ALG 12-CDG

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Faults within the ALG12 gene are believed to cause ALG12-CDG. This gene provides instructions for making an enzyme that is involved in a process called glycosylation. During this process, complex chains of sugar molecules are added to proteins and fats. Glycosylation modifies proteins and lipids so they can fully perform their functions. The enzyme produced from the ALG12 gene transfers a simple sugar called mannose to growing sugar chains at a particular step in its formation. Once the correct number of sugar molecules are linked together, it is attached to a protein or lipid.

ALG12 gene mutations lead to the production of an abnormal enzyme with reduced activity. Without a properly functioning enzyme, mannose cannot be added to the chain efficiently, and the resulting sugar chains are often incomplete.

ALG12-CDG is a very rare condition; its prevalence is unknown. Only a handful of affected individuals worldwide have been described in the medical literature.

Individuals with ALG12-CDG typically develop signs and symptoms of the condition during infancy. Some of the signs and symptoms of this condition are:

• Failure to thrive
• Delayed development
• Low/weak muscle tone (hypotonia)
• Seizures
• Intellectual disabilities
• Cardiac abnormalities
• Frequent infections

Less common abnormalities seen in people with ALG12-CDG include a weakened heart muscle (cardiomyopathy) and poor bone development, which can lead to skeletal abnormalities.

Although these are the main signs and symptoms of this condition it is worth noting that these may not all be present with your child. These symptoms can differ per individual.

A diagnosis of ALG12- CDG may be suspected based upon the identification of characteristic symptoms, a detailed patient history and a thorough clinical evaluation. A variety of specialised tests may be necessary to confirm a diagnosis of CDG and/or to determine the specific subtype. CDG should be considered and ruled out in any unexplained syndrome.

A blood test will be required to check for any abnormalities within the blood system of your child’s body. Molecular genetic testing is needed to confirm a diagnosis of CDG. This procedure will be explained to you if your child is expressing signs of this condition.

The treatment of ALG12-CDG is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of specialists. Paediatricians, neurologists, surgeons, cardiologists, speech pathologists, ophthalmologists, gastroenterologists, and other healthcare professionals may need to systematically and comprehensively plan an affect child’s treatment.

ALG12-CDG can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.

If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.

If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.

Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inheritedALG12-CDG. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own.

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing helen@metabolicsupportuk.org [Resource Library No: AAP002].