**Question:** ATM mutation is seen in

A. Down syndrome
B. Fanconi anaemia
C. Bloom syndrome
D. Spinal muscular atrophy

**Core Concept:** Autosomal recessive disorders are genetic conditions caused by mutations in genes that are located on non-sex chromosomes (autosomes). These mutations can lead to various clinical manifestations and organ systems involvement.

**Why the Correct Answer is Right:** The correct answer is B. Fanconi anaemia (FA) because FA is a genetic disorder caused by mutations in the FANCA gene on chromosome 8p. This gene is part of a larger group of genes (FANC genes) that work together to maintain genomic stability and protect cells from DNA damage.

**Why Each Wrong Option is Incorrect:**

A. Down syndrome (DS) is caused by an extra copy of chromosome 21, not a mutation in the ATM gene. ATM is involved in the detection and repair of DNA double-strand breaks, and mutations in this gene may lead to different clinical conditions, such as Ataxia-Telangiectasia (A-T), which is an autoimmune disorder affecting multiple organ systems, including the nervous system, immune system, and gastrointestinal tract.

C. Bloom syndrome is a rare disorder caused by mutations in the BLM gene, which is located on chromosome 15q26. The correct answer is not related to the ATM gene.

D. Spinal muscular atrophy (SMA) is a genetic disorder caused by mutations in the SMN1 gene on chromosome 5q15, not a mutation in the ATM gene. ATM is involved in detecting DNA double-strand breaks, while SMA is a neuromuscular disorder caused by a deficiency in the Survival motor neuron (SMN) protein, which is produced by the SMN1 gene.

**Clinical Pearl:** Understanding the distinction between genetic disorders caused by mutations in specific genes is crucial for accurate diagnosis and management of patients. Different genes and their associated disorders have distinct clinical features and outcomes, which can guide clinicians in selecting appropriate therapies and counseling for affected individuals and families.