Genetic and Congenital Anomalies

Introduction

Structural or functional abnormalities which may occur during intrauterine life are known as congenital anomalies. They are also called congenital malformations or birth defects. Identification of these can be made prenatal, at birth, or later in life. They have a variety of causes such as pregnancy, birth complications, genetic malformations, or viral infections. Sometimes the cause of these anomalies is not known.

Various genetic and environmental issues may result in these congenital anomalies. Various errors of infection, epigenetic modifications, morphogenesis, or chromosomal abnormality lead to such defects. According to previous studies, mother’s and father’s diet, glucose levels before ovulation and conception, Vitamin intake lead to long-term effects on the growth of the fetus. Father’s food habits, germline mutations, alcohol use, chemical mutagens, age, smoking habits, and epigenetic alterations can lead to such anomalies.

Congenital anomalies are broadly divided into three categories:

  • 1.Isolated conditions
  • 2.Generalized conditions
  • 3.Spinal deformities.

1.Isolated Conditions

These conditions are divided based on their anatomical location. These conditions may or may not occur together with other different types of congenital anomalies.

  • Shoulder Girdle

It is usually related to congenital anomalies of the cervical and upper thoracic spine. It is also known as Klippel-Fiel syndrome. It can be unilateral or bilateral. When it is due to birth trauma of brachial nerve plexus, then it is found unilateral only but if it is due to hypoplasia of glenoid due to growth disturbances then it is found bilaterally.

  • Madelung Deformity (Wrist Maldevelopment)

V-shaped deformity of the wrist is known as Madelung deformity which is caused due to growth disturbance of the medial aspect of the distal epiphysis. This is mostly found in females and is commonly revealed in the teenage years. The main reason for its occurrence is localized trauma or infection which causes premature fusion of part of the growth plate. These wrist maldevelopments may go together with other bone dysplasias like hemochromatosis and diaphyseal aclasis.

  • Duplication, hypoplasia, and agenesis of upper limb bones

Various congenital upper limb anomalies can be encountered from minor to severe ones. One of them is the duplication of bones. Others may include hypoplasia and agenesis which affects the upper limb bones diagonally or longitudinally. Some syndromes which are associated with congenital heart disease may show radial hypoplasia. Synostosis i.e. congenital fusion of bones is mostly found in the wrist.

  • Congenital dysplasia of the hip

One of the most common sites of congenital dislocations is the hip joint. This type of congenital dislocation is common in Caucasians as compared to China and parts of Africa. The ball and socket joint is present in the hip. If the ‚Äúball‚ÄĚ of the femoral head is not retained within the ‚Äúsocket‚ÄĚ during growth, the acetabulum will fail to develop and will appear abrupt and narrow. A false acetabulum with lateral ilium is developed if congenital dislocation of the hip is imperfectly treated. Since the femoral head will migrate upwards this false development will take place.

  • Legg-Calv√©-Perthes disease (coxa plana)

It is also known as Perthes disease. Proximal femoral epiphysis undergoes osteonecrosis in children between the ages 4 and 8 years which leads to this disease. The occurrence of this disease varies with geographical area and is commonly seen in boys.

In about 10% of cases, it is bilateral but it does not start at both sides at the same time. Symmetric radiographic appearances cannot be observed and it becomes an important feature in differentiating between Legg-Calvé-Perthes disease and other conditions like cretinism or epiphyseal dysplasias with a fragmented proximal femoral epiphysis.

In advanced stages of this disease increased sclerosis, flattening and fragmentation of proximal femoral epiphysis can be seen. Secondary growth disturbances of the acetabulum and irregularity of the proximal femoral metaphysis are observed in severe cases.

  • Slipped upper femoral epiphysis

It is also known as slipped capital femoral epiphysis. It mostly occurs in adolescence. The femoral head gradually slips posteriorly, medially, and inferiorly concerning the neck. Due to shear stresses, this slip occurs when the growth plate is weak. Most commonly seen in boys as compared to girls and in about 30% of cases, it is bilateral. Some of the observations include blurring of the growth plate, decreased height of femoral epiphysis, and medial migration. The slip is readily apparent on the ‚Äúfrog-lateral‚ÄĚ projection.

  • Proximal focal femoral deficiency

It is a rare congenital anomaly. It is characterized by fluctuating degrees of hypoplasia of the proximal third of the femur.

  • Congenital tibia vara (Blount‚Äôs disease)

It is a condition that affects the development of a medial portion of the proximal tibial growth plate. It is of 2 types i.e. unilateral and bilateral. In case of improper growth of medial tibial epiphysis and metaphysis, progressive deformity of the knee develops. In case of premature fusion of the medial aspect of the proximal tibial growth plate occurring due to inflammation (infectious or non-infectious) or trauma; a similar type of deformity can be observed.

  • ‚ÄúBall-and-socket‚ÄĚ ankle

In this disease, the ankle joint develops into a ball and socket appearance. The curved articular surface of the lower tibia and upper talus can be seen.

  • Talipes Equino varus

It is also called clubfoot. Hindfoot equinus, forefoot varus, hindfoot varus, and high arch are some of the deformities which can be seen in neuromuscular disorders.

  • Vertical talus

It is a congenital anomaly with extreme plantar flexion of the talus and dorsal dislocation of the navicular. It leads to rigid flat feet.

  • Tarsal coalition

A single structure is formed by the fusion of two or more tarsal bones in this anomaly. The fusion may be complete or incomplete and the bridge formed may be osseous, cartilaginous, or fibrous. Even though it is a congenital disease, its symptoms appear in adolescence or early adulthood. Fusion of the middle subtalar joint between the calcaneus and talus is most commonly seen. The occurrence of multiple variations can be seen.

  • Duplication, hypoplasia, and agenesis of foot bones

Various types of congenital abnormalities of bones of the foot can be seen similar to upper limb disease. It includes duplication, agenesis, and hypoplasia. Since the functioning of the foot is less sophisticated as compared to the upper limb, the problems caused are comparatively fewer.

2.Generalized Conditions

Various rare birth defects are present which can affect the skeleton to a huge or less extent. Most of them are very rare and require little mention. Radiographs are required for the establishment of correct diagnosis. They are generally classified as skeletal dysplasias.

Most conditions fall into the following broad categories such as dysplasia with predominantly epiphyseal involvement (with or without spinal involvement), dysplasia with predominantly metaphyseal involvement (with or without spinal involvement), dwarfisms, storage diseases, inherited metabolic disorders, dysplasia with reduced bone density, dysplasia with increased bone density, tumor-like dysplasia, and malformation syndromes.

Some of the common conditions are:

  • Multiple epiphyseal dysplasias

Premature degenerative changes are caused due to symmetrical irregular growth of epiphysis.

  • Achondroplasia

It is the most common type of dwarfism with short limbs. The proximal segments of the limb are shorter than the distal segments. E.g. femur is shorter than the tibia and fibula. Flared metaphyses and normal epiphysis can be observed with shortened long bones. With horizontal acetabular roofs, the iliac bones appear square.

The interpedicular distance increase from upper to lower limb in the normal individual but in this condition, it decreases. Adult achondroplastic dwarfs have more chances of developing multiple levels of spinal canal stenosis which causes nerve root irritation, paraplegia, and paraparesis.

  • Osteogenesis imperfecta

Bone density is severely reduced in this condition. It is a connective tissue disorder. Due to reduction in bone density, over the tabulation of long bones and multiple fractures can occur which have slow healing and leave marked residual deformity. There are various forms of this disease. Babies suffering from the severe condition are usually stillborn or die early. Infants who survive have a less severe form.

  • Sclerosing bone dysplasias

Focal or generalized sclerosis of bone can occur because of several bone dysplasia. Multiple small bone islands clustered at the bone ends around the joints known as osteopoikilosis, variable amounts of cortical and endosteal new bone formation likened to the pattern of dripping candle wax known as melorheostosis, generalized bone sclerosis resulting in brittle bones with an increased tendency to fracture known as osteopetrosis, the distribution of bony sclerosis can exhibit a mixed pattern combining features from two or more known as mixed sclerosing bone dysplasia are included in it.

  • Tumor-like dysplasias

Multiple osteochondromas, multiple enchondromas, and polyostotic fibrous dysplasia are included in this category. Individuals with diaphyseal aclasis and Ollier’s disease have a small probability of one of their lesions malignantly transforming into low-grade cancer.

3.Spinal Deformity

  • Scoliosis

Scoliosis may be idiopathic, congenital, neuromuscular, and others which include trauma, infection, and tumors.

  • Idiopathic scoliosis

About 70% of cases of scoliosis are idiopathic scoliosis. It is of three types depending on age presentation i.e. infantile, juvenile, and adolescent. 85% of cases are seen in adolescents in which the number of girls affected is comparatively more than boys. It usually involves the thoracolumbar spine with the convexity of the principal curve to the right.

  • Congenital scoliosis

About 10% of cases of scoliosis are of congenital origin. It is caused due to underlying congenital vertebral abnormalities. Hemivertebra i.e. failure of formation of the vertebra, spina bifida i.e. the failure of segmentation of vertebra are included in it. There is a recognized link between congenital scoliosis and other anomalies such as spinal tethering and diastematomyelia (bony or fibrous bar across the spinal canal).

Clefting

During the gestation period, facial and oral malformations can occur which result in cleft lip and cleft palate or both. The formation of lips occurs between four to seven weeks of pregnancy. If insufficient tissues are present in the mouth or lip area and the tissue available does not join properly, it results in clefting.

Cleft lip

A cleft lip is a physical split or separation of two sides of the upper lip that shows as a small gap in the upper lip’s skin. It frequently extends beyond the nose’s base. Bones of the upper jaw or gum are included in it.

It can be categorized as incomplete or partial cleft lip in which the top of the lip has a small gap and complete cleft lip in which the gap continues till the nose. It can be unilateral, which means it just affects one side of the upper lip or bilateral means it affects both sides.

Cleft palate

When there is a split or opening in the roof of the mouth i.e. the palate then it is known as cleft palate. It may involve a hard palate or soft palate. A cleft palate can occur as complete in which gap is present in the soft and hard palate. It is possible to include a gap in the jaw or incomplete in which there is a ‚Äėhole‚Äô in the roof of the mouth. It is usually a cleft soft palate. It can also be unilateral or bilateral.

Cleft lip and Cleft palate

They can occur on both sides of the mouth. Since the lips and palate develop separately, it is possible to have only cleft lip or cleft palate, or both. In the case of cleft lip and cleft palate, both the lip and palate have a split. It can occur on one or both sides of the mouth.

Chromosomal Variations

The phenotypic is affected by the addition (47, XXY) or deletion (45, X) of an X chromosome from a diploid genome. It results in Klinefelter Syndrome or Turner Syndrome, respectively. Human females may contain extra X chromosomes (e.g., 47, XXX, 48, XXXX). An additional Y chromosome can be found in some males (47, XYY). These variations in chromosomes arise due to the random errors during the process of gamete formation, also known as non-disjunction wherein paired homologous chromosomes fail to disjoin during segregation.

Fragile-X Syndrome (Martin-Bell Syndrome)

Sometimes, gaps appear at positions within the set of chromosomes, and such areas eventually came to be known as fragile sites. While most fragile sites do not appear to be associated with any clinical syndrome, individuals bearing a folate-sensitive site on the X chromosome exhibit the fragile-X syndrome (or Martin-Bell syndrome). Inherited mental retardation is the most common form. About 1 in 4000 males and 1 in 8000 females are affected by this syndrome. The disorder is categorized as a dominant trait because affected females usually only have one fragile X chromosome. Fortunately, penetrance is not complete, and only around 30% of fragile X-bearing females and 80% of fragile X-bearing males fully show the trait. Affected males have long, narrow faces with protruding chins, larger ears, increased testicular size, and mental retardation.

error: Content is protected !!