generations, and the frequency of affected children decreases. In patients with a mild (abortive) form of the disease, a Diagnosis can be established only after a comprehensive clinical, genetic, and laboratory evaluation (Fig. 28).

Class="center">Fig. 28. Autosomal dominant inheritance of multiple cartilaginous exostoses across three generations (author's observation).

With a dominant inheritance pattern, it is extremely rare to observe a marriage between two individuals suffering from the same disease. An affected person is almost always a heterozygote—that is, a carrier of both normal and abnormal genes—whereas clinically healthy individuals in such families are sound not only clinically, but genetically as well. A burdened family history in such instances is transmitted via either the maternal or the paternal line, meaning it is "unilateral" in nature. The theoretical risk of disease for each child can be determined even prior to the first Pregnancy. If one parent is affected, the probability of the first and each subsequent child being affected is 50%. A healthy child does not carry the pathological trait.

The most typical Examples of dominant inheritance include Syndactyly, polydactyly, polyphalangy, Macrodactyly, and brachydactyly. It is clinically unwarranted to attempt to eliminate these malformations through selective breeding, as they do not pose a threat to life. The aforementioned anomalies frequently form part of complex clinical syndromes (e.g., Marfan Syndrome).

Another example of a systemic disease caused by degenerative Skin changes is Ehlers-Danlos syndrome, which exhibits an autosomal dominant or X-linked inheritance pattern. Among the malformations that may warrant a surgeon's attention, diaphragmatic hernia, ectasia of PARTS OF THE digestive and respiratory tracts, and dissecting aortic aneurysms should be noted.

Malformations inherited in an autosomal dominant manner include coarctation of the aorta, atrial septal defect, patent ductus arteriosus, Arthrogryposis (multiple congenital contractures syndrome), Turner-Kieser syndrome (patellar hypoplasia, knee dislocation, etc.), Nievergelt syndrome associated with upper and lower limb malformations, neurofibromatosis (Recklinghausen's disease), gastrointestinal polyposis, retinoblastoma, congenital lymphedema, tuberous sclerosis (Bourneville's disease), various dysostoses (cleidocranial, maxillofacial, craniofacial), Osteogenesis Imperfecta, hereditary ptosis, ectopia lentis, and others.

In addition to dominant inheritance determined by a single gene pair (monogenic inheritance), di- and polygenic transmission, as well as sex-linked and sex-limited transmission, are also possible.

Autosomal Recessive Inheritance with complete penetrance is characterized by the following features: 1) parents and relatives, aside from siblings, are usually unaffected; 2) if recessive pathological genes are allelic—that is, located at identical loci on homologous chromosomes—all children born to two affected parents will be affected; 3) from a marriage between two clinically healthy heterozygotes, 25% of the children will be affected and 50% will be healthy carriers, similar to their parents; 4) both sexes are affected to an equal degree; 5) if the disease is rare, The Significance of consanguinity among the parents increases.

Incomplete penetrance in autosomal recessive inheritance presents a major challenge in genetic analysis, because these families may yield a higher number of affected individuals than predicted by theoretical calculations (Fig. 29).

Fig. 29. Autosomal recessive inheritance in congenital myopathy.

   Although recessive disorders predominantly include various enzymopathies (so-called metabolic blocks), congenital malformations also frequently exhibit a recessive pattern of inheritance. These include acrocephalosyndactyly (Apert syndrome), acheiropodia (absence of hands and feet), recessive forms of arthrogryposis, chondroectodermal Dysplasia (Ellis-van Creveld syndrome), intellectual disability and retinitis pigmentosa combined with hypogonadism, obesity, and polydactyly (Laurence-Moon-Biedl syndrome), concomitant congenital strabismus, gargoylism (Mucopolysaccharidoses), certain forms of intestinal polyps that may subsequently undergo malignant transformation, and others.

In addition, There is a broad group of congenital malformations that can only be conditionally classified under a recessive pattern of inheritance, as they are predominantly observed as sporadic forms. These include the absence of various Muscle groups (such as those of the neck and chest), Clubhand, atresia of the Esophagus and various sections of the intestine, pancreatic anomalies (annular, cystic fibrosis), embryonic and diaphragmatic hernias, spinal hernias, and bladder exstrophy. Since the inheritance pattern in these cases has not been definitively established, we can only tentatively consider them as recessive.

Recessive hereditary malformations are clinically manifested when both parents happen to be carriers of the recessive gene (so-called heterozygotes). According to theoretical calculations, the probability of the disease occurring is 25% (homozygous for the recessive pathological gene), the chance of bearing a heterozygous child is 50%, and that of a healthy child (homozygous for the normal gene) is 25%. A marriage between an affected individual and a healthy one will yield 100% heterozygotes in the offspring. A marriage between an affected individual and a heterozygote will produce 50% affected offspring and 50% heterozygotes (carriers). The identification of heterozygotes is of particular significance in cases of consanguineous marriages within families that carry a given recessive anomaly. Clinical evidence of heterozygosity may include "minor" phenotypic signs of the condition. However, neither clinical nor clinical-laboratory Methods are frequently able to reliably identify hidden carriers of the pathological gene, which severely complicates drawing Conclusions regarding the hereditary Nature of the anomaly. It should be kept in mind that, aside from simple autosomal monohybrid recessive inheritance governed by a single pair of recessive traits, other forms exist: polygenic recessive inheritance; sex-linked recessive inheritance; and sex-limited recessive inheritance.

In X-chromosome-linked inheritance (Sex-Linked Inheritance), the following features are observed: 1) parents and relatives, with the exception of maternal male relatives, are typically healthy; 2) homozygous affected males do not transmit the disorder to their children, but all of their daughters are heterozygous carriers; 3) heterozygous female carriers are clinically healthy but transmit the condition to 50% of their sons, while 50% of their daughters are heterozygotes, just like their mothers; 4) affected females are born exclusively from marriages between female carriers and affected males; 5) every affected male is born to a carrier female. Furthermore, the occurrence of new mutations is also possible.

When a pathological gene is localized on the X chromosome, depending on whether it is dominant or recessive, one distinguishes between dominant sex-linked inheritance and recessive sex-linked inheritance (Fig. 30). Sex-linked inheritance should be distinguished from sex-limited inheritance. A classic example of a fully sex-limited dominant trait is hypospadias.

Fig. 30. Sex-linked inheritance of congenital limb anomalies.

Developmental Malformations Caused by Chromosomal Mutations

According to WHO data (1965), the genetic risk of having a child with a severe malformation or developmental anomaly is at least 2.5%. Subsequent extensive research demonstrated that severe congenital anomalies affect approximately 5% of newborns (Jacobs et al., 1970, et al.). Congenital anomalies are associated with karyotype aberrations in 70.2% of newborns, with more than half of these considered individuals with normal trait variations. A significant number of somatic congenital defects are linked to numerical or structural chromosomal changes (aberrations). In the population, Klinefelter syndrome occurs with a frequency of 0.25%, Down syndrome at 0.2%, Triple X syndrome at 0.125%, Turner syndrome at 0.04%, Edwards syndrome at 0.02%, and Patau syndrome at 0.007%. Among the 22 pairs of autosomes and the pair of sex chromosomes that make up the Human Karyotype, aberrations of the 13th, 18th, 21st, and sex chromosomes X and Y are the most frequent.

Developmental disorders resulting from Chromosomal aberrations can be divided into two categories: somatic malformations and anomalies of sexual development. Most DISORDERS OF SEXUAL development are associated with numerical or structural aberrations of the sex chromosomes. However, with autosomal aberrations, defects in The formation of the genital organs are not uncommon, and with sex chromosome aberrations, somatic defects are the rule rather than the exception.

In autosomal aberrations, the majority of symptoms are not specific to any particular syndrome. For instance, syndactyly is observed in Down syndrome and trisomy 18; abnormally shaped, low-set auricles occur in cri-du-chat syndrome, trisomies 13 and 18, 18q- syndrome (deletion¹ of the long arm of the 18th chromosome), and 18p- syndrome (deletion of the short arm of the 18th chromosome). Congenital cleft lip is encountered in trisomies 13 and 18, epicanthus (fusion of the upper and lower eyelids) in trisomies 18 and 21 as well as in 18q- and 18p- syndromes. Hyperteleorism (an increased distance between the eyes) is present in cri-du-chat syndrome and 18p- and 18q- syndromes, whereas hernias are characteristic of Patau and Edwards syndromes.

¹ Deletion: a structural alteration of a chromosome associated with the loss of a portion of it.

Malformations of the Musculoskeletal and Connective Tissue Systems. In the presence of an extra 18th chromosome (trisomy 18), the patient's appearance is quite characteristic. The Skull is elongated, with a wide, prominent occiput, a narrow forehead, an underdeveloped lower jaw, congenital cleft lip, low-set abnormally shaped auricles, a small triangular Mouth, and ptosis. The chest appears compressed vertically: barrel-shaped, short, with a broad Sternum. The pelvis is typically narrow, the thighs are approximated, and the mobility of the hip joints is severely restricted. FOOT anomalies (talipes equinovarus) and hand anomalies are typical: the palm is broad with short fingers and a specific positioning of the second and fifth fingers due to hypoplasia of the thenar and hypothenar Muscles. In some cases, patients exhibit syndactyly, nail anomalies, inguinal and umbilical hernias, and corneal opacity.

Patients with trisomy 21 are characterized by a small, round skull with a flattened occiput; they present with an underdeveloped Maxilla, a round face with a short, broad Nose, a depressed nasal bridge, closely set slanting eyes (slanted downward and inward from the outside), and abnormal auricles. The mouth is frequently half-open, Teeth are abnormally shaped and carious, and the Tongue is thick with transverse furrows. Stature is usually short, limbs are shortened, and increased joint mobility is often observed due to muscular hypotonia, ligamentous laxity, or shallow acetabulae; hernias, syndactyly between the second and third toes, an increased gap between the First and Second toes, curved and shortened fifth fingers, and a single transverse palmar crease may also be present.

Trisomy 13 is marked by a brachycephalic skull structure, microcephaly, congenital cleft lip and palate, microphthalmia or anophthalmia, malformed low-set ears, an underdeveloped lower jaw, and corneal opacity. Malformations of the feet, increased flexibility of the thumbs, ulnar polydactyly and syndactyly, hernias, and coloboma are frequently noted.

Cri-du-chat syndrome is caused by the absence of a portion of the short arm of chromosome 5, manifesting as a deletion of half of the short arm, the presence of a ring chromosome, or a balanced translocation between the 5th chromosome and another chromosome. Due to abnormal laryngeal structure, the voice pitch resembles a cat's meow, a symptom that gave the syndrome its name. Common symptoms include microcephaly, a round face with closely set slanting eyes, epicanthus, low-set abnormally shaped auricles, micro- and retrognathia, muscular hypotonia, and limb paresis.

Somatic anomalies of 18q deletion syndrome manifest as microcephaly, facial disproportion (hypoplasia of the midface, abnormally low-set ears with a prominently protruding antitragus, Middle ear anomalies), hypertelorism, epicanthus, and muscular hypotonia.

Malformations of the Internal Organs and Central Nervous system. In 18q- syndrome (deletion of the long arm of chromosome 18), renal and cardiac malformations are observed. Down syndrome features endocrine gland dysfunctions accompanied by corresponding changes. Brain abnormalities include hypoplasia of the Cerebellum and Brainstem, ventricular Hydrocephalus, and various morphological anomalies of Neurons. Cardiac defects include patent ductus arteriosus, ventricular or atrial septal defects, coarctation of the aorta, and Tetralogy of Fallot. In trisomy 18, a small Placenta and a single umbilical artery can be detected at birth. Renal malformations typically present as a duplex Ureter or Hydronephrosis, while cardiac defects manifest as patent ductus arteriosus or ventricular septal defect. Brain pathology includes demyelination of the Projection Pathways in the cerebral hemispheres and cerebellum. In trisomy 13, malformations of the Kidneys, Heart, and brain are recorded, along with facial hemangiomas. The most frequently identified cardiac defects are patent ductus arteriosus and ventricular septal defect. Brain anomalies manifest as a reduction in the number of gyri, displacement of brain structures, and anencephaly.

Somatic anomalies in sex chromosome aberrations are most pronounced in X monosomy (Turner syndrome). Patients with complete or partial monosomy are characterized by short stature and a shortened neck with a low posterior hairline. Malformations are observed in the urinary, cardiovascular, osteoarticular, musculoskeletal, and connective tissue systems. A shift and disproportion between the neurocranium and viscerocranium are frequently observed. Multiple skeletal anomalies, delayed ossification, failure of epiphyseal-metaphyseal fusion, Osteoporosis, early eruption and deformation of teeth due to idiopathic ROOT resorption, underdevelopment of the lower jaw (micrognathia or retrognathia), and malocclusion are characteristic. Spinal deformities (Kyphosis, Scoliosis, Spina bifida, vertebral fusion, rib fusion, vertebral body shortening) are common. Limb abnormalities frequently include wrist joint deformities, pes valgus, valgus deviation of the elbow and knee joints, and syndactyly. Shortening of the four metacarpal and Metatarsal Bones leads to shortened fingers and toes; shortening and curvature of other digits and syndactyly are occasionally observed. Muscular System findings include the absence or hypoplasia of individual extraocular muscles, which likely accounts for strabismus and astigmatism. Absence of the levator palpebrae superioris muscle leads to ptosis. Noteworthy features include laxity of the joint ligamentous apparatus, nail dystrophy, morphologically abnormal auricles, and lateral webbing of the neck (pterygium colli). Turner syndrome frequently reveals coarctation of the aorta, transposition of the great vessels, patent ductus arteriosus, and stenosis of the aortic or pulmonary trunk. Renal anomalies are also common, presenting as dysplasia of one Kidney, a Horseshoe kidney anomaly, or duplication of the Ureters or renal pelves.

Malformations of internal organs in polisomies are significantly less severe and less frequent than in monosomies. The phenotype of patients with an XYY genotype is characterized by tall stature and macrognathia, while anomalies may be completely absent altogether.

In Klinefelter syndrome with an XXY genotype, developmental anomalies become apparent at various ages, starting from the neonatal period. As the number of extra chromosomes increases, the frequency of abnormalities rises: valgus deviation, joint hypermobility, and radioulnar synostosis are encountered. Affected individuals typically present with tall stature, elongated limbs, a eunuchoid habitus, and a predisposition to obesity.

When the number of both sex chromosomes, X and Y, increases (polysomy), features of acromegalism and cardiovascular anomalies are typically observed.

The mechanism responsible for numerical chromosomal aberrations such as monosomies, trisomies, and polysomies is considered to be nondisjunction, although the Etiology and underlying pathways leading to nondisjunction remain insufficiently studied. It is reasonable to assume, however, that even in these cases, critical cellular mechanisms governing the spatial Structural organization of Cell Nucleus chromosomes play a decisive role. As a result of nondisjunction During the first and second meiotic divisions, the following types of Gametes may arise: X, Y, O, XY, XX, XY, XXY, XYY, XXYY, X, O, XX, XXX, XXXX. Zygotes carrying YY, YO, or OO sex chromosome complements are lethal, whereas the majority of chromosomal anomalies resulting from the fusion of normal and abnormal zygotes have been identified and investigated.

The presence of two or more genotypically distinct chromosomal cell lines (clones) in patients is termed mosaicism. The percentage ratio of these clones, barring any subsequent selective advantage of one over the other, will depend on the developmental stage at which nondisjunction occurred. The clinical picture depends on the predominance of a given cell clone in the respective tissue or organ and on the interaction of functioning genes within Cells possessing an abnormal chromosomal complement. In various structural alterations of one of the X chromosomes associated with partial monosomy, the Clinical presentation of Turner syndrome is somewhat attenuated. Distinct clinical boundaries between the Various Forms of the syndrome do not exist. Karyotypic Variants of the so-called mixed gonadal dysgenesis group, resulting from karyotypic mosaicism, are highly diverse—for example, 45,X/46,XX; 45,X/46,XXp; 45,X/46,XXqi; 45,X/46,XY; 45,XO/46,XX/46,XY, etc. The presence of the 46,XX cell clone dictates the development of ovarian tissue and, consequently, the potential for ovulation, menstruation, and childbearing. Cell clones of 46,XY or a clone with a deleted Y chromosome determine the presence of testicular tissue, which leads to virilization, a male body habitus, enlargement of the Clitoris, or even the development of a nearly normal-sized Penis.

Somatic anomalies are less common. Sometimes this clinical variant is referred to as mixed gonadal dysgenesis. Gonadal dysgenesis with a 46, XY karyotype is quite rare, meaning the karyotype and phenotype do not match.

In this form, secondary sexual characteristics are usually absent, somatic anomalies are lacking, and both internal and external genitalia are underdeveloped. Individuals with male pseudohermaphroditism have a 46, XY karyotype, and very rarely 45, Х/46, XYq —; 45, Х/47, XXq — у; 45, ХО/46, XY, etc. All patients

can be divided into two subgroups: 1) individuals with ambiguous or predominantly male external genitalia; 2) individuals with female external genitalia and developed breasts. In true Hermaphroditism, about 60% of hermaphrodites had a 46, XX karyotype, and 40% had a normal or deleted Y-chromosome in their karyotype. However, The Role of chromosomes in these cases remains insufficiently clear due to the inability to rule out cryptic mosaicism or the translocation of a Y-chromosome fragment to one of the autosomes.

In the vast majority of cases of seminiferous tubule dysgenesis, clinicians deal with Klinefelter syndrome, caused by X-chromosome polysomy.

Congenital anomalies of sexual development occur not only with sex chromosome aberrations, but also with numerical and structural Autosomal anomalies. For instance, cryptorchidism is observed in trisomy 13 and 18 syndromes, while genital hypoplasia occurs in trisomy 21 syndrome (their underdevelopment is apparently associated with gonadal dysfunction, usually observed in preschoolers). After 12 years of age, the genitalia in boys may reach normal sizes.

Malformations partially caused by genetic factors

This group includes Congenital heart defects, pyloric stenosis, cleft lip and palate, anencephaly and spina bifida, congenital hip dislocation, and Clubfoot. The probability of these defects is determined exclusively on an empirical basis. "Empirical risk" means the probability of a given defect occurring based on practice and observation rather than theoretical calculations. In newborns, these malformations are observed with a frequency of 1 to 3 per 1000.

The Selection/32.html">Genetic heterogeneity of these defects is manifested by the fact that they occur more frequently in some families and less frequently in others. The Importance of genetic factors in their origin is indicated by a higher prevalence of the defect among affected relatives compared to the general population, variable frequency across both sexes, and a relatively high degree of concordance between monozygotic twins.

Pyloric stenosis is a relatively common condition in the early months of life. A correlation has been established between the incidence of the disease and consanguinity, as well as a higher concordance rate in monozygotic twins compared to dizygotic ones. Specifically, the risk for the second twin if the first is affected is 67% in monozygotic twins, whereas it is only 3% in dizygotic twins. The most compelling data come from the analysis of familial cases. The morbidity is highest among male relatives of affected female patients and lowest among relatives of affected male patients.

Congenital cleft lip, palate, and alveolar ridge are sometimes viewed from an embryological perspective as varying degrees of the same defect. Clinical and genetic analysis reveals that relatives of a proband with a cleft lip, or a combination of cleft lip and palate, frequently present with cleft lip and palate, whereas there is no increased incidence of isolated cleft palate. Conversely, relatives of a proband with cleft palate show an increased prevalence of this anomaly, but without a concurrent rise in cases of cleft palate combined with cleft lip. Although exceptions may occur, it is generally considered that these seemingly similar developmental defects have distinct genetic etiologies. The role of genetic factors is further supported by a frequently pronounced familial aggregation and a higher concordance rate in monozygotic twins than in dizygotic ones. Thus, the recurrence risk for the second twin when the first is affected is 33% for monozygotic twins, compared to only 5% for dizygotic twins.

Clinical and genetic analysis shows that cleft lip and palate are more prevalent among close relatives than among distant relatives of the proband. For instance, while the population frequency of cleft lip is less than 0.1% and that of cleft palate is 0.04%, in families that already have an affected child and healthy parents, the probability of the next child being born with the condition rises to 4% for cleft lip and 1.8% for cleft palate. If there is already an affected child and one of the parents also presents with this anomaly, the probability for subsequent children increases even further, reaching 14–17%.

Anencephaly and spina bifida can run in families and are particularly common among siblings in households where one child is already affected. The dependence of the incidence rate on parental consanguinity confirms the role of genetic factors. Currently, it is difficult to propose a hypothesis for the development of these anomalies based solely on a single factor, whether hereditary or exogenous. Anencephaly is likely best regarded as a polyetiological syndrome.

Congenital hip dislocation. Clinical and genetic analysis demonstrates a higher concordance rate in monozygotic twins than in dizygotic twins. Specifically, the probability of the second twin being affected if the first has the condition is 41.4% for monozygotic twins and 2.8% for dizygotic twins. Evidence also points to a higher prevalence of this anomaly among siblings and descendants of affected individuals. While the population frequency of congenital hip dislocation is 0.1%, in families with one affected child and healthy parents, the recurrence risk for a second child rises to 5%, and if one of the parents also has this anomaly, it increases to 10–15%.

Clubfoot and talipes equinus are significantly more common among the relatives of a proband than in the general population. While the population frequency of this deformity is 0.1%, in families with an affected child and healthy parents, the risk for a subsequent child increases to 5–10%. Twin studies reveal a higher concordance rate in monozygotic twins compared to dizygotic twins. For instance, the recurrence risk for the second twin when the first is affected is 32% for monozygotic twins and 3% for dizygotic twins.

The study of genetically determined congenital malformations is important not only for timely Diagnosis and Treatment, but also for Genetic Counseling. Medical Genetic Counseling for Congenital Malformations focuses on the most critical aspects of Prevention: providing parents with objective information regarding the potential recurrence risk for their children; explaining the consequences of marriages between heterozygotes carrying the same mutant gene (especially in cases of consanguinity); and offering appropriate guidance to families with a history of congenital anomalies (such as advising against childbearing in older mothers, etc.). In such cases, Clinical and Genealogical data regarding the specific family must be carefully evaluated, as there may be unique features in the mode of inheritance, penetrance, or the clinical manifestation of the congenital syndrome itself.

The goals of preventing congenital malformations call for the further development of specialized medical genetics departments and their staffing with highly qualified clinical geneticists.