Which primary immunodeficiency presents in male infants with recurrent sinopulmonary infections after 6 months, absence of germinal centers in nodes, low IgG, and a family history suggesting X-linked disease?

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Multiple Choice

Which primary immunodeficiency presents in male infants with recurrent sinopulmonary infections after 6 months, absence of germinal centers in nodes, low IgG, and a family history suggesting X-linked disease?

This scenario tests recognizing a defect in B cell development that leads to pan-hypogammaglobulinemia with absent germinal centers in lymphoid tissue. In male infants, infections starting after six months often reflect waning maternal IgG, revealing an underlying humoral deficiency. The hallmark findings are very low IgG (and usually low other immunoglobulins) and a marked reduction or absence of circulating mature B cells, which explains why germinal centers—areas in lymph nodes where B cells normally mature and class-switch—are absent. The X-linked pattern is suggested by the male-only presentation and a family history pointing to this inheritance. Bruton’s agammaglobulinemia arises from a mutation in BTK, which blocks B cell development at an early stage in the bone marrow. Without mature B cells, antibody production across all classes is severely impaired, and germinal centers fail to form because they depend on B cells. This directly accounts for the recurrent sinopulmonary infections with encapsulated bacteria seen after maternal antibodies wane. Other primary immunodeficiencies don’t fit as well. Severe combined immunodeficiency typically involves both T and B cell defects and presents with infections very early in life, not just after six months. Common variable immunodeficiency usually presents later in childhood or adulthood with low immunoglobulins but is not characteristically X-linked and does not feature absent germinal centers from infancy. IgA deficiency often has normal IgG levels and primarily mucosal issues, without the broad humoral deficiency or absence of germinal centers described here. Management focuses on lifelong immunoglobulin replacement and prompt treatment of infections, along with genetic counseling for X-linked inheritance.

This scenario tests recognizing a defect in B cell development that leads to pan-hypogammaglobulinemia with absent germinal centers in lymphoid tissue. In male infants, infections starting after six months often reflect waning maternal IgG, revealing an underlying humoral deficiency. The hallmark findings are very low IgG (and usually low other immunoglobulins) and a marked reduction or absence of circulating mature B cells, which explains why germinal centers—areas in lymph nodes where B cells normally mature and class-switch—are absent. The X-linked pattern is suggested by the male-only presentation and a family history pointing to this inheritance.

Bruton’s agammaglobulinemia arises from a mutation in BTK, which blocks B cell development at an early stage in the bone marrow. Without mature B cells, antibody production across all classes is severely impaired, and germinal centers fail to form because they depend on B cells. This directly accounts for the recurrent sinopulmonary infections with encapsulated bacteria seen after maternal antibodies wane.

Other primary immunodeficiencies don’t fit as well. Severe combined immunodeficiency typically involves both T and B cell defects and presents with infections very early in life, not just after six months. Common variable immunodeficiency usually presents later in childhood or adulthood with low immunoglobulins but is not characteristically X-linked and does not feature absent germinal centers from infancy. IgA deficiency often has normal IgG levels and primarily mucosal issues, without the broad humoral deficiency or absence of germinal centers described here.

Management focuses on lifelong immunoglobulin replacement and prompt treatment of infections, along with genetic counseling for X-linked inheritance.

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