SNP Shot: Genomic Insights

Autosomal recessive congenital methemoglobinemia is a genetic disorder primarily impacting red blood cells and their function. This condition disrupts hemoglobin, a molecule in red blood cells responsible for transporting oxygen throughout the body. In affected individuals, a portion of the normal hemoglobin is replaced by methemoglobin, an abnormal form that cannot effectively deliver oxygen to the body's tissues. This oxygen deprivation results in cyanosis, a bluish discoloration of the skin, lips, and nails.

There are two subtypes: type I and type II. Individuals with type I exhibit cyanosis from birth and may experience weakness or shortness of breath due to insufficient oxygen reaching their tissues. Type II also presents with cyanosis, but additionally involves significant neurological issues. Children with type II may initially develop normally for a few months before developing encephalopathy (severe brain dysfunction), dystonia (uncontrolled muscle tension), and choreoathetosis (involuntary limb movements). They also experience microcephaly, where their head size remains smaller than expected for their age. Individuals with type II have severe intellectual disability, can recognize faces and typically babble, but do not develop speech. They can sit independently and grasp objects, but their impaired motor skills prevent them from walking. Growth is often stunted in type II. Difficulty swallowing, due to abnormal facial muscle movements, can lead to feeding problems and further growth delays.

While individuals with type I of autosomal recessive congenital methemoglobinemia typically have a normal life expectancy, those with type II often do not survive beyond early adulthood.

Inheritance:

This disorder follows an autosomal recessive inheritance pattern. This means that both copies of the relevant gene in each cell must carry a mutation for the condition to manifest. Both parents of a person with an autosomal recessive disorder carry one copy of the mutated gene but usually do not exhibit any signs or symptoms of the condition themselves.