About dmc disease

What is dmc disease?

Dyggve-Melchior-Clausen (DMC) syndrome is a rare, progressive genetic disorder characterized by abnormal skeletal development, microcephaly and intellectual disability. The condition was first reported by Dyggve, Melchior and Clausen in 1962 in three of eight siblings where the father was the mother's paternal uncle. Because of physical appearance and the present of acid mucopolysaccharides in the urine, Dyggve believed that their affected patients had Morquio-Ullrich disease (now Morquio syndrome). Skeletal abnormalities in this condition may include a barrel-shaped chest with a short truck, partial dislocation of the hips, genu valgum (knocked knees) or varum (bowed legs), and decreased joint mobility. In 11% of patients, there is atlantoaxial (upper neck vertebrae) instability that can lead to spinal cord compression, weakness and paralysis. Normally, there is growth deficiency resulting in short stature. Radiographic findings in older children and adults are pathognomonic for the disorder. DMC results from mutations in the DYM (dymeclin) gene and is inherited in an autosomal recessive mode.

A variant of DMC syndrome, Smith-McCort syndrome (SMS), which was first described by Smith and McCort in 1958, has identical skeletal abnormalities, but lacks the intellectual disability. SMS is also caused by mutations in DYM, and thus is allelic to DMC. Both are classified as osteochondrodysplasias, specifically a spondyloepimetaphyseal dysplasia; this latter category of dysplasias consists of 28 separate disorders.

What are the symptoms for dmc disease?

Coarse facial appearance symptom was found in the dmc disease condition

Affected newborns may be small at birth, but otherwise appear normal. With age, other characteristics develop. For instance, chest deformities, feeding difficulties and developmental delay usually are manifest by or before 18 months. Disproportionate short stature, with the arms and legs being disproportionately too long for the torso, typically is present after 18 months. Additional clinical features that may also develop include dolichocephaly (a long skull), Microcephaly (a small head), coarse facial appearance, prognathism (a protruding lower jaw). Intellectual disability ranges from moderate to severe, and worsens with age. Microcephaly occurs in most individuals. Thinning of the corpus callosum has also been reported. The overall health of an affected person is generally good and survival into adulthood is usual.

In addition to the skeletal abnormalities listed above, affected individuals can also develop a short neck and chest, pectus carinatum (protruding breastbone), flaring of the costal margins, kyphosis (excessive backward curvature of the spine), lumbar lordosis (abnormal forward curvature of the spine), scoliosis (side-to-side curvature of the spine), claw-like hands, other joint contractures especially of the elbows and hips, genu valgum and talipes equinovarus (clubbed feet). Further, the metacarpals (bones in the middle of the hand) and phalanges (other bones in the fingers and toes) are shortened. The carpal bones (bones of the wrist) may also be small and irregularly shaped. Rhizomelic shortening of the limbs (disproportionate shortening of the proximal portion of the limbs) may be present also. Histologically, both DMC and SMS exhibit deficient chondrocytic organization and differentiation, and columnar formation that contain populations of degenerating cells with rough endoplasmic reticulum inclusions. On electron microscopic exam, the chondrocytes contain widened cisternae of the rough endoplasmic reticulum, and the vesicles are coated with a smooth single-layered membrane. The above findings suggest that lack of dymeclin may lead to abnormal processing or defective synthesis of cartilage protein.

Other radiographic abnormalities seen in DMC have been extensively reviewed by Spranger et al. (1975) and include a small skull, hypoplastic facial bones, malformed or absent carpal bones, cone-shaped epiphyses of the phalanges, brachydactyly, fifth finger clinodactyly, accessory bones in the hands, odontoid hypoplasia (underdevelopment of the peg-like projection of the second cervical vertebra) with atlantoaxial instability, platyspondyly (flattened vertebral bodies), irregular superior and inferior edges of the vertebral bodies, anterior pointing of the vertebral bodies, hypoplastic ilia (small hipbones), narrow sacrosciatic notch, widen pubic symphysis, dysplastic acetabulum (malformation of the hip socket), small femoral heads (proximal ends of the femurs), and broad metaphyses of the long bones. Bone maturation (bone age) is delayed. Individuals with Smith-McCort syndrome have similar skeletal findings as those associated with DMC.

Secondary problems resulting from the skeletal abnormalities associated with DMC may include spinal compression, dislocated hips and restricted joint mobility. These problems may in turn cause a waddling gait. When it occurs, spinal cord compression in the neck is usually caused by the hypoplasia of the odontoid process and to hyperlaxity of the longitudinal ligament of the upper cervical spine. The pathognomonic radiographic findings for DMC and SMS include constrictions in the middle third of the vertebral bodies (a double-humped appearance), and a lacy appearance of the upper portion of the iliac crest (hipbone). This latter feature because less prominent with time and disappears by adulthood.

MRI findings in DMC include hypoplasia of the odontoid process, posterior disk protrusions in the lumbar vertebrae and the enlargement of the posterior common vertebral ligament. In most individuals with DMC, MRI analyses of the brain have been normal. However, one patient has been reported with cortical atrophy and another with thinning of the corpus callosum.

Both DMC and SMS are progressive disorders. With the exception of reduced length, affected individuals usually are normal at birth. Skeletal findings often are recognized first between 1 and 18 months. The vertebral body constriction abnormalities and lacy pattern of the iliac crests appear by 3-4 years and may persist until adulthood. The vertebral body constrictions are most prominent between ages 8 and 12 years. The Microcephaly in DMC and Short stature in both appear during childhood. Throughout childhood and as adults, thoracic kyphosis, scoliosis, lumbar lordosis, subluxation (partial dislocation) and frank dislocation of the hips, wide-based and waddling gait, genu valgum or varum, and restricted joint mobility appear and may worsen. The treatment of genu varum in this condition has been reported. Adult height is severely reduced with height ranging from 82 cm to 128 cm (32 in to 50 in). Neurologic and behavioral complications in DMC may include hyperactivity, autistic-like behavior, lack of speech and mild to severe Intellectual disability with IQ scores ranging from 25 to 65. Because of the of atlantoaxial instability found in DMC, cord compression is a concern. However, only a few cases have been reported with this complication. Prenatal diagnosis of DMC has been accomplished by finding a pathogenic homozygous mutation in the DYM gene in a fetus with no detectable physical findings.

What are the causes for dmc disease?

Dyggve-Melchior-Clausen syndrome is inherited as an autosomal recessive trait. Normally, autosomal genes come in pair with an individual receiving one gene of the paired genes from his or her father, and the other from the mother. Recessive genetic disorders occur when an individual inherits an abnormal or mutated gene for the same trait from each parent. In autosomal recessive conditions, if an individual receives one normal gene and one gene for the disease, the person is a carrier for the disease, but usually will not have any clinical manifestations of the condition. The risk for two carrier parents to both pass on their defective genes to an offspring, and therefore have an affected child, is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. And the chance for a child to receive two normal genes from his or her parents and be genetically normal for that particular trait is 25%. Many children with DMC and SMS are offspring of consanguineous parents with many reported patients being from Morocco or other Mediterranean countries.

Smith-McCort syndrome is allelic to DMC, and also is inherited as an autosomal recessive trait. There has been some confusion about the inheritance of SMS because Yunis et al. (1980) reported a family with apparent SMS where the condition was inherited in an X-linked mode. . Subsequently, Spranger (1981) suggested that this family had spondyloepiphyseal dysplasia tarda, a well-established X-linked disorder.

The gene that causes both DMC and SMS was first reported by Cohn et al. (2003), which they originally called FLJ90130. Subsequently, others proposed changing the gene’s name, and the protein it produces, to dymeclin (abbreviated from Dyggve-Melchior-Clausen). The gene now most commonly is referred to as DYM. The gene is located on the long arm (q) of chromosome 18 (18q12-q21.1), contains 17 exons and spans about 400 kb. The protein, dymeclin, is a protein of 669 amino acids, and is a protein involved in the Golgi apparatus. Dymeclin’s functions in the homeostasis and organization of the Golgi apparatus, and in trafficking of vesicles and proteins into and out of this organelle. DMC appears to be produced mostly by premature truncation of the DYM product resulting in complete or nearly complete absence of dymeclin production from both DYM genes. Alternatively, there may be little or no production from one gene and production of a partially functioning protein from the other. A number of different types of mutations, i.e., frameshift, nonsense, missense mutations and etc., cause DMC and at least 58 different DYM mutations in multiple families from different ethnic groups have been reported. Some mutations in DYM appear to result in mis-localization and subsequent degradation of dymeclin with in the cell. Interestingly, disease producing mutations in this gene are scattered throughout the gene. Smith-McCort syndrome usually is the result of missense mutations in the same gene. Mutational analysis of DYM currently is available.

More recently a second gene, RAB33B, has been reported to causes SMS. These investigators reported on a Saudi inbred family with six affected individuals in two sibships all of whom had clinical and radiographic features consistent with DMC/SMS. Four tested children each had the same missense mutation in the RAB33B gene. The gene encodes for a Rab protein and the mutation lead to a marked deficiency of this protein. Like dymeclin, the Rab protein plays a critical role in Golgi transport. All four of the evaluated children had normal cognitive function and head size. Thus, it appears that the siblings had SMS rather than DMC has claimed by the authors. Another individual with SMS and a mutation in RAB33B has been reported.

What are the treatments for dmc disease?

Treatment of individuals with DMC syndrome is symptomatic and supportive. When there is hypoplasia of the odontoid process and partial dislocation of the cervical vertebrae (the segments of the spinal column at the top of the spine), spinal fusion of these vertebrae or other means of vertebral stabilization normally is indicated. These procedures should be done in order to prevent damage to the cervical spinal cord, which can result in cord-related weakness or paralysis. Additionally, surgical techniques may be used to correct various other skeletal abnormalities such as subluxation or dislocation of the shoulder and hip joints. In some individuals, hip replacement is required.

Children with DMC syndrome may benefit from early intervention and special educational programs. Genetic counseling may be of benefit for affected individuals, their parents and other family.

What are the risk factors for dmc disease?

DMC (Dyggve-Melchior-Clausen) is a rare genetic syndrome. It results from mutations in the dymeclin gene. It is inherited as an autosomal recessive type of disorder. The affected child receives one gene from the father and another from the mother. If one gene is normal and the other one is of disease then the person becomes the carrier of the disease. There occurs abnormal skeletal development, microcephaly (a small head), intellectual disability, dolichocephaly (a long skull), coarse facial appearance, prognathism (a protruding lower jaw). Skeletal abnormalities include a barrel-shaped chest with a short truck, partial dislocation of the hips, genu valgum i.e. knocked knees, varum i.e. bowed legs, decreased joint mobility. There can also occur spinal cord compression, weakness and paralysis due to atlantoaxial. Even there can be growth deficiency. This disease can affect the newborn and develop overtime. The chest deformities, feeding difficulties, developmental delay occur before 18months whereas disproportionate short stature, with the arms and legs that are disproportionately too long for the torso occur after 18months. Some may have a short neck and chest, pectus carinatum (protruding breastbone), flaring of the costal margins, kyphosis (excessive backward curvature of the spine), lumbar lordosis (abnormal forward curvature of the spine), scoliosis (side-to-side curvature of the spine), claw-like hands. The vertebral body constriction is common in ages 8 and 12 years. Microcephaly and short stature occurs during childhood. The risk of neurological and behavioural complications are hyperactivity, autistic like behaviour, lack of speech, mild to severe intellectual disability that has IQ scores from 25 to 65.

Is there a cure/medications for dmc disease?

DMC Disease (Dyggve-Melchior-Clausen) is a rare genetic syndrome. It results from mutations in the dymeclin gene. It is an inherited disorder. The affected child receives one gene from the father and another from the mother. If one gene is normal and the other one is of disease, then the person becomes the carrier of the disease. There occurs abnormal skeletal development, microcephaly (a small head), intellectual disability, dolichocephaly (a long skull), coarse facial appearance, and prognathism (a protruding lower jaw). Skeletal abnormalities include a barrel-shaped chest with a short truck, partial dislocation of the hips, genu valgum, i.e. knocked knees, varum i.e. bowed legs, and decreased joint mobility. Spinal cord compression, weakness and paralysis can also occur due to atlantoaxial. Even there can be growth deficiency.

This disease can affect the newborn and develop over time. Chest deformities, feeding difficulties, and developmental delay occur before 18 months, whereas disproportionate short stature, with the arms and legs that are disproportionately too long for the torso, occurs after 18 months.

Cure/medications for DMC disease-
1. It depends on the type of symptom the patient is suffering from.
2. Surgical techniques are recommended for skeletal abnormalities such as subluxation or dislocation of the shoulder and hip joints. Also, in some cases, hip replacement is necessary.
3. Special educational programs and early intervention are beneficial for children suffering from DMC disease. Genetic counselling can help all the affected persons, their parents and other families.

Symptoms
Chest deformities,Feeding difficulties and developmental delay usually are manifest by or before 18 monthsdolichocephaly (a long skull),Microcephaly (a small head),Coarse facial appearance,Prognathism (a protruding lower jaw)
Conditions
Abnormal skeletal development,Microcephaly,Intellectual disability
Drugs
Surgery

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